for the exposure:
One of the things
which is both fascinating and frustrating about alternative photographic
processes that require exposure to UV as an exposure source is that
there are so many variables. Different light sources work in different
ways with different ways.
the sun is appealing because of its simplicity, availability and
power, it is also incredibly variable. Exposure times can vary
from hour to hour, location to location etc. and it can easily
be discarded as an effective source. However - with this source
no electricity is required so the process can be completed in
even the remotest of locations - and also it contains a complete
spectrum of UV which some emulsions respond to differently than
a UV lamp source.
Ultraviolet refers to all electromagnetic radiation with wavelengths
in the range of 10 to 400 nanometers, or frequencies from 7.5E14 to
The UVA range is wavelengths from 315 to 400 nanometers.
Wavelengths from about 345 to 400 nM are used for "Blacklight"
effects (causing many fluorescent objects to glow) and are usually
very slightly visible if isolated from more visible wavelengths. Shorter
UVA wavelengths from 315 to 345 nM are used for suntanning.
UVB refers to
wavelengths from 280 to 315 nanometers. These wavelengths are more
hazardous than UVA wavelengths, and are largely responsible for sunburn.
The ozone layer partially blocks these wavelengths.
Strangely, UVB lasers are considered less hazardous than UVA lasers, since UVB is
more easily absorbed by various fluids and tissues in the eye and
cannot reach the retina in significant amounts. UVB also does not
penetrate as deeply in the skin as UVA. However, the deadliest types
of skin cancer (malignant melanomas) start in the epidermis, an upper
layer of the skin. UVB is largely blamed for these cancers, although
shorter UVA wavelengths are considered possibly cancer-causing.
UVC refers to shorter UV wavelengths, usually 200 to 280 nM. Even shorter
wavelengths from 10 to 200 nM are usually considered separately as
"Vacuum Ultraviolet" since they are absorbed by air, although
these wavelengths are also considered a shorter range of UVC. Wavelengths
in the UVC range, especially from the low 200's to about 275 nM, are
especially damaging to exposed cells. Such shortwave UV is often used
for germ killing purposes.
There are fluorescent tubes that emit UV. The phosphor coating on
the inner surface of the tube absorbs the UVC emitted by the low pressure
mercury arc, and emits longer UV wavelengths. There are at least six
different UV-emitting phosphors used in fluorescent lamps.
One common lamp is the ""BLB" fluorescent lamp. The
tubing is made from a very deep violet-blue glass known as "Wood's
glass". The tubing is quite transparent to medium and longer
UVA wavelengths, and shorter visible violet wavelengths, and a fairly
broad range of infrared and the longest, least visible red wavelengths.
These tubes emit lots of UV mainly between 350 and 375 nanometers,
some of the 404.7 and dimmer 407.8 nM violet mercury lines, and just
enough of the blue 435.8 nM mercury line to have a basically blue
color when lit.
The "BLB" lamps are used for special effects due to their
ability to make fluorescent objects glow very brightly.
There is a less
common deep-blue-violet lamp with no phosphor and made with special
glass (maybe quartz) to transmit the 253.7 nM UVC (shortwave UV) mercury line. These lamps are generally used to make
fluorescent rocks glow.
There are UV
fluorescent lamps with glass not dyed to block visible light. This
includes the BL and the similar 350BL. These are often used to attract
insects into electric insect killers. The 350BL has a broader spectrum
peaking at a slightly shorter wavelength (350 nanometers) than the
BL does, and is supposedly more attractive to insects than the BL.
There are other
ultraviolet lamps such as UVB medicinal lamps and UVA suntanning lamps.
There are also
the similar fluorescent actinic lamps, producing long UV wavelengths
and/or visible violet. These are sometimes used in some special photographic
and printing processes. One of these is the 03, specializing in producing
visible violet light. The 03 is also used in reef aquariums with live
coral since coral utilizes violet and deep blue wavelengths. The 03
actinic will cause fluorescence of most fluorescent dyes, pigments
and paints other than ones which fluoresce blue.
are a range of UV tubes that can be fitted into a standard Fluorescent
fittings. These lamps are efficient and produce little heat.
