The sun emits light at wavelengths all across the electromagnetic spectrum. Two major components of sunlight are visible light and ultraviolet light (UV). Each has important but very different effects on our health.

Bright Light

Here are some medically proven benefits and facts of bright light:

  • Light therapy is just as effective as antidepressant medication for both seasonal depression (SAD) and nonseasonal depression.
  • Light therapy works more quickly than antidepressant medication in relieving symptoms of both seasonal and nonseasonal depression.
  • Light therapy is an effective treatment for many sleep disorders.
  • Geographical regions with more sunshine have less ADHD.
  • Light therapy improves function in Parkinson’s Disease.
  • Light therapy improves sleep and decreases both agitation and depression in Alzheimer’s Disease.
  • Light is proven to improve wakefulness and decrease stress.

Visible light (or bright light) is the portion of the electromagnetic spectrum that our eyes can “see.” The rod and cone (visual) receptors of our retina respond to those wavelengths.

In 2000, another type of receptor was discovered in the retina, a “non-visual” receptor, which also responds to light in the visible spectrum but does not contribute to sight. Instead, these receptors stimulate the suprachiasmatic nucleus of the brain (SCN), which controls our body’s clock (circadian rhythm), regulating our sleep, energy, alertness, and mood. Our visual retinal receptors respond to very low levels of light. We can even read by the light of a single candle. Our non-visual retinal receptors need the brightness of the rising sun to tell us that the day is starting. That brightness is what we mean by “bright light.”

Put most simply: bright light enters your eyes and wakes up your brain. It works through the eyes, not the skin, so you can be covered in clothing or sunscreen from head-to-toe and still get all of bright light’s health benefits.

There is no restricted “maximum” for your daily bright light, but you should avoid it before bed. You know when you’re on your iPad late at night, and you turn it off and try to immediately go to sleep, but you can’t? That’s because the light produced from the iPad has tricked you brain into thinking it’s still day! (Those non-visual receptors are particularly sensitive to the blue light of our digital displays, and unfortunately, we hold our screens very close to our eyes.)

Getting the right amount of bright light during the early part of the day (and avoiding it late at night) is pivotal for your physical and mental health.

For more information, read our white paper on the health benefits of bright light.

Ultraviolet (UV) Light

UV light is invisible to the human eye and does not affect circadian rhythm. Its most important effects on health come from absorption by your skin, not through your eyes. The health benefits (and warnings) for UV and bright light are quite different.

UV light is essential for our body’s production of vitamin D (see Vitamin D section). Yet the absorption of UV light by the skin is also associated with suntan, sunburn, long-term skin damage and skin cancer. Note that the best time to get your bright light is early in the morning, when the UV component of sunlight is lower.

Long-term exposure of the eyes to UV light can also be associated with an increased risk of cataracts. UV radiation in sunlight is highest during the mid-day hours (10AM - 2PM). All prescription glasses in the US protect against UV light without reducing the brightness of visible light. Most sunglasses also protect against UV light, while reducing visible light to around 25% of what the naked eye would see. The brightness of the sun near mid-day is far above the amount required for maximal health benefit, so SunSprite can still let you know when you’ve had your right dose even if you’re wearing sunglasses.

SunSprite accurately measures the real-time UV intensity and provides a user with an easy guide to stay safe in high UV levels. For instance, when the UV index is 4, you will see “A UV Index reading of 3 to 5 means moderate risk of harm from unprotected sun exposure.” And if UV is 12, you will see: “A UV Index reading of 11 or more means extreme risk of harm from unprotected sun exposure. Take all precautions because unprotected skin and eyes can burn in minutes.”

If you wish to avoid any possibility of UV exposure while getting the full benefits of bright light, you can either receive your bright light through a window or purchase a therapeutic light box. SunSprite lets you move around when you use a light box and still be sure that you have received the right the “dose” of light.

Tanning beds are just the opposite – UV exposure without the visible light. There is no good reason to visit them.

Vitamin D

Vitamin D is essential for our health. Vitamin D3 is produced in the skin when exposed to UV light. Long understood as important for bone health, adequate levels of vitamin D have more recently been associated with reduced risks of cardiovascular disease and some types of cancer. It is difficult to get enough vitamin D from our diet and, in higher latitudes during the winter, perhaps impossible to get enough vitamin D from sunshine.

Here are the current NIH recommendations on sun exposure and vitamin D:

Ten to 15 minutes of sunshine three times weekly is enough to produce the body's requirement of vitamin D. The sun needs to shine on the skin of your face, arms, back, or legs (without sunscreen). Because exposure to sunlight is a risk for skin cancer, you should use sunscreen after a few minutes in the sun.

Because production of vitamin D is affected by skin type as well as sun exposure, doctors often test for vitamin D blood levels and recommend supplements when they are low. Some evidence suggests that vitamin D supplements do not give the same benefits as vitamin D from food or sunshine.

SunSprite does not currently track vitamin D intake, but future software updates will have vitamin D tracking.