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Friday 18 March 2016

How to Build Any Salad Like a Boss

There’s a key challenge when it comes to salad. One loaded up with too many toppings and drowning in heavy dressing can pack as many calories as a bacon cheeseburger (yup, really). On the flip side, a too-skimpy salad can leave you with lingering hunger and lacking in key nutrients. The goal: Build one that’s just right, so when you’re finished you’ll feel full (but not too full), satisfied and energized.
Load your salad up with veggies, grains and lean proteins.

Load your salad up with veggies, grains and lean proteins. Photo Credit santiago__cervantes/Twenty20


This mix-and-match DIY salad guide can help you build a perfectly balanced salad bowl every time. Simply start with a base of greens and add layers using this no-fail formula. We’ve even included five completed salads to get you started — each one using a different greens base. And if you keep these ingredients on hand you can create dozens of unique combinations yourself. And, yes, it’s OK to choose more than one food in each category to keep it interesting.

Follow this DIY salad guide to build the perfect salad every time.
Follow this DIY salad guide to build the perfect salad every time. Photo Credit Melanie Andersen/LIVESTRONG.COM

Go-to Salad Combos

Enjoy these five different salad recipes:

What’s Trending Salad

  • Greens base: Kale
  • Layer 1: Purple cabbage, red onion, mango
  • Layer 2: Salmon, chickpeas
  • Layer 3: Quinoa
  • Layer 4: Tahini
  • Layer 5: Minced garlic, lemon juice, turmeric
Whisk garlic, lemon juice and turmeric into the tahini. Place finely chopped kale in your bowl, top with sliced or shredded purple cabbage, minced red onion and diced mango. Add the salmon, chickpeas and quinoa and drizzle with the seasoned tahini.
TIPS:
Canned wild salmon is perfectly OK to use, as are canned chickpeas. If you have time, pat dry the chickpeas and oven-roast them on a baking sheet until they’re golden and slightly crispy. This salad is naturally gluten-free. If you’re vegetarian or you don’t eat salmon for any reason, leave it out — you’ll still rack up plenty of protein between the chickpeas and quinoa.

Mediterranean Kitchen Sink Salad

  • Greens base: Spinach
  • Layer 1: Tomato, red onion, red grapes
  • Layer 2: Chicken breast, cannellini beans
  • Layer 3: Bulgur
  • Layer 4: Pesto
  • Layer 5: Ground pepper
In a small bowl, toss the diced, grilled or broiled chicken breast and the cannellini beans in pesto. Place the spinach in a salad bowl, top it with the chicken and beans and add sliced tomato, minced red onion and sliced red grapes. Sprinkle with bulgur, and dust with ground pepper.
TIPS:
If you’re crunched for time, buy an all-natural, rotisserie chicken with the skin removed. If you find yourself with extra time, cook the chicken yourself and oven-roast the tomatoes and red onions to enhance their natural sweetness. Hot veggies over crisp greens with chilled fruit can create a mouthwatering texture and temperature contrast that makes this salad even more decadent.

Easy Breezy Southwest Salad

  • Greens base: Red leaf lettuce
  • Layer 1: Red bell pepper
  • Layer 2: Ground turkey, black beans
  • Layer 3: Corn
  • Layer 4: Salsa, guacamole
  • Layer 5: Minced garlic, lime juice, cilantro 
Look for ground turkey that’s at least 93 percent lean and brown it on the stovetop using a mixture of water, minced garlic and freshly chopped cilantro. Toss the chopped lettuce with salsa, top with the seasoned turkey and black beans, and then add the corn and guacamole. If you’re vegetarian or you don’t eat turkey for any reason, omit it and up the portion of black beans for more plant-based protein.
TIPS:
Frozen corn is A-OK. Just transfer it from the freezer to the fridge to thaw or, if you have time, oven-roast it on a baking sheet alongside the red bell pepper. Look for a jarred salsa with an ingredient list that reads like a recipe you could have made yourself (in other words no additives you don’t recognize or can’t pronounce). Same goes for guacamole if you buy it premade. The time-saving shortcut ingredients in this salad make it a quick but incredibly satisfying meal to rely on when you’re running behind.

Nutritionist’s Nicoise Salad

  • Greens base: Field greens
  • Layer 1: Mushrooms, apple
  • Layer 2: Hard-boiled egg, tuna
  • Layer 3: Fingerling potatoes
  • Layer 4: Olive tapenade
  • Layer 5: Crushed red pepper
In a small bowl, toss the field greens with olive tapenade. Transfer to a salad bowl and top with the sliced mushrooms and chopped apple. Add hot or chilled sliced fingerling potatoes, followed by the tuna and sliced hard-boiled egg. Garnish with a sprinkling of crushed red pepper.
TIPS:
To cook washed fingerling potatoes, slice them lengthwise and place on a baking sheet to roast, or wrap them in foil to grill. Cook until they’re soft enough for a toothpick to easily pierce through. Look for tuna canned in water or brands with no water added and fish that’s been sustainably sourced. To make this vegan-friendly, omit the egg and trade the tuna for cannellini beans. If you don’t like your sweet and savory mixed together, leave off the apple and add more of your favorite crunchy veggies.

