Here is a Basic Guide to
Blacklight Sources and Fixtures.
THE FOLLOWING MAY NOT BE REPRODUCED
WITHOUT PERMISSION FROM THE AUTHOR ©
The incandescent source is an ordinary light bulb or `R' type floodlamp with a dark purple coating. These lamps fail to give off much in the ultraviolet (UV) frequency range because so little UV is radiated from these sources at that end of the spectrum. The incandescent blacklignts typically have a short life - usually only a few hundred hours. Also, some types hold in a great deal of heat and thus can become dangerously hot to the touch.
For stage or club use, these are not recommended except as a purple light bulb. Home users may get a small effect if the source is placed close to a blacklight poster. However, given the short life, possible excessive heat, and the better effect from even a small fluorescent source, these lamps are not recommended to anyone except those on the smallest budgets. Even then, the glow effect will disappoint.
The fluorescent source is the most popular and the cheapest overall when it comes to creating glowing effects for the performance industry. It emits ultraviolet rays by striking an arc within a vapour of mercury. By eliminating the fluorescent coating on the lamp's glass wall, UV escapes to the outside. The harmful, shorter rays are stopped by the ordinary glass that make up the bulk of the fluorescent tube.
Wattages range from 6 to 40 watts with sizes ranging from compact source, through T8 up to T12 bulb diameters. The compact 15- or 20-watt sources are recommended only for home use, except for sign or point lighting where a small fixture at close range will suffice. The 40-watt, T12 lamps, especially in pairs or quads, are required for stage or large area lighting. Be aware that 32-watt, T8 blacklight tubes are now available as replacements.
Home users can expect an excellent effect from the less expensive, 15-watt, T8 lamps. Life is much greater than the incandescents: Typically 7,500 to 9,000 hours for the lower wattage lamps, on up to over 20,000 hours from the 40 watters.
Be aware that off brands typically last far fewer hours, and usually do not give as much UV per watt. Also, the cheaper lamps often have poorer filters and allow much more visible light through. This dilutes the effect greatly. So be sure the tubes have the `BLB' (Blacklight Blue) lamp designation and that these have quality filters. One way to tell is to view the tubes during operation; the better filters show a deeper purple colour. Even with this though, test to see that the UV output is still high by comparing tubes placed at the same distance in a dark room as each shines on to an object that fluoresces under blacklight. A deeper purple may only mean lower UV output.
Mercury vapour lamps are a larger version of the fluorescent source both of which operate using the mercury arc principle. They come in small PAR 38 sizes on up to the large 400 watt models. Some have the UV filter right on the lamp, while others use an external filter on the fixture itself. These lamps are recommended for large stage productions. They are expensive but can place very high levels of UV into an area. The disadvantage is that they can take up to seven minutes to reach full output, as opposed to the other sources discussed here which are instant on, or nearly so, depending on the lamp and ballast or power supply used.
In all cases, be sure to buy dark, filtered sources. They block up to 80% of visible light emitted by the lamp. Using non-filtered sources is cheaper, but it's the equivalent of having a white light on, thus the effect is diluted.
Light Emitting Diodes employed for ultraviolet purposes are relatively new on the market. LEDs emit light in a narrow range of frequencies, so the UV LED radiates in the near ultraviolet range and thus will cause fluorescent materials to glow.
To have enough output for stage usage, banks of LED elements are arrayed in rows. Look for consistancy among the elements. Each should output at the same level as the others in the fixture and as those in adjacent fixtures. Each element should be colour consistent within the array, and each should not vary its colour or abruptly lose intensity as one views from off axis. In addition, check to see how well materials fluoresce. Cheaper UV LEDs don't radiate far enough into the UV range, so items may not glow as brightly. A clue is that these LEDs radiate too much visible purple light.
Another criterion may be shielding, depending on your intended purpose. Although not as wide as fluorescent sources, LED elements do radiate over a fairly wide angle. This may not be what you want, so look for units that can accept barndoors, or that limit the horizontal and vertical beam angles by having the elements well recessed from the front of the fixture.
Germicidal lamps are NEVER to be used for entertainment lighting. They radiate much shorter wavelengths of UV that are meant to kill bacteria, so skin and eyes would be harmed if exposed to a germicidal lamp's rays.
The incandescents and PAR 38 mercury vapour lamps use a medium screw base socket. Mercury vapour lamps also require a ballast fixture, as do fluorescents. The ballast is in part a transformer/coil used to start the lamp and control current through it. When buying a ballast fixture, it must be a Sound Rated `A'. These emit low audible noise and also transmit less noise into audio systems, which are often used near these lights. The LED unit has a built-in power supply that provides the correct voltage to each element.
For the wide-angle sources, a fixture with a white enamel or polished reflector is usually what is required. These direct/reflect the light towards your intended area and control spill to some extent. Fixtures with a black reflector may look nice but they reduce the potential intensity of blacklight rays striking fluorescent objects, and thus diminish the effect.
Larger mercury vapour fixtures come with an integral ballast and typically a 250-watt lamp. They use a larger-diameter filter at the front of the fixture and give a high intensity, wide-coverage beam. Some lamps come already filtered. These can be used in most any suitable fixture designed for mercury vapour lamps. The disadvantage to these lamps is that they take 4 - 7 minutes to come up to full intensity.
LED arrays come in their own fixtures. For stage usage, select one that is rectangular for wide coverage, and try to find ones with some sort of sides or barndoors that control spill. This is so as to not fluoresce unwanted objects on or off the stage. Look for higher wattage LEDs so as to have maximum UV output.
Blacklights and Supplies
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