What are Reactolite Spectacles?
Photochromic’s are usually referred to as “Reactolite” which is a brand name for the glass variety or “Transitions” which is a brand name for the plastic variety. Basically they do the same thing. These are lenses which are clear indoors but then “react” to UV (Sunlight) and “transform” into sunglasses.
NOTE: As photocromic lenses require UV to change, using them behind a car windscreen will not work as effectively as normal due to the windscreen filtering out some of the UV. However, we have found that the glass reactolite works better than the plastic behind a car windscreen, but not as good as the plastic in normal conditions.
Polychromatic is simply the generic term for a glass that adjusts to light levels. Reactolite is a brand name made popular by the Reactolite Rapides.
Reactolite is the name most people associate with this type of lens and a lot of people use the term in much the same way we call facial tissue "kleenex", it is in fact the trade name of one particular type of photochromic lens.
This lens was first produced as a spin off from the space race in the 60’s but it has now evolved far past its early forms. It is a lens that changes from light to dark and back again depending on the light it is in.
Although it was originally only available in glass, plastic versions have become available over the last few years. Some of the original plastic versions performed quite poorly and had some ‘interesting’ colours.
Now you can have faster reacting, less temperature dependent lenses in a choice of colours, including some that work just as well behind a car windshield - not all photochromics are the same.
The more UV (Sunny) they go darker. These are available in glass from such companies as Zeiss, and Pilkington (Reactolite Rapide) and plastic Transitions material. Care should always be taken with selection of sunglasses. As cheaper sunglasses which don't absorb UV will actually offer less protection than not wearing any sunglasses at all. As the dark lenses will cause the pupil to dilate and offer the harmful rays a larger window in which to penetrate the eyeball.
A wide range of sunglasses are available including such brands as Moschino, Ray Ban, Calvin Klein, Police, CK, Guess, Dolce & Gabbana and Nina Ricci. All of these offer 100% UVA and UVB absorption. Even more essential nowadays with the gradual depletion of the ozone layer, which used to filter out a lot of the harmful rays.
The lenses are made from toughened glass, plastic or polycarbonate. Some also have Anti Reflection coatings which help create a clearer sharper image by reducing ghost images.
Lenses can be made in two materials Organic (Plastic) or Mineral (Glass). Most lenses sold today are of the Plastic variety as they are far lighter than glass and safer due to strength and shatter resistence. Most people think that when we say a 1.6 lens that this means it is going to be 1.6mm thick, this is wrong. Basically the higher the number the thinner the lens will be.
Photochromic glasses dangerously reduce night vision
A worrying finding from investigation into a UK shipping accident is that photochromic glasses block so much light that they should not be used by ship's lookouts. The report on the loss of the yacht Ouzo and its crew of three, found that the lookout on the ship Pride of Bilbao, which collided with it, was wearing "reactolite" (photochromic or photoctomatic) prescription spectacles. These darken in reaction to ultra violet (UV) in daylight. At night these appear clear, but actually block 20% of the light (ordinary coated lenses only block 0.6% of the light). Perhaps there should be clearer warnings against the use of these lenses for other night activities, such as driving a car, or flying an aircraft.