Healthied-Up BBQ Chicken Salad

  • Greens base: Romaine
  • Layer 1: Purple cabbage, red onion, pineapple
  • Layer 2: Chicken breast, black-eyed peas
  • Layer 3: Yam
  • Layer 4: Barbecue sauce
  • Layer 5: Dried Italian herb seasoning 
Place chopped romaine in a salad bowl. Top with sliced or shredded cabbage, minced red onion and either fresh or canned pineapple chunks. Top with the sliced yam, then the cubed chicken breast and black-eyed peas. Drizzle with barbecue sauce and dust the salad with dried Italian herb seasoning.
TIPS:
All-natural rotisserie chicken with the skin removed is a great option for this salad, as is chicken breast that’s been grilled or broiled. If you opt for canned pineapple, look for one that contains only pineapple and 100 percent pineapple juice with no added sugar. If you choose fresh pineapple, oven-roast or grill slices or cubes to up this salad’s “fanciness factor.” Like salsa, check the ingredients list on barbecue sauces to scope out brands made with all-natural ingredients; and because sauces tend to be sweetened with molasses or brown sugar, try not to be too heavy-handed when you pour.
www.livestrong.com

Nutritional Value of Black Seed

The flowering plant Nigella sativa, native to the Middle East, produces seeds commonly called black seeds or black cumin. People use the seeds in cooking to add spice, and also consume powdered black seed and black seed oil for health benefits, according to Diet Spotlight, a diet and health website. Powdered black seed supplements are available in capsules, as well as oil extract in bottles and softgel capsules. Black seed oil is a good source of essential fatty acids and certain other nutrients.

Nutritional Value of Black Seed

Black seeds in a wooden spoon. Photo Credit joanna wnuk/iStock/Getty Images

Nutrients

Black seed components include amino acids, proteins, carbohydrates, fixed oils, volatile oils, alkaloids, saponin and fiber. Carbohydrates in black seed include the monosaccharides arabinose, glucose, rhamnose and xylose. The seed also contains calcium, iron, potassium, and sodium. Because people generally consume very small amounts of black seed or use the extracted oil as a supplement, there is little nutritional value for the seed itself.

Fixed Oils

Black seed contains fixed oils consisting of 84 percent fatty acids, notes the Memorial Sloan-Kettering Cancer Center. A black seed oil supplement provides 45 calories per teaspoon, all of them from fat. This includes 22 percent alpha-linolenic acid, an anti-inflammatory omega-3 fatty acid, and 59 percent linoleic acid, an omega-6 fatty acid. Dr. Gabe Mirkin explains that although people tend to consider fish oil as the best source of omega-3 fatty acids, seeds and other plant sources also are beneficial.

Potential

Black seed also contains thymoquinone, which has has antioxidant properties and may have protective effects for the liver, Sloan-Kettering reports. Nigellone in black seed inhibits histamine release and may reduce allergy symptoms.



Research

Research with humans is lacking to confirm health benefits from black seed aside from its beneficial fatty acid content, according to Sloan-Kettering. Laboratory and animal studies indicate that individual components of the seed may have antiparasitic and anti-inflammatory effects and may be beneficial for the immune system. Thymoquinone and other components show anticancer effects in animal studies, reducing the growth and size of tumors.

Dosage

A standard dosage of black seed oil is 1 to 2 teaspoons or 2 capsules per day with food. Two capsules typically provide 1,000 milligrams of black seed oil. Negative effects are rare, but very high doses have caused liver and kidney problems in rats during research, cautions Sloan-Kettering.
www.livestrong.com

Is There Any Correlation Between Taking Iron Pills & Vitamin D Deficiency?

As a trace mineral, iron is a nutrient you need in small amounts. This essential substance is a component of enzymes and proteins. Iron also controls cell development and makes it possible for red blood cells to transport oxygen to every area of your body. Vitamin D facilitates calcium absorption to form strong bones and it supports your immune system. No scientific evidence indicates that iron supplementation causes a vitamin D deficiency, though iron levels may be affected by vitamin D.
Is There Any Correlation Between Taking Iron Pills & Vitamin D Deficiency?
Plate of raw oysters Photo Credit pnphotos/iStock/Getty Images

Iron and Vitamin D Interaction

Although iron pills do not deplete your supply of vitamin D, the opposite may occur. According to National Trichology Services, excessive vitamin D or its lengthy supplementation can impair iron absorption. If you must take both the mineral and the vitamin for an extended period, discuss with your doctor what the best course of action is. She may need to order blood tests regularly to monitor you for signs of anemia.

Natural Sources

You may be able to avoid interactions between iron and vitamin D if you can get the recommended daily intake for these nutrients from natural sources. Iron is present in red meats, oysters, legumes and greens. Vitamin D is available from fatty fish, such as salmon and sardines, and egg yolks. Commercial dairies in the United States also fortify their milk with vitamin D. But the simplest way to get the nutrient is by exposing your skin to the sun for 10 to 15 minutes two to three times weekly, which triggers the body to synthesize vitamin D. If your doctor recommends iron or vitamin D supplementation, do not replace the dosages with a natural source without discussing the matter with her first. If you are deficient because of a medical condition that keeps your body from extracting the nutrients from what you eat, taking supplements may be your best option for staying healthy.

Recommended Iron Intake

The Food and Nutrition Board of the Institute of Medicine recommends daily iron intakes based on age and gender. At 19 years of age, a man’s requirement is 8 mg while a woman needs 18 milligrams of iron. Her recommended intake drops to 8 milligrams when she turns 51. Do not exceed these daily values without your doctor’s recommendation and supervision as too much iron can be fatal. Ask a physician before giving iron supplements to a child or adolescent to ensure they receive a safe dose.

