quartz (Silicon di-oxide, SiO2) with a high melting
point and excellent UV transmissivity is used in
fabrication of UV processor lamps. A 22 x 25 mm
diameter tube with wall thickness of 1.0 to 1.5
mm used with tungsten electrodes sealed into each
end is typical. Lamps are manufactured from 1"
to 180¡± arc length. Quartz is very fragile and special
cushioned packaging is utilized for safe transportation.
Upon receiving new lamps the carton should be opened
fully so the lamp can be lifted out of the packaging
with no twisting or pulling. Unpacking should take
place in an area large enough to eliminate the possibility
of inadvertently striking lamp against walls, pillars,
pipes, beams, or machinery. Lamp must be wiped with
alcohol before placing in service. Bare skin contact
with the quartz envelope must be avoided. Compounds
from the skin when heated on lamps operating at
600o to 850o C will form permanent etching (devitrification)
on the quartz surface, decreasing UV energy transmission.
A contaminated lamp eventually will overheat causing
light from lamps should not be visible and bounce
(reflected) light should be minimized and avoided.
Medium pressure UV lamps radiate harmful UV which
can cause serious burns to skin and eyes. While
thermal burns are felt immediately, UV burns are
not felt for several hours. Short exposure to
lamp radiation can cause severe burning of skin
and eyes. UV burn of the eyes affects the cornea
and takes several days to heal. UV burn is identical
to "Welder's burn" and will feel like
sand in the eyes that cannot be washed out. The
discomfort is transitory. Extreme caution must
be taken - high power UV radiation can cause blindness.
Limited exposure to UV radiation will evoke erythema
on normal skin. Such erythema is transitory and
will not produce blistering, nor tanning, as only
a small amount of radiation penetrates the Malpighian
layer. Extreme caution must be taken since, high
power UV radiation can cause severe burns to the
Handling UV lamps
carton should be opened fully so lamp can be lifted
out of packaging with no twisting or pulling.
Unpacking should take place in an area large enough
to eliminate the possibility of inadvertently
striking lamp against walls, pillars, pipes, beams
or press machinery.
Lamp must be wiped with alcohol before placing
in service. Bare skin contact with the quartz
envelope must be avoided. Compounds from the skin
when heated on lamps operating at 600 to 850C
will form permanent etching (devitrification)
on the quartz surface decreasing UV energy transmission.
A contaminated lamp eventually will overheat causing
oxygen or ozone (O3) is the only byproduct of
the UV lamp. It is formed by oxygen being exposed
to 254nm wavelengths of UV energy. Ozone formation
can be eliminated by using ozone-free quartz lamps.
Certain dioxides which absorb the ozone producing
wavelengths are added to the quartz of these lamps.
Ozone-free and pure fused quartz lamps are interchangeable.
Ozone-free lamp usage may affect cure speeds if
ink or coating formulation is designed to utilize
the absorbed wavelengths.
A nitrogen atmosphere in a processor also eliminates
ozone production by eliminating oxygen. Lower
power lamps may be used in a nitrogen atmosphere;
however, the cost of nitrogen will probably offset
any operating cost savings attained.
Ozone can be effectively eliminated in the processing
area by exhausting air from the cooling system
of the UV processor to outside the building. Such
exhausting involves no danger as the hot gas is
very unstable and breaks down to oxygen rapidly
in ducting. Neither a nitrogen atmosphere or ozone-free
lamps eliminate the cooling system required by
lamps and related UV processor components.
energy, an inherent product of the arc utilized
to create UV energy in UV processors, can cause
overheating of processor components when adequate
safeguards are not incorporated into the UV processor
design and application. Cooled heat sinks should
provide protection to the press, conveyor, and
other process components in or near the UV processor.
The cooling system should be carefully designed
and properly maintained. In air-cooled systems,
filters must be properly cleaned or replaced on
a maintenance schedule related to powder, dust,
and dirt conditions where the UV processor is
operating. Halon #1211 fire extinguishers are
to be used in the event of fire. CO2 fire extinguishers
with dry chemical or water are NOT recommended.
