How do they make black lights?
Just as there are different kinds of light bulbs that give
off visible light, there are different kinds of lights that give
off black light. As you will see in this chapter, black lights
are simply variations on regular lights. The most common black
lights are fluorescent, incandescent and LED (light emitting
diode).
The following looks at the different kinds of visible lights
and the black lights variations.
Visible light incandescent light
The incandescent visible light is the traditional screw
into the light socket that people have used for years and years.
It is the light bulb Thomas Edison invented.
The incandescent light is comprised of a filament, a base
(the metal screw in end) and the glass bulb. The filament is
a thin wire inside the bulb the electricity goes through. The
electricity heats up the filament to a degree that it gives off
the light that we see. A bad side effect of the incandescent
light bulb is it gives of great heat, as anyone who's burned
her fingers while unscrewing a light bulb can attest. This also
shows that it is an inefficient user of electricity, giving off
about as much heat as light.
Incandescent black lights cover a normal visible incandescent
with wood's light. Wood's light lets black light through while
blocking most visible light. These aren't quite as good at producing
black light as the fluorescent version and, as with all incandescent
lights, get hot.
Visible light fluorescent light:
Many homes and offices use fluorescent lights. They usually give
of whiter than incandescent light, make a hum and do not give
off heat. They are often in long or 'curlicue' tubes.
A fluorescent light has a glass tube filled with mercury and
argon gas. Electricity going through the bulb causes the gas
to give off ultraviolet light. The ultraviolet light hits phosphors
that coat the inside of the bulb, causing the phosphors to give
off the light we see.
Fluorescent black light. Most black lights are fluorescent.
These use a different type of phosphor to coat the inside the
bulb. It also covers the tube or bulb with a dark blue/purple
Wood's glass. Wood's glass blocks out all but the black light.
Light emitting diodes (LED).
Light Emitting Diodes (LEDs) are semiconductor chips that can
be designed to emit different ranges of lights, including the
visible colors, infrared and black light. Visiable light LEDs
are used in many products, including stop lights, LED flash lights,
car and computer lights. Many television and VCR remote controls
have LED infrared lights. Some black lights sold to hobbyists,
including small flash lights, are LED.
assorted visible light LED lights giving
off different colors
Next: Practical and interesting
uses for your black light
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