UV filtering glass for HQI

[Delphinus]

+1 .. this isn't rocket science ... no need to make it harder than it has to be. If you really don't trust the glass then don't use DE lamps. Done and done.

Originally Posted by sphelps

Like I said "Low E" (low-emissivity) glass, it filters the most UV with it's special coating. It's not expensive and all glass shops will have it, if you don't want to spring for the tempering just go up to 5mm and you should be fine.

Otherwise use SE bulbs.

[midgetwaiter]

Originally Posted by sphelps

Like I said "Low E" (low-emissivity) glass, it filters the most UV with it's special coating. It's not expensive and all glass shops will have it, if you don't want to spring for the tempering just go up to 5mm and you should be fine.

Otherwise use SE bulbs.

There is a couple mistakes here.

First I'm pretty sure standard "Low E" is designed to block infrared not UV, I'm not sure it will block UV at all but it probably does. However I'm thinking trapping the infrared a mh bulb puts out in the pendant might not be a good thing for your bulb life.

Standard plate glass will block > 95% of UVB which is why you won't tan behind glass windows. It won't block hardly any UVA though which has been shown to have nasty effects on connective tissue. There does exist a type of glass that has a mixture of SO2 on Ti02 on it that will block UVA as well as UVB, it is used in cars sometimes and you can probably find it somewhere. So given that everyone assumes we need to rush out and buy glass that blocks UVA and UVB to cover our DE bulbs so they're safe. This is Wrong.

A common mistake is to assume that the glass envelope on a SE bulb filters out all the UV produced by the the bulb, It doesn't. If you look at the link to Dana Riddle's article posted by scuglass you will see that they were measuring the UVA and UVB output of SE bulbs. There are plenty of people here using SE bulbs without additional shielding in addition to the outer envelope to good effect so what gives? The answer is that we are not necessarily concerned with blocking all of the UV that comes off of a DE bulb, only the wavelengths that are especially dangerous. These wavelengths are primarily the shorter UVC wavelengths and probably a good portion of the UVB as well, regular float glass will do this. In fact a DE bulb behind float glass probably puts out less UVB than a SE bulb.

The cheapest way to get a chunk of tempered 5mm glass for your pendant is probably to go buy an outdoor halogen fixture at Home Depot or something and just use the glass. Halogen bulbs require the same shielding as DE mh bulbs do.