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Dear Dr. Vinny,

In a previous question, you recommended putting UV-protective film on a wine refrigerator to further protect it from sunlight. Is UV blocking enough? Or does the amount of visible light transmission (VLT) matter too?

—Jason, Washougal, Wash.

Dear Jason,

Most wine coolers come with some sort of ultraviolet (UV) light protection on their glass doors. Even if it looks clear to you, it might still be blocking harmful UV rays. Keep in mind that UV light is that electromagnetic radiation that comes from things like the sun, tanning lamps and black lights. UV rays can harm a person’s skin, eyes, as well as degrade polymers and dyes, and can certainly have a negative effect on a bottle of wine.

When you start looking for protective films to put over cellar glass, you might come across the term VLT (Visible Light Transmission). The percentage of VLT refers to the amount of light that is allowed to pass through. A film with 10 percent VLT will block 90 percent of the light, only allowing 10 percent to come through. The lower the number, the more concentrated the tint.

VLT and UV measure two different things--even though there’s an obvious relationship between visual light and ultraviolet light. But UV-blocking technology can be more specific, with particular coatings and molecules that can absorb light waves before they become damaging.

This was a really long way of saying that I think that your move to further increase the light protection of your wine is a terrific idea. There’s no one formula of how much light over how much time equates to a particular amount of damage (or not). But any additional light protection might help, and it certainly won’t hurt.

—Dr. Vinny

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