UV protection glass

[pvtschultz]

Wait a second, tempering is a physical state and not a chemical state. Tempering will help it resist thermal shock if it should be splashed by a bit of water or cool unevenly, but it has nothing to do with the amount of UV Radiation it can filter out. It just so happens that they use it around these lights a lot for there better thermal properties. I really don't believe that you are going to filter out any more UV with the tempered glass than you will with tempered.

THere is also the idea that wild corals are subjected to UV on a constant basis and they seem to do alright. I have also read that filtering out too much of the UV will reduce coloration among other things. . You probably made a very rapid change when the bulbs were switched. But the corals did die back very quick...RTN?

 

[BeanAnimal]

The SUN and your MH bulb are two different animals with regards to UV. Also the wild corals are found in much deeper water where UV penetration is much reduced.

Glass tempering changes the structure of the glass surface. The molecules align in tight crystaline groups, and I am somewhat sure that this effects the way light is transmitted through the glass. A am sure a google search will provide some numbers one way or the other.

Bean

 

[pvtschultz]

Bean, it seems that you and I bunt heads on occasion and I by no means mean any harm by my comments. I have on the other hand studied radiation transmission recently and have a good idea as to what is going on inside the glass. On the other hand that doesn't mean that I am not wrong fully or partially.

Anyways, the process by which radiation (from gamma rays to near UV) is a molecular one of the individual atoms and not how the molecules are aligned. When electro-magnetic radiation passes through a substance, its wave length determines how it will react. The so called greenhouse gasses react with IR radiation on a molecular level and alter their vibratory energy, releasing thermal energy. As the wave lengths get shorter, they react with smaller things. For instance, gamma rays will free electrons from a material (this is where Einstein's E=mc^2 comes into play). Glass is partially transparent to near UV but opaque to the UVB's and UVC's. From Wikipidia:

Ordinary glass partially blocks UVA (wavelength 400 and 300 nm) and totally blocks UVC and UVB (wavelengths shorter than 300 nm) due to the addition of compounds such as soda ash (sodium carbonate).

Pure SiO2 glass (also called fused quartz) does not absorb UV light and is used for applications that require transparency in this region, although it is more expensive.

I did not find anything that mentioned the altering of emissivity of glass due to tempering, nor did I find anything to the contrary. So whether or not tempering improves the UV resistance of glass is speculation on our parts. What we do know is that glass does filter out most UV radiation and the application of tempered or float glass may be a functional/mechanical one moreso than a filtering one.

Personally, I would use tempered if possible, but you would have to buy it is a precut size. Any altering of the glass must be done before it is tempered otherwise it will shatter in the millions of pieces that we all know all too well from those trying to drill tempered aquariums.

 

[BeanAnimal]

I never said I was right or wrong either.. I just offered some input as to what may or may not be going on. I certainly hope my post was not viewed as confrontational. I would like to know more about how the tempering changes the light transmision characteristics of the glass myself, but just didn't have the time to look into it. Tempered glass appears different when viewed through a polarized filter. To me that menas that it's transmission characteristics are different than that of standard float glass.

I would agree that the tempered glass may be more of a mechanical consideration with regards to the UV we are worried about. Most "light plants" (the things you see lighting up construction or nightime highway projects) have MV or MH bulbs and UV shields. I have broken a few over the years, some tempered, some not.

Yup, no such thing as cutting tempered glass.

FWIW I have an order going in this week for a piece of 1/4" tempered charcaol black glass 23 X 40 with 3 holes drilled for hinges. I was quoted around $50. So I imagine a small 6x10 piece of clear tempered would be ~$10 at most.

LOW E glass would be another consideration. However I am again not sure what wavelengths it would filter. It would surely get more of the UV (by design) but I don't knwo what else.

 

[BeanAnimal]

As far as stacking the glass... I think we would both agree that the added interfaces cause a significant loss.