Sunwear and the science of light

Light is both a particle and a wave, it has healing energy and harmful energy, and it is so fast that it travels the 24,901 miles around the earth seven and one half times in one second.¹ In order for us to understand how to best manage light with sunglasses, we first have to understand some basic science of light.

Breaking down the light

Visible light is a part of the electromagnetic spectrum, which is composed of energized photons, a massless energized particle that travels in waves. The electromagnetic spectrum ranges from radio waves at the longest wavelengths, to visible light, to gamma rays at the shortest wavelengths. As the wavelength goes from longer to shorter, the energy level of the photons increases.

Only the portion of the electromagnetic spectrum called the visible spectrum stimulates the human eye.² Wavelengths in this part of the electromagnetic spectrum are measured in nanometers (nm), which are one billionth of a meter. Visible light ranges between 400nm to 700 nm.

Other parts of the spectrum are also important for our health, including the ultraviolet (UV) portion of the spectrum. UV rays are separated into three groups:

– UVC runs from 200 nm to 280 nm and is extremely hazardous to the skin and eyes. Fortunately UVC is blocked out by the protective ozone layer of the atmosphere.

– UVB has wavelengths from 280 nm to 315 nm. These rays cause sunburn and are linked to skin cancer. The cornea and most lens materials absorb these rays.³

– UVA is closest to the visible spectrum at 31 nm to 380 nm. Long-term exposure can lead to pterygium growth and is linked to cataract development.^4,5

Related: The growing green trend in optical

Portions of the visible light spectrum can also be damaging to our health. High-energy violet (HEV) light is often referred to as high-energy blue light. The extreme violet end of the spectrum (380 nm to 430 nm) is the highest energy visible light that reaches the retina. Long-term exposure is linked to retina damage, increasing the likelihood of macular degeneration.⁶ Short-wave high-energy blue light also creates scatter and haze, making objects appear somewhat blurry.⁷ Blue light in wavelengths from 430 nm to 465 nm is also linked to sleep deprivation and melatonin suppression.⁸

The human eye has three different light-detecting cells which function in higher (daytime) lighting levels. Each of these “cone” cells is sensitive to a different range of wavelengths (blue, green, or red). Because the human visual system extrapolates colors from what it detects at just three basic wavelengths, it can easily be fooled. By optimizing these specific wavelengths, better color perception and clarity can be achieved.⁹

The human eye in daylight conditions has peak sensitivity around 555 nm with all three cone cell types working together.⁹ By emphasizing this peak when managing light, we achieve the best clarity of vision.

Next: Dimensions of color

Dimensions of color

Color consists of complex wavelength information as the human eye converts the full spectrum of light into three value systems of primary colors in order to simplify processing and rendering of that information. The three color attributes or dimensions are:

– Hue: Basic colors, such as red, green, and blue

– Saturation: The vividness or dullness of the color

– Brightness: The lightness or darkness of the color

Controlling the transmission curve’s rise relative to wavelength, which determines hue, can enhance color perception. For example, allowing an even and generous amount of red to be transmitted results in a brighter, vibrant red. Maximum transmission of green at its peak value (555 nm) will result in a darker and enhanced green.

Colors can be made more vivid by controlling the purity of the transmission curve. By giving the curve’s shape an enhanced distinctness, saturation is improved. If the curve is not distinct, then colors will blend and become dull. Color enhancement and vividness can be achieved by increasing saturation. Some colors may require more saturation for greater balance and distinction.

Related: How digital devices are affecting vision

Greater color enhancement can be achieved by selective transmission of good colors and nontransmission, or absorption, of bad colors that are known to create color confusion. Yellow light transmits in a very short range between 575 nm to 585 nm; however, it is one of the most disruptive wavelengths and causes to the colors adjacent to it, red and green, to become less vivid. Allowing the right amount of red and green to transmit while absorbing yellow requires complex filters, but when achieved the result is a lens with the highest color enhancing properties that create a “wow” effect for the wearer.

The brightness we perceive is determined by the amplitude, or height, of the curve’s waves. Optimization of a specific color’s brightness can be achieved by managing the right amount of transmission. Increasing the transmission of a color relative to other colors will result in a lightening effect, and reducing a color’s transmission will result in a darkening effect.

