Absorption Chart
Material % of UV B Absorbed % of UV A Absorbed
Clear crown glass 79% 20%
Clear Plastic 100% 90%
UV-coated plastic 100% 100%
Polycarbonate 100% 99%
Transitions Plus 100% 99.5%
Ultraviolet light is broken into two categories by ANSI.
UV A is considered from 315nm to 380nm and UV B from 290nm to 315nm. While ANSI does not classify 380nm to 400nm as ultraviolet, there is some concern that there may be some damage caused by light in this range. If there is a concern about this, hard resin lenses can have a UV tint applied to them that will absorb light in this range, however, as 380nm is the beginning of the visible spectrum, these lenses oftentimes have a slight yellow tint.
As you can see, clear lenses, regardless of what type of material is used, filter some of the ultraviolet light present. The amount depends on the type of material. The best ultraviolet absorption is obtained by adding an ultraviolet absorbing tint to a plastic lens. This type of tint will absorb nearly 100% of UV B and nearly 100% of UV A. They will also absorb nearly all of the light from 380nm to 400nm.
The term blue light transmittance is defined in the ANSI standard as transmittance of optical radiation, weighted by its ability to cause photo chemical damage to the retina. In this context, blue light is that part of the visible spectrum from 400nm to 500nm. While this part of the spectrum is not generally considered harmful in the amount found in sunlight, if it occurs in intense amounts from an artificial source, such as from a welding arc, it can be harmful. The amount of blue light hazard peaks at about 435nm. When an individual is exposed to this type of blue light appropriate filtering lenses must be used.
The following definitions, taken from ANSI Z87.1-1989 may be helpful:
- Optical Radiation is defined to be that portion of the electromagnetic spectrum with wavelengths between 200 and 2000 nanometers.
- Blue-light transmittance is the transmittance of optical radiation weighted by its ability to cause photo chemical damage to the retina.
- Luminous transmittance (light that produces the sensation of light) is the fraction of light (380-780nm) passing through a medium. This is commonly referred to as visible light.
- Infrared radiation, as related to the ANSI standard, is electromagnetic energy with wavelengths from 780 to 2000 nanometers.
- Ultraviolet radiation, as related to the ANSI standard, is electromagnetic energy with wavelengths from 200 to 380 nanometers.
It is important to understand that there is a clear distinction between glasses with some form of tint designed to make the wearer more comfortable in regular lighting situations, and eyewear designed to protect the eye from a very specific source of hazardous radiation. There are a wide variety of devices developed to protect the eyes from most sources of hazardous radiation. Most are designed for a specific use, so it is imperative that you clearly understand the uses and limitations of each device.
CAUTION: Many such lenses offer inadequate ultraviolet and/or infrared protection. Caution shall be exercised in their use for each application, and the responsible individual shall ensure that the proper ultraviolet, infrared and visible protection is provided. For example, a lens may provide ample ultraviolet protection in some situations but not in others.
The ANSI describes many special purpose tints for specific needs. If you have any questions regarding what tint to use for a specific application, please contact the Essilor Laboratories Inside Sales Office.