350 black light
contain about half the UV of the Philips
TLK 40 W/ 10R
box with 5 Philips TLK lamps
fan in the back of the box
Switch on door as a safe guard turns the light off when the
door is opened
Blacklights - Edison Screw UV Lamps
are a cheaper option and easier to fit. They can simply be screwed
into a house hold desk lamp. However they are less efficient,
produce more heat, and the illumination is more uneven than
There are incandescent bulbs made with deep violet-blue bulbs
which largely filter out visible light. Longer UVA wavelengths get through the glass and are not blocked by the
dark colored filter dye. Most visible violet and some visible
blue, as well as a wide range of infrared and the longest, less
visible of visible red wavelengths. Some traces of other visible
wavelengths get through.
These bulbs are a convenient source of some UV to cause fluorescent
paints, dyes, and other substances and objects to glow. Most
of such fluorescent objects (especially magenta, red, pink,
orange, yellow, and green ones) also glow from visible violet
and blue light.
are quite safe, although it may not be a good idea to stare
into one from short distances for long periods of time. They
generally have hotter running filaments that last only about
500 hours or so.
Strahler TH 1007 - Mercury
(high pressure mercury) Blacklights
The high pressure mercury spectrum includes a strong cluster
of lines in the 355-356 nanometer range. Fixtures with Wood's
glass and ordinary mercury lamps are sometimes used as high
power blacklights. Some of these fixtures are known as "beehive
lamps" due to their appearance and the buzzing sound of
their ballasts. Beehive lamps are available from some theatrical
Miniature Fluorescent Blacklights
There are now 3 mm. diameter cold cathode fluorescent miniature blacklight
tubes. These come in lengths of 25, 50, and 100 mm. These are available
at All Electronics, (800)-826-5432 or http://www.allcorp.com.
Catalog numbers are UV-325 ($8.25), UV-350 ($8.50), and UV-3100 ($10.75).
These apparently require only a few mA at 200 to maybe 300 volts,
but substantially higher voltage may be necessary for starting.
All Electronics also sells inverters to drive these lamps and related
miniature fluorescent lamps (3 to 6 mm. diameter) from 12 volts DC.
A major manufacturer of these and miniature cold cathode fluorescent
lamps (CCFL) in general is JKL Lamps.
sells JKL products including blacklight CCFL lamps.
Tanning and Medical UV Lamps
Back to UV-emitting fluorescent lamps! There is a type that emits
wavelengths in the short end of the UVA range, and these are used
for suntanning. One brand of these lamps is "Uvalux".
There is even a UVB emitting fluorescent lamp, used for some special
medical treatments of skin. These lamps are used to confine the UV's
effects to outer portions of the skin, since UVB is more readily absorbed
and less penetrating than UVA is.
"RS" Reflector ("floodlamp") Sunlamps
These lamps resemble ordinary "indoor" floodlamps. They
contain a high pressure mercury arc tube and a tungsten filament used
as a ballast. When first started, the light is mainly incandescent
light, and these lamps are sometimes mistaken at first for ordinary
floodlamps. When the mercury lamp warms up, the green-bluish white
color of the mercury light is more apparent. The main UV spectral
lines emitted are the 365-366 nanometer UVA cluster which is nearly
useless for tanning and the 313 nanometer UVB cluster. Some weaker
but significant shorter UVB lines are present, as well as a weak UVA
line at 334.1 nM, in the tanning range.
Since these lamps rely mainly on UVB for tanning, they are more likely
to cause sunburn and skin cancer than UVA suntanning lamps (which
are not completely safe either). The instructions for one of these
RS lamps actually states that some sunburn is necessary in order to
get a tan from such lamps. UVB lamps are also particularly irritating
to downright harmful to eyes.
There are other high pressure mercury sunlamps. Many of these are
of the "Sperti" brand, and most of these have a bare arc
tube made of a special glass. A few have a smaller arc tube made of
quartz or a glass that is nearly pure quartz. These lamps use nichrome
wire, basically heating elements, as the ballast to limit current.
The larger glass arc tubes often have electrodes over an inch from
the ends of the arc tube, and the ends need some of the heat from
the resistive elements in order for all of the arc tube to get hot
enough to fully vaporize the mercury.
Like the RS lamps, these lamps rely mainly on UVB for tanning and
are quite harsh on human skin and eyes.