Recommended Vitamin D Intake

The Food and Nutrition Board of the Institute of Medicine recommends that all adults, up to 70 years of age, consume 600 international units daily. At 71 years of age or older, adults need to take in 800 IU of vitamin D daily. Do not exceed these values unless your doctor recommends higher intakes. Excessive vitamin D can cause bone loss and kidney stones. Since the nutrient facilitates calcium absorption, too much vitamin D also increases the levels of calcium in your body. The mineral surplus can crystallize and harden your heart.
www.livestrong.com

Vitamins that Enhance the Absorption of Iron

Overview

Iron is an essential mineral for human health, responsible for transporting oxygen from the lungs to the rest of the body. This mineral is part of many enzymes and is used in several cell functions. When you lose too much blood or become pregnant, you may need to increase your iron to keep from having iron-deficiency anemia, which may cause fatigue, weakness, compromised immune function and decreased work or school performance. To replenish your low level of iron, take iron supplements with certain vitamins included to enhance absorption.
Vitamins that Enhance the Absorption of Iron
Large bowl of kale with oranges. Photo Credit Comstock Images/Stockbyte/Getty Images

Vitamin A

Vitamin A is an antioxidant, also known as retinol. The daily recommendation for men is 900 micrograms, or micrograms, a day and for women, 700 micrograms. The Office of Dietary Supplements states that vitamin A is responsible for moving iron from its storage areas within the body. A low level of vitamin A will therefore cause a limitation in iron mobilization.

Vitamin C

Vitamin C is an antioxidant required for a healthy immune system. In addition, vitamin C also works to create connective tissue, collagen and neurotransmitters. Vitamin C also enhances iron absorption. Parenting Science recommends eating an extra 63 milligrams of vitamin C per meal to increase the enhancement of the iron. It's important for absorbing heme iron -- the form of iron found in plant foods, which is otherwise not as easily absorbed as the iron from animal-derived foods.

Eating for Iron Absorption

A well-balanced diet helps ensure you'll get the vitamins you need to absorb and utilize iron. A single serving of grapefruit, strawberries, red pepper, kale or orange will provide the 63 milligrams of vitamin C needed for iron absorption. Kale, oranges, red peppers also provide vitamin A, and a range of other orange and dark green produce -- including mangoes, sweet potatoes, carrots, pumpkin, spinach and chard -- can help you get the vitamin A needed for iron metabolism.
www.livestrong.com

Does Your Iron Have Anything to Do With Your Blood Platelets?

Iron is an essential mineral contained in your red blood cells and is what allows them to carry oxygen to every cell in your body, the University of Maryland Medical Center notes. Iron is also stored in your liver, muscles and bone marrow. Iron deficiency is a typical cause of anemia. Iron deficiency anemia causes your platelet count to increase, according to a study published in a 2009 issue of “Platelets." This suggests that iron levels play a role in platelet production.
Does Your Iron Have Anything to Do With Your Blood Platelets?

A lab technician dropping blood from a dropper into a test tube. Photo Credit Photodisc/Photodisc/Getty Images

Iron Dose

Your body’s daily iron needs vary according to age and gender, the University of Maryland Medical Center says. Infants between the ages of 7 to 12 months need 11 mg/day. Children between the ages of 1 and 3 need 7 mg/day. This increases to 10 mg/day between the ages of 4 and 8. Iron needs drop to 8 mg/day between the ages of 9 and 13. Males between the ages of 14 and 18 need 11 mg/day, while females in the same age group need 15 mg/day. Males over the age of 19 need only 8 mg/day, while females between the ages of 19 to 50 need about 18 mg/day. Females over the age of 50 need about 8 mg/day.

Iron Deficiency Anemia and Thrombocytosis

Thrombocytosis is a disorder that causes your body to produce too many platelets, MayoClinic.com explains. One of the possible causes of thrombocytosis is iron deficiency anemia. The problem with thrombocytosis is your elevated risk of developing potentially fatal blood clots throughout your body. A study published in a 2009 issue of “Platelets” examined the link between iron deficiency anemia and elevated platelet counts. The study took place from November 2006 to April 2008 and involved more than 600 participants with iron deficiency anemia. Only about 13 percent of the participants had thrombocytosis. This suggests that even though iron deficiency anemia causes thrombocytosis the actual degree of elevated platelet count is not necessarily severe.

Platelet Aggregation

The “European Journal of Clinical Investigation” published a study in a 2009 issue that examined the relationship between iron and platelet aggregation. The study involved 111 participants that underwent acute ST segment elevation myocardial infarction, and iron-induced platelet aggregation was measured after clopidogrel, acetylsalicylic acid and tirofiban treatment. An hour after receiving treatment, blood samples were taken from the participants and were added to 100 mg of low carbon steel and incubated for about 15 minutes. The study discovered that iron-induced platelet aggregation was a viable means of gauging platelet aggregation inhibition treatment in patients undergoing stenting for a ST segment elevation myocardial infarction.

