(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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