Viewing the Sun through light-concentrating optics such as binoculars is very hazardous without an appropriate filter that blocks UV and substantially dims the sunlight. An attenuating (ND) filter might not filter UV and so is still dangerous. Attenuating filters to view the Sun should be specifically designed for that use: some improvised filters pass UV or IR rays that can harm the eye at high brightness levels. Unfiltered binoculars can deliver over 500 times as much energy to the retina as using the naked eye, killing retinal cells almost instantly (even though the power per unit area of image on the retina is the same, the heat cannot dissipate fast enough because the image is larger). Even brief glances at the midday Sun through unfiltered binoculars can cause permanent blindness.

Partial solar eclipses are hazardous to view because the eye’s pupil is not adapted to the unusually high visual contrast: the pupil dilates according to the total amount of light in the field of view, not by the brightest object in the field. During partial eclipses most sunlight is blocked by the Moon passing in front of the Sun, but the uncovered parts of the photosphere have the same surface brightness as during a normal day. In the overall gloom, the pupil expands from ~2 mm to ~6 mm, and each retinal cell exposed to the solar image receives about ten times more light than it would looking at the non-eclipsed Sun. This can damage or kill those cells, resulting in small permanent blind spots for the viewer. The hazard is insidious for inexperienced observers and for children, because there is no perception of pain: it is not immediately obvious that one’s vision is being destroyed.

During sunrise and sunset sunlight is attenuated due to Rayleigh scattering and Mie scattering from a particularly long passage through Earth’s atmosphere, and the Sun is sometimes faint enough to be viewed comfortably with the naked eye or safely with optics (provided there is no risk of bright sunlight suddenly appearing through a break between clouds). Hazy conditions, atmospheric dust, and high humidity contribute to this atmospheric attenuation.

A rare optical phenomenon may occur shortly after sunset or before sunrise, known as a green flash. The flash is caused by light from the Sun just below the horizon being bent (usually through a temperature inversion) towards the observer. Light of shorter wavelengths (violet, blue, green) is bent more than that of longer wavelengths (yellow, orange, red) but the violet and blue light is scattered more, leaving light that is perceived as green.

Ultraviolet light from the Sun has antiseptic properties and can be used to sanitize tools and water. It also causes sunburn, and has other medical effects such as the production of vitamin D. Ultraviolet light is strongly attenuated by Earth’s ozone layer, so that the amount of UV varies greatly with latitude and has been partially responsible for many biological adaptations, including variations in human skin color in different regions of the globe.

• A four-star rating system that informs consumers how well the product protects them against “Ultraviolet A” (UVA) light.

• Information on other ways people can limit their risks to dangers posed by overexposure to sunlight.

What do “UVA” and “UVB”stand for?

UVA and UVB are types of ultra­violet (UV) radiation emitted by the sun. Although the atmosphere’s ozone layer shields us from most of this radiation, the UV light that gets through can cause problems. UVB light is primarily responsible for sunburn. UVA light penetrates the skin more than UVB light does, and causes tanning. Both types of UV light contribute to premature skin aging, skin cancer, and other types of skin damage..

Currently, sunscreen labels are required to carry a “Sunburn Protec­tion Factor” (SPF) value that informs potential users how well the product protects against UVB light.

The Four-Star System.

Under the proposed regulation, a UVA star rating would be promi­nently displayed on sunscreen labels, near the SPF rating..

“For more than 30 years, consum­ers have been able to identify the level of UVB protection provided by sunscreens using only sunburn protection factor or SPF values,” said Andrew C. von Eschenbach, M.D., Commissioner, Food and Drugs. Under this proposal, “consumers will also now know the level of UVA protection in sunscreens, which will help them make informed decisions about protecting themselves and their children against the harmful effects of the sun.”

With the proposed UVA rating system.

• One star will represent low UVA protection
• Two stars, medium protection
• Three stars, high protection
• Four stars, the highest UVA protection available in an over-the-counter (OTC) sunscreen product.
• If a sunscreen product does not rate at least one star, FDA is proposing that its labeling bear a “no UVA protection” marking on the front label, near the SPF value.

Sunscreen Not the Only Option.

In addition to the new rating system, FDA wants sunscreen labels to advise consumers that using a sunscreen is just one way they can protect them­selves against the sun. Limiting time in the sun and wearing protective clothing as part of a comprehensive sun protection regimen are other rec­ommendations that would be promi­nently displayed on labels. Using sunscreens liberally and reapplying frequently would also be advised.

Changes With SPFs, Too.

FDA also wants to make changes regarding protection against UVB light. The agency has proposed amending its existing rule on UVB products to increase the maximum sunburn protection factor from SPF 30+ to SPF 50+.

The proposed rule is asking the pub­lic to comment on the use of nanopar­ticle ingredients in sunscreens, and is proposing to

• make minor changes in SPF (UVB) testing procedures consistent with current science, to further enhance the accuracy of SPF values.
• allow new combinations of active ingredients.