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Ultraviolet Light and Black Light: a beginner's guide



1) Introduction

2) What is ultraviolet light?

3) The different kinds of UV light

4) Your tool for this guide: a black light

5) Where does ultraviolet light come from? How was it discovered? Why can't we see it?

6) How are black lights made?

7) Practical and interesting uses for your black light

8) Examining art and collectibles: Introduction

9) Identifying modern fakes of antique paper memorabilia

10) Identifying counterfeit US currency

11) Identifying alterations to art, collectibles

12) Examining cloth

13) Examining art glass

14) Making glow in the dark art and crafts

15) Protecting yourself from the Sun's UV

16) UV light in science and industry

 

 

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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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