Light
Light is an electromagnetic radiation that is divided into various types some of which are not visible to humans.
Ultraviolet Rays (from ~100nm to 380nm)
Ultraviolet Rays (UV) are invisible and have a damaging effect on the eyes. UV radiation is particularly dangerous as it does not directly stimulate the sensory nerves and symptoms are delayed for between six and twelve hours. UV is divided into three categories:
- UVA (315-380nm) dangerous - causes ageing of the eye
- UVB (280-315nm) dangerous - causes sunstroke
- UVC (~100-280nm) very dangerous to the eye - but filtered by the ozone layer
Visible Light (from 380nm to 780nm)
Light visible to the human eye which is divided into the colours of a rainbow (visible spectrum)
- 380 - 450 nm violet
- 450 - 500 nm blue
- 500 - 560 nm green
- 560 - 600 nm yellow
- 600 - 640 nm orange
- 640 - 780 nm red
Infrared Rays (from 780nm to 2000nm)
Infrared radiation is often accompanied by a sensation of warmth and hence an awareness of the hazard. Any potential damage can therefore be avoided. However excessive exposure can cause eye damage.Glare
Sunlight is scattered by the atmosphere and our surroundings, with the blue part of the visible spectrum scattered the most. This affects colour perception reduces contrast and causes glare which in turn produces eyestrain and discomfort.Influential Factors To Exposure
The intensity of solar radiation depends greatly on several factors including:Geography - Latitude, Longitude and especially altitude as well as the time of year and time of day. In addition reflected light can be very hazardous as it multiplies the amount of UV light striking the eyes, with sand reflecting 17% of incident light, water 60% and snow 85%.
What To Do
- Ensure your eyewear absorbs 100% Ultraviolet radiation.
- Use eyewear with the appropriate tint for your environment: Polarised lenses are particularly effective at reducing glare from horizontal surfaces and are therefore useful for skiers and sailors etc.Yellow filters reduce the blue part of the visible spectrum and therefore increase contrast and reduce glare and are often used in low light situations. Rose colour tints enhance contrast especially on overcast days. Tints designed for golf filter out red and blue light but let green light in. The result is increased contrast in the green part of the spectrum, so objects on the course stand out more, these tints tend to be greenish.