Iron and Platelet Function

A 1999 issue of the “European Journal of Clinical Nutrition” published a study that examined the effect of iron and vitamin C antioxidant supplementation on platelet function and low-density lipoprotein oxidation in healthy volunteers. The study used two groups of 20 people who received both iron and vitamin C supplements. The results demonstrated that iron supplements have a positive effect on overall platelet function.
www.livestrong.com

How to Make the Perfect Frittata

Get your morning started right with a frittata.
Get your morning started right with a frittata. Photo Credit Sherrie Castellano/ LIVESTRONG.COM
Frittatas are real crowd pleasers. They’re light and airy, yet hearty and satisfying. They take minimal effort to make, and they can be prepared ahead of time for easy brunch gatherings or breakfast for dinner.
When done right, a frittata is the ultimate meal. They’re an excellent source of healthy protein because of the star of the show — the egg. Each dozen-egg frittata weighs in at no less than nine grams of protein per serving. And eggs, arguably the perfect food, are loaded with minerals and vitamins, including A, B-12, D, E, K, selenium and phosphorus.
Who want's eggs? What beauties!
Who want's eggs? What beauties! Photo Credit Sherrie Castellano/ LIVESTRONG.COM
This eggy dish is the perfect vessel to pack in nutrient-dense ingredients, including spinach, mushrooms, onion, peppers, fresh herbs and more. Keep it simple with seasonal vegetable add-ins, or include a lean-meat option for a little extra protein and oomph. We've included three additional combo options to keep the frittata love going all year long.
This frittata party is about to go down.
This frittata party is about to go down. Photo Credit Sherrie Castellano/ LIVESTRONG.COM

Spring Frittata With Artichokes, Peas, Green Onions and Goat Cheese

  • Serves: 8
  • Prep time: 5 minutes
  • Cook time: 25 minutes

Ingredients

  • 12 fresh eggs
  • 1/4 cup of whole milk
  • 2 tablespoons of butter, ghee or olive oil
  • 1 cup of peas
  • 1 cup of cooked artichoke hearts
  • 1 cup of green onions, chopped
  • 3 to 4 ounces of goat cheese, crumbled
  • sea salt and black pepper to taste

Directions

  1. Preheat the oven to 350 degrees. 
  2. Heat butter over medium heat in a 10-inch cast-iron skillet.
You got your milk. You got your eggs.
You got your milk. You got your eggs. Photo Credit Sherrie Castellano/ LIVESTRONG.COM
3. In a separate bowl, combine the eggs with the milk.
Now mix it all together.
Now mix it all together. Photo Credit Sherrie Castellano/ LIVESTRONG.COM
4. Whisk the eggs with the milk.
5. Add peas to the cast-iron skillet and stir. Then pour in the egg mixture and top with artichokes, green onions and goat cheese. Cook undisturbed for about 10 minutes or until the edges start to pull away from the skillet.
We're almost there. Yum!
We're almost there. Yum! Photo Credit Sherrie Castellano/ LIVESTRONG.COM
6. Pop the skillet into the oven and cook for 10 to 15 minutes or until the top is completely set. Allow to cool for five minutes, cut and serve warm.

Seasonal Frittata Ideas

Italian Frittata

  • tomatoes
  • shallots
  • mozzarella
  • fresh
    basil 

Savory Fall Frittata

  • diced
    butternut squash sauteed in butter
  • ricotta
  • fresh
    sage

Hearty Irish Frittata

  • mushrooms
  • thinly
    sliced potato
  • cheddar
  • thyme
www.livestrong.com

SUNLIGHT

Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible and ultraviolet light. On Earth, sunlight is filtered through Earth's atmosphere and is obvious as daylight when the Sun is above the horizon. When the direct solar radiation is not blocked by clouds, it is experienced as sunshine, a combination of bright light and radiant heat. When it is blocked by the clouds or reflects off other objects, it is experienced as diffused light. The World Meteorological Organization uses the term "sunshine duration" to mean the cumulative time during which an area receives direct irradiance from the Sun of at least 120 watts per square meter.
Sunlight shining through clouds, giving rise to crepuscular rays.
The ultraviolet radiation in sunlight has both positive and negative health effects, as it is both a principal source of vitamin Dand a mutagen.
Summary
Researchers may record sunlight using a sunshine recorder, pyranometer or pyrheliometer.
Sunlight takes about 8.3 minutes to reach Earth from the surface of the Sun. A photon starting at the centre of the Sun and changing direction every time it encounters a charged particle would take between 10,000 and 170,000 years to get to the surface.
The total amount of energy received at ground level from the Sun at the zenith depends on the distance to the Sun and thus on the time of year. It is about 3.3% higher than average in January and 3.3% lower in July (see below). If the extraterrestrial solar radiation is 1367 watts per square meter (the value when the Earth–Sun distance is 1 astronomical unit, then the direct sunlight at Earth's surface when the Sun is at the zenith is about 1050 W/m2, but the total amount (direct and indirect from the atmosphere) hitting the ground is around 1120 W/m2. In terms of energy, sunlight at Earth's surface is around 52 to 55 percent infrared (above 700 nm), 42 to 43 percent visible (400 to 700 nm), and 3 to 5 percent ultraviolet (below 400 nm). At the top of the atmosphere, sunlight is about 30% more intense, having about 8% ultraviolet (UV), with most of the extra UV consisting of biologically damaging short-wave ultraviolet.
Direct sunlight has a luminous efficacy of about 93 lumens per watt of radiant flux. This is higher than the efficacy (of source) of most artificial lighting (including fluorescent), which means using sunlight for illumination heats up a room less than using most forms of artificial lighting.
Multiplying the figure of 1050 watts per square metre by 93 lumens per watt indicates that bright sunlight provides an illuminance of approximately 98 000 lux (lumens per square meter) on a perpendicular surface at sea level. The illumination of a horizontal surface will be considerably less than this if the Sun is not very high in the sky. Averaged over a day, the highest amount of sunlight on a horizontal surface occurs in January at the South Pole (see insolation).
Dividing the irradiance of 1050 W/m2 by the size of the sun's disk in steradians gives an average radiance of 15.4 MW per square metre per steradian. (However, the radiance at the centre of the sun's disk is somewhat higher than the average over the whole disk due to limb darkening. Multiplying this by Ï€ gives an upper limit to the irradiance which can be focused on a surface using mirrors: 48.5 MW/m2.
Sunlight is a key factor in photosynthesis, the process used by plants and other autotrophic organisms to convert light energy, normally from the Sun, into chemical energy that can be used to fuel the organisms' activities.
Composition and Power

