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UV lamps typically come in both portable models and as permanent display units, offering one or more wavelengths depending on the model. The basic elements of a UV lamp include the power source, the ultraviolet light bulb, and the filter.
While a typical permanent display lamp runs off house current, a portable lamp is powered by batteries, some of which are rechargeable, depending on the model. Often times, more expensive portable lamps are also configured with an AC adapter to run off of house current.
UV light bulbs are constructed of a special high silica glass, or of quartz in the finest quality. They are rated by wattage, not unlike a bulb in your house lamp, so this can be an indication of your lamp's brightness. However, this is not a hard and fast rule because the way in which a UV lamp is powered and designed also affects its brightness. Shortwave bulbs appear clear when off. Longwave bulbs, having phosphors on the inside, with or without integral filters, appear white or black (blacklight) when turned off.
Along with ultraviolet light, all UV lamps emit some visible light, too, which tends to mask any fluorescence, so special dark purple glass filters are placed over the bulb to block the visible light, while allowing as much UV light to still pass through. Longwave filters, which have a relatively coarse surface appearance, last indefinitely.
Shortwave filters, which often have highly polished surfaces, will deteriorate over time from exposure to the very Shortwave light they are filtering, a process called solarization. Long exposure to humidity will also damage Shortwave filters. After about 1 to 5 months of continuous use, the filter's transmission drops to about 25%, so your mineral collection, for instance, will not fluoresce as brightly. Thus, a Shortwave filter should be replaced when spent.
In contrast to the life of Shortwave filters, UV light bulbs last a very long time. However, the phosphors in a Longwave bulb can deteriorate with time, so if your Longwave fluorescence appears dull, you may want to replace the bulb. If your Shortwave fluorescence is dull, replace your filter before replacing the bulb because the bulb will withstand the effects of solarization perhaps 50 times longer than will the filter.
Keep in mind that the darker your surrounds, the easier it will be to observe the effects of fluorescence from your UV lamp. Depending upon how bright your lamp is, you may or may not be able to use it in the daylight.