UV lamps

You need an UV-lamp to light up fluorescent minerals. Most used are fluorescent tubes.

The UV-light we use with fluorescent minerals can be divided into three categories:

UV-A , UV-B and UV-C (Extreme-UV also exists but we don’t practically use that with fluorescent minerals).

On our planet we have UV-A light in abundance from the sun. It is not being stopped by the atmosphere and passes through glass with ease.

UV-B light passes through the atmosphere by a small amount and it hardly passes through glass.

UV-C light does not penetrate the atmosphere and doesn’t reach the earth surface.

UV-light is visible to the eye for a small portion of the spectrum. This portion is in the UV-A area until approximately 380nm. Below that UV light is invisible to the human eye.

UV-C light and fluorescence is widely used all around us in fluorescent lighting.

Almost all fluorescent tubes generate UV-C light on the inside of the tube. This UV hits a layer of fluorescent powder on the inside of the tube which in turn generates the white light we see.

There are also fluorescent tubes which excite UV-A, UV-C or UV-C light

UV-A tubes work just as normal fluorescent tubes. They’re also made of ordinary glass with the difference that the powders (fosfors) on the inside of the tube convert the UV-C light to UV-A light

There are 2 types of UV-A tubes:

“black” tubes, also known as black lights. The exact description of these lamps is actually: Black light Blue (BLB).

These type of black lights are widely used in discotheques and for detecting counterfeit money.

“white” tubes, also known as actinic types. The exact description of these lamps is Blacklight (BL).

These type of tubes are often used in bug zapping lamps.

Besides UV-A these tubes also generate a lot of visible light. This visible light is not desirable for fluorescent minerals and needs to be filtered out with a special black filter glass

UV-B and UV-C tubes are made of special glass that passes this light. Normal glass only passes UV-A and can’t be uses for UV-B and UV-C.

For UV-B and UV-C pure silica glass is used. This type of glass is also used in laboratory. It’s evident that this glass is much more expensive

With UV-B tubes there’s a powder (phosphors) on the inside of that converts the UV-C light to UV-B light. There is also a lot of visible light being generated and that must be filtered out with a special filter

This filter is also made of pure silica and made black for the visible spectrum with special additions.

Only UV-light passes through these filters. These filters are very expensive and together with the more expensive UV-B makes this part of displaying fluorescent minerals expensive.

Only a few suppliers in the world make this type of filterglass and the best performing type what Colorgems uses is Hoya U325C.

UV-C tubes are also made of pure silica glass without any powders (phosphors) inside, so the tubes are transparent.

The mercury vapor inside generates the 254nm emission and that only needs to pass through the glass. Unfortunately mercury also has spectral lines which generate visible light that needs to be filtered out.

These filters are the same as for the UV-B lamps and Colorgems also uses Hoya U325C for these UV-C lamps.