The spectrum of the Sun's solar radiation is close to that of a black body with a temperature of about 5,800 K. The Sun emits EM radiation across most of the electromagnetic spectrum. Although the Sun produces Gamma rays as a result of the nuclear fusion, process, these super-high-energy photons are converted by internal absorption and thermalization to lower-energy photons before they reach the Sun's surface and are emitted out into space. As a result, the Sun does not emit gamma rays from this process, but it does emit gamma rays from solar flares. The Sun also emits X-rays, ultraviolet, visible light, infrared and even radio waves; the only direct signature of the nuclear process is the emission of neutrinos.


Solar irradiance spectrum above atmosphere and at surface. Extreme UV and X-rays are produced (at left of wavelength range shown) but comprise very small amounts of the Sun's total output power.
Although the solar corona is a source of extreme ultraviolet and X-ray radiation, these rays make up only a very small amount of the power output of the Sun (see spectrum at right). The spectrum of nearly all solar electromagnetic radiation striking the Earth's atmosphere spans a range of 100 nm to about 1 mm (1,000,000 nm). This band of significant radiation power can be divided into five regions in increasing order of wavelengths;
  • Ultraviolet C or (UVC) range, which spans a range of 100 to 280 nm. The term ultravioletrefers to the fact that the radiation is at higher frequency than violet light (and, hence, also invisible to the human eye. Due to absorption by the atmosphere very little reaches Earth's surface. This spectrum of radiation has germicidal properties and is used in germicidal lamps.
  • Ultraviolet B or (UVB) range spans 280 to 315 nm. It is also greatly absorbed by the atmosphere, and along with UVC is responsible for the photochemical reaction leading to the production of the ozone layer. It directly damages DNA and causes sunburn but is also required for vitamin D synthesis in the skin and fur of mammals.
  • Ultraviolet A or (UVA) spans 315 to 400 nm. This band was once held to be less damaging to DNA and hence is used in cosmetic artificial sun tanning (tanning booths and tanning beds)  and PUVA therapy for psoriasis. However, UVA is now known to cause significant damage to DNA via indirect routes (formation of free radicals and reactive oxygen species) and is able to cause cancer.
  • Visible range or light spans 380 to 780 nm. As the name suggests, it is this range that is visible to the naked eye. It is also the strongest output range of the Sun's total irradiance spectrum.
  • Infrared range that spans 700 nm to 1,000,000 nm (1 mm). It is responsible for an important part of the electromagnetic radiation that reaches Earth. It is also divided into three types on the basis of wavelength:
    • Infrared-A: 700 nm to 1,400 nm
    • Infrared-B: 1,400 nm to 3,000 nm
    • Infrared-C: 3,000 nm to 1 mm.

Published Tables

Tables of direct solar radiation on various slopes from 0 to 60 degrees North Latitude, in calories per square centimetre, issued in 1972 and published by Pacific Northwest Forest and Range Experiment Station|Forest Service, U.S. Department of Agriculture, Portland, Oregon, USA, are available on the web.

Calculations
To calculate the amount of sunlight reaching the ground, both Earth's elliptical orbit and the attenuation by Earth's atmosphere have to be taken into account. The extraterrestrial solar illuminance (Eext), corrected for the elliptical orbit by using the day number of the year (dn), is given to a good approximation by;
E_{\rm ext}= E_{\rm sc} \cdot \left(1+0.033412 \cdot \cos\left(2\pi\frac{{\rm dn}-3}{365}\right)\right),
where dn=1 on January 1st; dn=32 on February 1st; dn=59 on March 1st (except on leap years, where dn=60), etc. In this formula dn–3 is used, because in modern times Earth's perihelion, the closest approach to the Sun and, therefore, the maximum Eext occurs around January 3 each year. The value of 0.033412 is determined knowing that the ratio between the perihelion (0.98328989 AU) squared and the aphelion (1.01671033 AU) squared should be approximately 0.935338.
The solar illuminance constant (Esc), is equal to 128×103 lx. The direct normal illuminance (Edn), corrected for the attenuating effects of the atmosphere is given by:
E_{\rm dn}=E_{\rm ext}\,e^{-cm},
where c is the atmospheric extinction and m is the relative optical airmass. The atmospheric extinction brings the number of lux down to around 100 000.
Solar Constant
The solar constant, a measure of flux density, is the amount of incoming solar electromagnetic radiation per unit area that would be incident on a plane perpendicular to the rays, at a distance of one astronomical unit (AU), (roughly the mean distance from the Sun to Earth). The "solar constant" includes all types of solar radiation, not just the visible light. Its average value was thought to be approximately 1.366 kW/m², varying slightly with solar activity, but recent recalibrations of the relevant satellite observations indicate a value closer to 1.361 kW/m² is more realistic.