Next: Science meets sunglasses

Science meets sunglasses

The old-school way of designing sunglass lenses was to spend some time at the tinting stations trying to come up with colors that appeared pleasant and were also comfortable to look through. Not too dark, not too light, and do you like gray or brown? Maybe green? This system was reasonable for producing lenses that suited the basic need of sunglasses-reducing the amount of light reaching the eye-but did not allow for the higher performance and protection that is now possible with technical advances.

By knowing the science and properties of light, optical engineers and scientists can design sun lenses that maximize performance, enhance vision for specific activities, and protect our eyes from damaging radiation. For example, in the last few years a number of products have entered the market advertising HEV-blocking properties. With the aging population, if we have products that can reduce levels of macular degeneration, that will have great value to our society by reducing blindness and vision impairment requiring additional caregivers.^6,10 Better still, what if that lens also reduced haze and blur, provided greater clarity of vision, enhanced color definition, and came in an impact-resistant material?¹¹ Wouldn’t you (and your patients) want that?

A great example of just such a sun lens is the Costa 580 lens. Besides absorbing 100 percent of UV to 380 nm, these polarized lenses feature multi-patented color-enhancing technologies for brighter colors and increased clarity, absorb the highest amount of HEV of lenses in its class (100 percent to 425 nm), enhance “good” blue colors, enhance green at peak sensitivity (555 nm), filter out harsh yellow light (580 nm), and enhances red and green colors. Other examples of lenses with color enhancing properties include Maui Jim’s PolarizedPlus2 and Serengeti’s 555NM in addition to newcomers Smith ChromaPop and Oakley Prizm. 

Old technology meets new technology

While the science of light will continue to advance as we learn more of how light behaves and how our visual system perceives light, it is great to know that we already have products in hand to give our patients better visual performance and protection than ever before available.

References

1. NASA. How “Fast” is the Speed of Light? Available at: https://www.grc.nasa.gov/www/k-12/Numbers/Math/Mathematical_Thinking/how_fast_is_the_speed.htm. Accessed 2/18/16.

2. NASA. What Wavelength Goes With a Color? Available at:  http://science-edu.larc.nasa.gov/EDDOCS/Wavelengths_for_Colors.html. Accessed 2/18/16.

3. World Health Organization. Ultraviolet radiation. Available at:  http://www.who.int/uv/faq/whatisuv/en/index2.html. Accessed 2/18/16.

4. World Health Organization. Health effects of UV radiation. Available at: http://www.who.int/uv/health/en/. Accessed 2/18/16.

5. American Optometric Association. Protecting Your Eyes from Solar Radiation. Available at: http://www.aoa.org/patients-and-public/caring-for-your-vision/uv-protection?sso=y. Accessed 2/18/16.

6. American Macular Degeneration Foundation. Ultra-violet and Blue Light Aggravate Macular Degeneration. Available at: https://www.macular.org/ultra-violet-and-blue-light. Accessed 2/18/16.

7. Blue Light Exposed. Available at: http://www.bluelightexposed.com/#bluelightexposed. Accessed 2/18/16.

8. National Sleep Foundation. A great night’s sleep can depend on the visual conditions in your bedroom environment. Available at: https://sleepfoundation.org/bedroom/see.php. Accessed 2/18/16.

9. Soffer BH, Lynch DK. Some paradoxes, errors, and resolutions concerning the spectral optimization of human vision. Am J Physics. 1999 Nov:67(11):946-953. Available at:http://www.phys.ufl.edu/~hagen/phz4710/readings/AJPSofferLynch.pdf. Accessed 2/18/16.

10. Zeiss Vision Care. Blue Light: the Good and the Bad. Available at: http://www.zeiss.com/vision-care/en_us/better-vision/understanding-vision/eye-and-vision/blue-light-the-good-and-the-bad.html. Accessed 2/18/16.

11. Costa Del Mar. Choosing A Lens Color. Available at: https://www.costadelmar.com/shop/sunglasses/technology. Accessed 2/18/16.