The next issue that comes up is the type of filter glass used; Hoya U 325 is hands down the best filter glass for short and mid emission. In an effort to keep our products affordable we are always looking at sourcing reliable components that will save you money. For Long wave filter emission we use Kokomo U 400 glass. This has been measured by us using a UV meter and does a fantastic job filtering the “white light”. Some may disagree but we frankly do not see a difference. It can be deceiving as the Kokomo has a rippled texture so you see what appears to be a variance in emission but it has not measured a substantial difference in our testing. The best of the best is to go with all Hoya and then have the ability to change the tubes and customize your own lamp fixture. Hoya will transmit all wavelengths. This will cost more but I believe that it is worth it. Some manufactures use a 2 mm filter glass that is just not adequate for this hobby. I have received many calls regarding Ebay purchases that have disappointed customers. At the end of the day it is generally the lamp not the rock!
Why do we need filter glass?
All of the easily available UV sources emit white light along with the UV. This white light interferes with looking at the fluorescent colors and it makes the colors look washed out or faded. The filter glass blocks the white light while letting the majority of the UV pass through the filter. The best SW filter glass available is made by Hoya of Japan. However, transmitting SW UV is not easy. Hoya glass will only transmit about 64% of the SW UV when the glass is new. As the glass is exposed to long term UV C, the UV C transmission decreases until the filter eventually needs to be replaced. The LW glass on the other hand passes about 85% of the LW UV and never needs replacing.
The SW bulb has Hoya SW filter glass. The LW bulb has the much less expensive LW filter glass. The LW filter glass will only pass about 60% of the MW, while the SW glass will pass about 90%. You could switch the SW bulb with a MW bulb, but I do not think you would be happy with the MW bulb behind the LW glass. However, I can make the lamps with any combination of parts. The SW glass WILL work with the either the LW OR the MW bulb, so it is possible to use TWO pieces of SW glass in building a lamp fixture, but it adds to the cost because of the difference in the cost of the SW glass vs. the LW glass.
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