Solar irradiance spectrum at top of atmosphere, on a linear scale and plotted against wavenumber.

Total (TSI) and Spectral Solar Irradiance (SSI) Upon Earth
Total Solar Irradiance (TSI) – the amount of solar radiation received at the top of Earth's atmosphere – has been measured since 1978 by a series of overlapping NASA and ESA satellite experiments to be 1.361 kilowatts per square meter (kW/m²). TSI observations are continuing today with the ACRIMSAT/ACRIM3, SOHO/VIRGO and SORCE/TIM satellite experiments. Variation of TSI has been discovered on many timescales including the solar magnetic cycle and many shorter periodic cycles. TSI provides the energy that drives Earth's climate, so continuation of the TSI time series database is critical to understanding the role of solar variability in climate change.
Spectral Solar Irradiance (SSI) – the spectral distribution of the TSI – has been monitored since 2003 by the SORCE Spectral Irradiance Monitor (SIM). It has been found that SSI at UV (ultraviolet) wavelength corresponds in a less clear, and probably more complicated fashion, with Earth's climate responses than earlier assumed, fueling broad avenues of new research in “the connection of the Sun and stratosphere, troposphere, biosphere, ocean, and Earth’s climate”.
Intensity in Solar System
Different bodies of the Solar System receive light of an intensity inversely proportional to the square of their distance from Sun. A rough table comparing the amount of solar radiation received by each planet in the Solar System follows from data:
Planet or dwarf planet distance (AU)Solar radiation (W/m²)
PerihelionAphelionmaximumminimum
Mercury 0.3075 0.466714,446 6,272
Venus 0.7184 0.7282 2,647 2,576
Earth 0.9833 1.017 1,413 1,321
Mars 1.382 1.666   715   492
Jupiter 4.950 5.458    55.8    45.9
Saturn 9.04810.12    16.7    13.4
Uranus18.3820.08     4.04     3.39
Neptune29.7730.44     1.54     1.47
Pluto29.6648.87     1.55     0.57
The actual brightness of sunlight that would be observed at the surface depends also on the presence and composition of an atmosphere. For example, Venus's thick atmosphere reflects more than 60% of the solar light it receives. The actual illumination of the surface is about 14,000 lux, comparable to that on Earth "in the daytime with overcast clouds".
Sunlight on Mars is dimmer than on Earth. This photo of a Martian sunset was imaged by Mars Pathfinder.
Sunlight on Mars would be more or less like daylight on Earth during a slightly overcast day, and, as can be seen in the pictures taken by the rovers, there is enough diffuse sky radiation that shadows would not seem particularly dark. Thus, it would give perceptions and "feel" very much like Earth daylight. The spectrum on the surface is slightly redder than that on Earth, due to scattering by reddish dust in the Martian atmosphere.
For comparison purposes, sunlight on Saturn is slightly brighter than Earth sunlight at the average sunset or sunrise (see daylight for comparison table). Even on Pluto the sunlight would still be bright enough to almost match the average living room. To see sunlight as dim as full moonlight on Earth, a distance of about 500 AU (~69 light-hours) is needed; there are only a handful of objects in the Solar System known to orbit farther than such a distance, among them 90377 Sedna and (87269) 2000 OO67.
Surface Illuminations
The spectrum of surface illumination depends upon solar elevation due to atmospheric effects, with the blue spectral component dominating during twilight before and after sunrise and sunset, respectively, and red dominating during sunrise and sunset. These effects are apparent in natural light photography where the principal source of illumination is sunlight as mediated by the atmosphere.
While the color of the sky is usually determined by Rayleigh scattering, an exception occurs at sunset and twilight. "Preferential absorption of sunlight by ozone over long horizon paths gives the zenith sky its blueness when the sun is near the horizon".
See diffuse sky radiation for more details.
Spectral Composition of Sunlight and Earth Surface
The Sun's electromagnetic radiation which is received at the Earth's surface is predominantly light that falls within the range of wavelengths to which the visual systems of the animals that inhabit Earth's surface are sensitive. The Sun may therefore be said to illuminate, which is a measure of the light within a specific sensitivity range. Many animals (including humans) have a sensitivity range of approximately 400–700 nm, and given optimal conditions the absorption and scattering by Earth's atmosphere produces illumination that approximates an equal-energy illuminant for most of this range. The useful range for color vision in humans, for example, is approximately 450–650 nm. Aside from effects that arise at sunset and sunrise, the spectral composition changes primarily in respect to how directly sunlight is able to illuminate. When illumination is indirect, Rayleigh scattering in the upper atmosphere will lead blue wavelengths to dominate. Water vapour in the lower atmosphere produces further scattering and ozone, dust and water particles will also absorb selective wavelengths.