If a fire occurs, all residue of damaged substrate
should be removed from curing area. Soot and ash
must be cleaned from lamps and reflectors before
re-start. Investigation to determine the malfunction
causing the fire is most important. Correction
must be made to eliminate re-occurrence. UV processor
electrical systems should be serviced only by
To most, cooling of the lamp is usually perceived
to be one of the least important factors in the
function of the UV curing system, but in fact
it is one of the most important. UV lamp is made
of quartz because this is the only material that
transmits UV-light and at the same time endures
high temperatures of 6 to 800¡ÆC.
Each UV system was intended to function in a
certain temperature range and when the temperature
falls out of this range the lamps will degrade
at a much faster rate. On many systems the blower
has a baffle to regulate airflow to the UV lamp,
hence regulating temperature. When this baffle
is closed too much the lamp will tend to overheat,
which is usually seen when the lamps become distorted
in shape and end fillings and wire possibly showing
signs of extreme heat. On the other hand when
the baffle is open too much the lamp may be overcooled,
this will show when the ends of the lamp turn
dark black. Both of these conditions are detrimental
to the life of the lamp.
Longer UVA wavelengths emitted by black lights
and general purpose high pressure mercury lamps
are basically harmless. Although the hazard is
not quite zero, it is generally quite negligible.
The same is generally true of any UV-containing
light that has passed through ordinary glass.
There is an exception: Some drugs photosensitize
skin to ordinarily harmless quantities and wavelengths
of UV. Ask your doctor or pharmacist.
Shorter UVA wavelengths cause suntanning. It
is widely believed that UV suntanning is not completely
safe no matter what you do. Possible ill effects
include skin cancers and accelerated aging of
UVB is much worse, inherently irritating. The
skin is designed to take small amounts of UVB
and recover, but nothing is perfect here. You
probably want to avoid any significant UVB exposure
unless a physician recommends UVB exposure for
UVC is even worse, but less penetrating since
it is easily absorbed. The outermost portion of
human skin is made of dead cells. This layer sometimes
gives partial protection from UVC, especially
shorter wavelengths. However, don't count on this.
UVC is quite damaging to living cells and has
nasty burning effects.
UVA has one nasty effect on eyes, known as "nuclear
cataracts". This is a permanent "tanning"
of the lens of the eye. "Nuclear" refers
to this occurring mainly in the center of the
lens of the eye. You need heavy exposure to get
this. Nuclear cataracts occur mainly among people
who work outdoors. Although incandescent black
lights emit wavelengths that cause nuclear cataracts,
they are largely safe since you typically get
less UV exposure from these than from sunlight.
Even considering the fact that your pupils are
wider under black light than under sunlight, there
is so much less UV that it is safe to stare into
the bulb from a few feet away for large amounts
Fluorescent black lights are worse, but are usually
comparable to sunlight when you are a couple feet
away. Although I have yet to hear of eye damage
blamed on reasonable use of black lights, those
who are around them a lot may want UV blocking
Persons who have had cataract surgery need extra
protection, since the lens of the eye largely
absorbs UV. The retina does not like strong exposure
to UV. It should be noted that UVA-related eye
damage involves a process with at least two steps.
The first step (excitation of tryptophan or related
molecules) normally reverses itself. Damage requires
excited molecules to receive additional UV before
they de-excite. This means that UVA eye damage
is not linearly proportional to the intensity
of exposure, although it may be proportional to
the duration of exposure of a given intensity.
I have yet to see data indicating clearly what
is and is not safe. However, nuclear cataracts
are most common in people who work outdoors in
sunny areas. In case of doubt, use UV blocking
eyewear. Cheaper amber and yellow sunglasses do
actually work - I have tested them. Sunglass lenses
made of real glass and green in color attenuate
UV a fair amount. Clear, blue, purple, or pink
glasses may not work, even if they are claimed
to work. I saw one pair of clear glasses with
a sticker claiming "100 percent UV blocking"
which let through more UV than window glass did.
UVB is worse on eyes than UVA, and can burn the
cornea and the conjunctiva. UVC is especially
burning to the conjunctiva. Please beware that
symptoms are delayed considerably from exposure.
Symptoms typically begin a few minutes after exposure
and gradually increase for at least a half an
hour, often an hour to a few hours after exposure.
If you have been exposed and any symptoms begin,
promptly seek emergency medical care to minimize