Skunking is a photochemical reaction. It only needs the presence of photons in visible light to cause the reaction. Blue light, and to a lesser extent green and a bit of near ultraviolet are the most damaging to beer.
Most wavelengths of ultraviolet light are not a concern because glass blocks them quite effectively (that’s why you don’t get sunburned in your car).
The brighter the light and the longer bottles sit in that light the stronger the skunky smell will be. Even dark brown bottles won't guard a beer from the bright fluorescent lights for very long.
The hop compounds that are responsible for making beer bitter are called isomerized alpha-acids. These chemicals, along with sulfur compounds found in beer, are also culpable in beer skunking. When light hits beer, it provides the energy necessary to drive a reaction that transforms the iso-alpha-acids into 3-methyl-2-butene-1-thiol. The “thiol” part of that name indicates that there is sulfur present. Sulfur compounds often have strong, offensive aromas. Skunks, have evolved the ability to produce this chemical, and use it for self-defense.
In a sense, the aroma of light-struck beer doesn’t just resemble skunk spray, it is skunk spray!
John
