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Ultraviolet Light and Black Light: a beginner's guide
by David Rudd Cycleback


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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(3)
The different categories of UV
light, including black light

 

Ultraviolet light itself is commonly divided into categories. As with all light, the sections are defined by the wavelength.

The most common categories you will see are UVA (also known as longwave UV and black light), UVB (a.k.a .mid-wave UV) and UVC (a.k.a. shortwave UV and germicidal light).

 

Common names:
UVA = longwave UV = blacklight
UVB = midwave UV
UVC = shortwave UV = germicidal light

 

Measuring and representing ultraviolet light: wavelengths.
Light is represented and measured in different ways. The most common way is to represent it is as waves. Length of the wave is measured from crest to crest, though you can also measure it bottom to bottom.

Wavelength is commonly measured in nanometers (abbreviated as nm). A nanometer is one billionth of a meter, or one millionth of a millimeter. A human hair is roughly 30,000 nm thick. One will occasionally find light represented in Angstroms (A), which is one tenth (1/10th) of a nanometer. An easy conversion.

1 nanometer = 10 Angstroms
1 Angstrom = 0.1 nanometer

The following are the wavelengths in nanometers for UVA, UVB and UVC:

UVA (longwave, blacklight) = 320 to 400 nm
UVB (mid-wave)= 280-315nm
UVC (shortwave, germicidal) = 200-280 nm

Most black lights, including the one you use for this book, are in the 380s-390s nm range. This is just a tad longer in wavelength than visible violet light.

Most germicidal lamps are 254nm. Germicidal light is dangerous for human skin and eyes, but is stopped by ordinary glass and even clothing.

Other names and ranges of UV light:

** Near UV: 400 nm - 300 nm (This includes blacklight, and black light is sometimes called Near UV)
** Far UV: 200 nm - 122 nm 6
** Vacuum UV: 200 nm - 10 (Vacuum UV light is absorbed by air and must be used in a vacuum.)
** Extreme UV: 121 nm - 10 nm
** Deep Ultraviolet: 300 and below

Note that different people sometimes categorize ultraviolet light differently, in particular giving different names to the categories and giving a category a different range of wavelengts. Usually the variations are only slight. For example, one person may say the edge of black light is 400nm, while another says its 380. Some people call black light longwave UV or Near UV. As long as you look the wavelength of the light (ala, this book recommends using blacklight in the about 370-390 nm), the variations used should not be a problem.

 

Next: Your tool for this guide: a black light

 

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