Spectrum of the visible wavelengths at approximately sea level; illumination by direct sunlight compared with direct sunlight scattered by cloud cover and with indirect sunlight by varying degrees of cloud cover. The yellow line shows the spectrum of direct illumination under optimal conditions. The other illumination conditions are scaled to show their relation to direct illumination. The units of spectral power are simply raw sensor values (with a linear response at specific wavelengths).
Seasonal and Orbital Variation
On Earth, the solar radiation varies with the angle of the sun above the horizon, with longer sunlight duration at high latitudes during summer, varying to no sunlight at all in winter near the poles. When the direct radiation is not blocked by clouds, it is experienced as sunshine. The warming of the ground (and other objects) depends on the absorption of the electromagnetic radiation in the form of heat.
The amount of radiation intercepted by a planetary body varies inversely with the square of the distance between the star and the planet. Earth's orbit and obliquity change with time (over thousands of years), sometimes forming a nearly perfect circle, and at other times stretching out to an orbital eccentricity of 5% (currently 1.67%). As the orbital eccentricity changes, the average distance from the sun (the semimajor axis does not significantly vary, and so the total insolation over a year remains almost constant due to Kepler's second law,
\tfrac{2A}{r^2}dt = d\theta,
where A is the "areal velocity" invariant. That is, the integration over the orbital period (also invariant) is a constant.
\int_{0}^{T} \tfrac{2A}{r^2}dt = \int_{0}^{2\pi} d\theta = \mathrm{constant}.
If we assume the solar radiation power P as a constant over time and the solar irradiation given by the inverse-square law, we obtain also the average insolation as a constant.
But the seasonal and latitudinal distribution and intensity of solar radiation received at Earth's surface does vary. The effect of sun angle on climate results in the change in solar energy in summer and winter. For example, at latitudes of 65 degrees, this can vary by more than 25% as a result of Earth's orbital variation. Because changes in winter and summer tend to offset, the change in the annual average insolation at any given location is near zero, but the redistribution of energy between summer and winter does strongly affect the intensity of seasonal cycles. Such changes associated with the redistribution of solar energy are considered a likely cause for the coming and going of recent ice ages (see: Milankovitch cycles).
Solar Intensity Variation
Space-based observations of solar irradiance started in 1978. These measurements show that the solar constant is not constant. It varies on many time scales, including the 11-year sunspot solar cycle. When going further back in time, one has to rely on irradiance reconstructions, using sunspots for the past 400 years or cosmogenic radionuclides for going back 10,000 years. Such reconstructions have been done. These studies show that in addition to the solar irradiance variation with the solar cycle (the (Schwabe) cycle), the solar activitiy varies with longer cycles, such as the proposed 88 year (Gleisberg cycle), 208 year (DeVries cycle) and 1,000 year (Eddy cycle).

Life on Earth
The existence of nearly all life on Earth is fueled by light from the Sun. Most autotrophs, such as plants, use the energy of sunlight, combined with carbon dioxide and water, to produce simple sugars—a process known as photosynthesis. These sugars are then used as building-blocks and in other synthetic pathways that allow the organism to grow.
Heterotrophs, such as animals, use light from the Sun indirectly by consuming the products of autotrophs, either by consuming autotrophs, by consuming their products, or by consuming other heterotrophs. The sugars and other molecular components produced by the autotrophs are then broken down, releasing stored solar energy, and giving the heterotroph the energy required for survival. This process is known as cellular respiration.
In prehistory, humans began to further extend this process by putting plant and animal materials to other uses. They used animal skins for warmth, for example, or wooden weapons to hunt. These skills allowed humans to harvest more of the sunlight than was possible through glycolysis alone, and human population began to grow.
During the Neolithic Revolution, the domestication of plants and animals further increased human access to solar energy. Fields devoted to crops were enriched by inedible plant matter, providing sugars and nutrients for future harvests. Animals that had previously provided humans with only meat and tools once they were killed were now used for labour throughout their lives, fueled by grasses inedible to humans.
The more recent discoveries of coal, petroleum and natural gas are modern extensions of this trend. These fossil fuels are the remnants of ancient plant and animal matter, formed using energy from sunlight and then trapped within Earth for millions of years. Because the stored energy in these fossil fuels has accumulated over many millions of years, they have allowed modern humans to massively increase the production and consumption of primary energy. As the amount of fossil fuel is large but finite, this cannot continue indefinitely, and various theories exist as to what will follow this stage of human civilization (e.g., alternative fuels, Malthusian catastrophe, new urbanism, peak oil).
Cultural Aspects
The effect of sunlight is relevant to painting, evidenced for instance in works of Claude Monet on outdoor scenes and landscapes.


