Sunglasses and Tinted Lenses

Is there any need for sunglasses?

The human eye, under normal circumstances, has the ability to adapt from a dark room to brilliant sunshine. The only time, normally, when some protection is desired is:

(a) Driving for any period of time in hot sunny climates as protection against infra-red rays.

(b) On snow or ice or water, as ultra-violet rays are reflected off into the eye.

(c) Industrial needs.

However, quite often, most of us feel that some protection against glare would be useful. Hence, moderately tinted lenses, which decrease the light transmission, should suffice.

Should tinted glasses be worn all the time?

The normal eye needs no protection unless it is unduly sensitive to light. The irony is that a fair number of normal people having started on tinted lenses for no apparent reason, now cannot get off them, since their eyes have become sensitive to light. It is for this reason that, except for medical reasons, children should not wear any kind of tinted glass.

What colour sunglasses are useful?

The colour of sunglasses should match the occupation for which they are designed.

(a) Where there is a real excess of ultra-violet, as for example over water or snow, the pinkish or brownish tints work the best.

(b) In hot inland countries or when driving for long distances over hot arid areas, protection is required against excessive infra-red. The ideal colour is green or greenish tinge.

(c) As regular sunglasses, for intermittent use in the city, the pale-brown and pale-grey lenses are adequate. Again a note of caution. Use the lightest colour you feel comfortable with.

What colour is of no use as sun glasses?

(a) Blue—popular in Bombay as cooling glasses. They have poor absorption of infra-red rays. Though lighter tints cause no damage, it must be understood that they are purely for “show”.

(b) Yellow glasses—yellow tints have the advantage of reducing glare and increase the apparent difference between the red and the greens. They improve visibility on a cloudy or hazy day or in light fog and hence are used by hunters, pilots, tennis players etc. However, their use as night-driving glasses is fraught with danger as they reduce the ability to see and differentiate dark objects. Although they have their uses, they are not recommended as sunglasses.

What about the new “automatic sunglasses”? How do they help?

These “automatic” sunglasses are knows as photo-chromatic lenses and change their density (deepness of colour) on exposure to ultra-violet light.

Infra-red radiation for which sunglasses in tropical climates should be designed, however, reverses the darkening process and causes the colour to decrease or bleach.

Their maximum colour is obtained only in cold climates and the colour reduces by heating the lens; hence in excess heat, the colour will lighten rather than darken.

After repeated exposure to ultra-violet light, the lenses pick up colour permanently and even in the dark, remain moderately tinted.

The older lenses used to take quite some time to reduce their colour, once a wearer went out in the sun. The newer rapid reactor lenses change in seconds and are far better and safer.

They are thus most useful at a ski resort or at high altitudes with snow where they effectively control the ultra-violet radiation and due to the cold have a high efficacy for colour change.

However, they are not sunglasses for tropical countries as the infra-red absorption is low, and heat bleaches the colour, thus lightening the intensity and decreasing the effect of the glasses.

How good are plastic sunglasses? How to test sunglasses when buying?

Plastic sunglasses have one disadvantage in common, no matter what tint: they do not filter out the infra-red rays and are thus of no use when driving along a road under a hot sun.

Properly ground and moulded they have many advantages both optically, and, more especially, considering their lightness.

Plastic sunglasses fall into two categories—good and bad. The good lenses are costly and are excellent optical appliances. The bad ones commonly sold on street corners are a poor apology for glare glasses.

There are two simple tests: first, look at a lamp post across the street. While holding your sunglasses at arm’s length, move the sunglasses slowly from side to side, looking through each section. If the post distorts or breaks, the lenses are defective.

Secondly, look at the reflection of a tube-light in the plastic lenses. It should reflect the light crisply and clearly. A poor distorted reflection tells you of the poor quality of the sunglasses.



3 Comments

  1. Blocking damaging UV (associated with many eye disorders, skin cancer and skin aging) and HEV light (associated with macular degeneration and the general breakdown of epithelial cells) are the main reason for wearing sunglasses. Children should wear sunglasses the crystalline lens inside a child's eye is much clearer than an adults allowing for more damaging light to reach the back of the eye. If you protect a child's eye from sun damage now you could prevent blindness later.

  2. No reference to claims and only heresay material here. Article would be far better if references to studies backing up the info here was included.

  3. I have just had cataract surgery and have been advised to wear reactor lenses glasses. I am not sure I am happy with this as I feel colour will always be distorted i.e. Gloomy when out in bright light. I realise that protection from UV rays is important after surgery but as glare is also a problem I’m wondering if clip on sunglasses would be better combined with a UV coating on the lenses. I too am not happy with the idea of wearing reactors all the time as I have seen the effects they have on people who cannot function in bright light without them. Comments appreciated.

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