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For Your Eyes Only

The solar eclipse may be a great thing to see, but that doesn't mean you have to go blind for that. Ultraviolet and infrared radiation from the sun can do some serious eye damage in a short time. And just because you don't feel it doesn't make the damage, which could lead to blindness, any better.

Sunlight has for long been known to cause ageing of the outer layers of the eye and in the development of cataract. But what many people don't know is that looking directly into the sun, even with protection, leads to retinal burns because the eye passes on most solar radiation to the retina. The trouble owes its effect to a series of complex chemical reactions in the light-sensitive rod and cone cells. The products of this cascade damages cells, impairing their ability to react to light or destroying them altogether. The effect is most pronounced in the face of blue or green light but the light of longer wavelength heats up the layer beneath the retina, burning it.

All very good, then how does one view the eclipse?

For one, you can use a pin-hole camera. First make a small hole in one sheet of paper. Then stand with your back to the sun and hold the sheet up. Let the image of the sun coming through the sun fall on other sheet. You have a clear idea what the sun's doing till its disc is covered. Once the eclipse enters totality, you can take a direct look till the sun begins to come out from behind the moon. Then you can again return to the pin-hole method.

You can watch the reflection of the sun in some dark liquid too.

According to one expert in the area, B Ralph Chou of the School of Optometry, University of Waterloo, Canada, some of the better varieties of compact discs can be used for viewing if the aluminium coating is dense enough to just allow one to see the glowing filament of an incandescent light bulb.

Most CDs don't fall in the category. And the fact that they appear semi-transparent at normal room illumination levels makes them appear safe when they aren't.

Don't rely on dark photographic film, smoked glass, black transparencies, floppy disk media or any screen that you can just about see through. While the light you see may be blocked, there's no guarantee that invisible and dangerous UV and infra-red light isn't getting through. And don't even think of relying on sunglasses, no matter how exotic they may claim to be.

According to Ralph Chou, shade 12 and 14 welding filters, black polymer filters, two layers of fully exposed and developed silver-bearing black and white film negative do fit the bill.

Finally, there are specialised glasses made for solar viewing but do ensure that they have the backing of some regulatory authority and that there are no scratches on the surface.

Take care. Enjoy.

For more information on retinal burns and filter, check B Ralph Chou's Eclipse Safety Page