Claude Monet: Le déjeuner sur l'herbe.
Many people find direct sunlight to be too bright for comfort, especially when reading from white paper upon which the sun is directly shining. Indeed, looking directly at the sun can cause long-term vision damage. To compensate for the brightness of sunlight, many people wear sunglasses. Cars, many helmets and caps are equipped with visors to block the sun from direct vision when the sun is at a low angle. Sunshine is often blocked from entering buildings through the use of walls,window blinds, awnings, shutters, curtains or nearby shade trees.
In colder countries, many people prefer sunnier days and often avoid the shade. In hotter countries, the converse is true; during the midday hours, many people prefer to stay inside to remain cool. If they do go outside, they seek shade that may be provided by trees, parasols and so on.
Winter sunshine
In Hinduism the sun is considered to be a god as it is the source of life and energy on earth.
Sunbathing
Sunbathing is a popular leisure activity in which a person sits or lies in direct sunshine. People often sunbathe in comfortable places where there is ample sunlight. Some common places for sunbathing include beaches, open air swimming pools, parks, gardens and sidewalk cafes. Sunbathers typically wear limited amounts of clothing or some simply go nude. For some, an alternative to sunbathing is the use of a sunbed that generates ultraviolet light and can be used indoors regardless of weather conditions. Tanning beds have been banned in a number of states in the world.
For many people with light skin, one purpose for sunbathing is to darken one's skin color (get a sun tan), as this is considered in some cultures to be attractive, associated with outdoor activity, vacations/holidays and health. Some people prefer naked sunbathing so that an "all-over" or "even" tan can be obtained, sometimes as part of a specific lifestyle.
For people suffering from psoriasis, sunbathing is an effective way of healing the symptoms.
Skin tanning is achieved by an increase in the dark pigment inside skin cells called melanocytes and is an automatic response mechanism of the body to sufficient exposure to ultraviolet radiation from the sun or from artificial sunlamps. Thus, the tan gradually disappears with time, when one is no longer exposed to these sources.
Effects on Human Health
The ultraviolet radiation in sunlight has both positive and negative health effects, as it is both a principal source of vitamin Dand a mutagen. A dietary supplement can supply vitamin D without this mutagenic effect, but bypasses natural mechanisms that would prevent overdoses of vitamin D generated internally from sunlight. Vitamin D has a wide range of positive health effects, which include strengthening bones and possibly inhibiting the growth of some cancers. Sun exposure has also been associated with the timing of melatonin, synthesis, maintenance of normal circadian rhythms, and reduced risk of seasonal affective disorder. 
Long-term sunlight exposure is known to be associated with the development of skin cancer, skinaging, immune suppression and eye diseases such as cataracts and macular degeneration. Short-term overexposure is the cause of sunburn, snow blindness, and solar retinopathy.
UV rays, and therefore sunlight and sunlamps, are the only listed carcinogens that are known to have health benefits, and a number of public health organizations state that there needs to be a balance between the risks of having too much sunlight or too little. There is a general consensus that sunburn should always be avoided.
References

  1. ^ "Chapter 8 – Measurement of sunshine duration". (PDF)CIMO Guide. World Meteorological Organization. Retrieved 2008-12-01.
  2. ^ "NASA: The 8-minute travel time to Earth by sunlight hides a thousand-year journey that actually began in the core". NASA, sunearthday.nasa.gov. Retrieved 2012-02-12.
  3. ^ "Introduction to Solar Radiation".  Newport Corporation. Archived from the original on Oct 29, 2013.
  4. ^ Calculated from data in "Reference Solar Spectral Irradiance: Air Mass 1.5". National Renewable Energy Laboratory. Archived from the original on Sep 28, 2013. Retrieved 2009-11-12. The first of each set of two figures is for total solar radiation reaching a panel aimed at the Sun (which is 42° above the horizon), whereas the second figure of each pair is the "direct plus circumsolar" radiation (circumsolar meaning coming from the part of the sky within a couple degrees of the Sun). The totals, from 280 to 4000 nm, are 1000.4 and 900.1 W/m2 respectively. It would be good to have more direct figures from a good source, rather than summing thousands of numbers in a database.
  5. ^ Calculated from the ASTM spectrum cited above.
  6. ^ Qiang, Fu (2003). "Radiation (Solar), (PDF). In Holton, James R. Encyclopedia of atmospheric sciences 5. Amsterdam: Academic Press. pp. 1859–1863. ISBN 978-0-12-227095-6. OCLC 249246073.
  7. ^ Appleton, E. V., Nature 3966:535 (1945)
  8. ^ Iqbal, M., "An Introduction to Solar Radiation", Academic Press (1983), Chap. 3
  9. ^ NASA Solar System Exploration – Sun: Facts & Figures, retrieved 27 April 2011 "Effective Temperature ... 5777 K"
  10. ^ http://www.nasa.gov/mission_pages/GLAST/news/highest-energy.html.
Further Reading

  • Hartmann, Thom (1998). The Last Hours of Ancient Sunlight. London: Hodder and Stoughton. ISBN 0-340-82243-0.

External Links
 Media related to Sunlight at Wikimedia Commons
  • Solar radiation – Encyclopedia of Earth
  • Total Solar Irradiance (TSI) Daily mean data at the website of the National Geophysical Data Center.
  • Construction of a Composite Total Solar Irradiance (TSI) Time Series from 1978 to present by World Radiation Center, Physikalisch-Meteorologisches Observatorium Davos (pmod wrc)
  • A Comparison of Methods for Providing Solar Radiation Data to Crop Models and Decision Support Systems, Rivington et al.
  • Evaluation of three model estimations of solar radiation at 24 UK stations, Rivington et al.
  • High resolution spectrum of solar radiation from Observatoire de Paris.
  • Measuring Solar Radiation,  A lesson plan from the National Science Digital Library.
  • Websurf astronomical information: Online tools for calculating Rising and setting times of Sun, Moon or planet, Azimuth of Sun, Moon or planet at rising and setting, Altitude and azimuth of Sun, Moon or planet for a given date or range of dates, and more.
  • An Excel workbook with a solar position and solar radiation time-series calculator; by Greg Pelletier.
  • ASTM Standard for solar spectrum at ground level in the US (latitude ~37 degrees).
  • Detailed spectrum of the sun at Astronomy Picture of the Day.

- Wikipedia 

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