require a specific output or consistency between bulbs. Consequently, new bulbs can vary by as much as
50% in their initial output. This means that with two new bulbs, one may have an intensity that is
double that of the other without either being defective. New black light bulbs SHALL be tested for
output before being used. Intensity of new bulbs SHALL be at least 1000 µw/cm2 at a distance of 15
inches from the outside face of the filter.
b. Line Voltage Variations. Black light intensity varies almost linearly with line voltage. A common
misconception is that the black light ballast or transformer will regulate line variations. This is not
true. Below approximately 90 volts, the lamps will not sustain the mercury arc and the lamp will
extinguish. It will not restart until it has cooled. Black light lamps should be connected to stable power
sources. If none are available and line voltage fluctuates, a constant potential transformer should be
c. Service and Aging Variations. During use, dust and dirt will collect on both the bulb face and filter.
Even small amounts will reduce the intensity and, if allowed to build up, can result in a 10-fold
decrease. The bulb face and filter SHALL be kept clean. The output of black light bulbs will vary due
to changes in operating characteristics. As the bulb ages, the intensity will gradually decrease.
Operating hours will decrease output. Of greater significance is the number of bulb starts. A single
start can equate to 2 or 3 hours of continuous use on operating life. Black lights that will be used
periodically during the day should be allowed to remain on until their last use of the day. This practice
will extend the useful bulb life.
Black Light Hazards.
Prolonged direct exposure of hands to the filtered blacklight main beam may be
harmful. Suitable nonfluorescent gloves SHALL be worn when exposing hands to
the main beam for extended periods (e.g.: exceeding two hours per day).
The temperature of some operating black light bulbs reaches 750°F (399°C) or more
during operation. This is above the ignition or flash point of fuel vapors. These
vapors will burst into flame if they contact the bulb. These black lights SHALL
NOT be operated when flammable vapors are present.
The bulb temperature also heats the external surfaces of the lamp housing. The
temperature is not high enough to be visually apparent, but is high enough to cause
severe burns with even momentary contact of exposed body surfaces. Extreme care
must be exercised to prevent contacting the housing with any part of the body.
Black Light Physiological Effects.
Unfiltered ultraviolet radiation can be harmful to the eyes and skin. Black light
bulbs SHALL NOT be operated without filters. Cracked, chipped, or ill-fitting
filters SHALL be replaced before using the lamp.