View Full Version : Could a super-bright light cause blindness?
02-15-2012, 08:50 AM
Just a little refinement on your answer to question about a super bright light causing blindness. Actually it is the ultraviolet light that causes the damage. Yes, if you are close enough the heat would fry you. But if we are just talking about light, then no, it can't cause blindness just by the intensity.
Richard Feynman, the great physicist knew this, and during the first nuclear bomb test he declined the welders glasses and watched through a car windshield because he new that would block the UV light and protect his eyes. He was right and suffered no ill effects. He claimed he was likely the only person who actually saw the blast without the dark glasses.
02-15-2012, 10:39 AM
If that were true (only UV causes damage), then why do lasers have warnings not to look at them? Light after all is energy and will cause heating in anything that absorbs it, including your retina, which can be damaged at relatively low temperatures. I'm pretty sure that sunlight, even without UV, is intense enough to cause damage, judging by how hot a sunlit surface can get. Here (http://ijt.sagepub.com/content/21/6/473.abstract) is an article that explores the causes of retinal damage, which can be thermal, photochemical or even mechanical:
If the rate of energy deposition is too low to produce an appreciable temperature increase in the tissue, then any resulting tissue damage necessarily occurs because of chemical (oxidative) reactions induced by absorption of energetic photons (photochemical damage). If the rate of energy deposition is faster than the rate of thermal diffusion (thermal confinement), then the temperature of the exposed tissue rises. If a critical temperature is reached (typically about 10° C above basal), then thermal damage occurs. If the light energy is deposited faster than mechanical relaxation can occur (stress confinement), then a thermoelastic pressure wave is produced, and tissue is disrupted by shear forces or by cavitation—nonlinear effects.
Also, I am assuming that you were referring to this article (http://www.straightdope.com/columns/read/669/do-crystals-have-special-powers) (which blames infrared for the damage caused by atomic explosions, although the article was talking about light intense enough to cause instant blindness).
02-23-2012, 08:35 AM
There was a ship that exploded in an American harbour during ww2 and some people who witnessed it was struck blind. I'm not sure which bandwidth would have been emitted, but I'm guessing UV and IR would have been somewhat limited at range from a conventional HE explosion.
I'm not sure what mechanism would be involved though.
I'll see if I can track down the incident.
02-29-2012, 07:07 AM
That article is from 1989, there are tools being used by police and special forces such as flash grenades or more recently the Dazer Laser (http://en.wikipedia.org/wiki/Dazer_laser) which render their victims temporarily blind, but there is evidence of permament damage.
The differentiation is that flash blindness oversaturates(bleaches) the retina while photokeratitis (http://en.wikipedia.org/wiki/Photokeratitis)caused by UV exposure is akin to sunburn of the retina.
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