Download Frequently Asked Questions About OHP Lamps

Frequently Asked Questions About OHP Lamps
1. What effect does the high/low lamp switch (if equipped) have on light output
and lamp life?
The overhead projector will provide the advertised light output and average lamp life when the
high setting is used and, therefore, should be considered the “normal” setting. The low setting
will approximately double the lamp life, but will reduce the light output approximately 20%.
2. What is the difference between FNT and EHJ lamps?
The lamp construction appears similar. The FNT lamp is rated 24 volts 275 watts and the EHJ is
24 volts 250 watts. The FNT lamp provides an additional 25 watts or 10% over the EHJ lamp
wattage. This is approximately 20% more light output at the same lamp life rating. An EHJ
lamp can be used in place of an FNT lamp; however, in order to maintain screen performance we
do not recommend using EHJ lamps in overhead projectors designed to use FNT lamps.
3. What is the difference between Tungsten Halogen lamps and Metal Halide
lamps?
Tungsten Halogen lamps operate by the transfer of electrical current across a filament wire,
while a Metal Halide lamp (also called a Metal ARC lamp) operates by shooting the electrical
current across a gap in the wires.
4. Why should I avoid touching the lamp with my bare fingers?
Oil from the skin draws heat to the glass envelope of the lamp, creating a bubble that will result
in early failure.
5. Why doesn’t 3M use the same lamp type in all overhead projectors?
Overhead projectors are designed to satisfy different environments and applications. The best
lamp is chosen to fulfill the requirements of a particular overhead projector design.
6. Why effect does turning the overhead projector on and off during a
presentation have on lamp life?
Theoretically, turning a lamp on and off during its life cycle will slightly decrease its life. 3M
believes, however, that the benefit to a more effective presentation far outweighs any decrease in
the lamps life.
7. Why are some overhead projectors brighter than others, even thought the
same lamp type is used?
The other optical components also contribute to the amount of light that reaches the screen, such
as:
1. The number of glass (lens) surfaces the light must pass through.
2. The use of low-glare fresnel lenses.
3. Special optical features such as lens coatings, mirror surfaces, etc.
4. Normal variations in light output among brands and batches of lamps.
5. Collection of dust on the optical system.
8. Does a crack in the base of an ENX or FXL lamp mean the lamp is defective?
A crack often appears in the base of ENX and FXL lamps after a short time of use. This does not
affect the life or performance of the lamp.
9. How does the cooling fan affect lamp life?
The fan removes hot air from the lamp area to reduce the lamp’s seal temperature and protect
other machine components.
10. Does the “post-cool” or “let-run” fan feature in some overhead projectors
contribute to longer lamp life?
Continuing to run the fan after the projector is turned off does not contribute to longer lamp life.
If the overhead projector cooling system is properly designed, excessive heat will not remain in
the machine after it is turned off.
In overhead projectors with metal Halide lamps, the “let-run” feature maintains the proper
temperature of the lamp by ensuring that the fan will not run until the lamps heats to the correct
operating temperature, and then will continue to run once the unit is shut off until the lamp has
cooled sufficiently.
11. What is Lamp Life?
The average rated life of a lamp is the length of time when one half of the lamps in a large
sample have failed. For example: If 100 lamps, rated at 75 hours are all turned on at the same
time, 50 will have burned out before 75 hours and 50 will continue to burn after 75 hours.
Lamp life ratings are established by the lamp manufacturers and confirmed by controlled
laboratory testing. In addition, 3M conducts our own testing of the lamps we supply in our
overhead projectors.
Customer concerns regarding lamp life in overhead projectors fall into the following scenarios:
1. A customer purchases a new overhead projector and the lamp either doesn’t light initially
or it fails within one hour of use.
2. Customers with a large number of overhead projectors are not experiencing the life from
their lamps that they expect.
3. Customers experience variations in lamp life from one lamp to another or one overhead
projector to another.
Let’s discuss the lamp life issues in each of these scenarios:
Scenario #1: A Customer purchases a new overhead projector and the lamp either
doesn’t light initially or it fails within one hour of use.
All 3M overhead projectors are tested at the factory before being packaged. In spite of this,
some lamps fail initially when the projector is first used. We believe the shipping process or the
stress of initial use contribute to this problem.
If the lamp fails to light when a new overhead projector is unboxed and plugged, the user should
first check to be certain the lamp is seated completely in the lamp socket. If the fan runs and the
lamp still fails to light or lasts only a short time, the lamp is defective.
Scenario #2: Customers with a large number of overhead projectors are not
experiencing the lamp life that they expect.
If a customer has a large number of overhead projectors and is not satisfied with the overall life
of the lamps being used in them, we must first determine if the average lamp life meets the
manufacturer’s rating. Carefully monitoring the actual number of hours each overhead projector
is used is the only way to accurately determine the average life of each lamp in that customer’s
situation.
If it is determined that the lamps are achieving the manufacturer’s rated life, there are a couple of
alternative that can be employed to extend the lamp life even further. Each of these methods will
approximately double the life of the lamp, BUT with a reduction of approximately 20% in light
output.
1. A –5 lamp version can be used in place of the standard lamp. For example, an ENX-5
can be used in place of an ENX. Lamps used in current 3M overhead projectors that are
available in a –5 version are: ENX and EYB. They are available from various lamp
sources.
2. An overhead projector equipped with a resistor will offer longer life by reducing the
voltage to the lamp. Some 3M models are equipped with resistors at the factory or
resistor kits may be purchased and installed in some other models. The resistor will not
eliminate the problem of premature lamp failures.
If monitoring actual usage determines that overall lamp life is below the manufacturers rating,
the following factors should be considered.
Line Voltage – Lamp life ratings are based on the stated lamp voltage indicated on the lamp
packaging or the lamp itself. The overhead projector line voltage indicated on the serial
nameplate should match the lamp voltage, however line voltages are not always stable and may
fluctuate.
The following chart illustrates the effects of line voltage on lamp life for both 120 and 230 volts:
Effects on Life and Light Output 120 V
Line Voltage
Light Output
% Of Lamp Life
Rating
130 Volts
125 Volts
120 Volts
115 Volts
110 Volts
134%
116%
100%
86%
73%
35%
60%
100%
171%
298%
Line Voltage
Light Output
% Of Lamp Life
Rating
250 Volts
240 Volts
230 Volts
220 Volts
210 Volts
130%
115%
100%
85%
75%
35%
60%
100%
200%
350%
Effects on Life and Light Output 230 V
Example: An ENX lamp rated for 75 hours, if used in an OHP receiving 125 Volts from the wall
socket, will emit 16% more light but with a life of only 60% of its rated life (or 45 hours)
Shock – Lamp filaments are fragile when a lamp is on and will likely fail if the overhead
projector is moved or jarred while turned on. Some lamp changing mechanisms, if used roughly
will also shock lamps, causing them to fail.
Diode – The diode is the electrical component in certain overhead projector models that
effectively reduces the incoming line voltage to the lamp. If the diode fails, the lamp will
receive the full line voltage and fail immediately. If the lamp burns longer than five seconds, the
diode is OK.
Defective Lamps – There is considerable variability in lamp quality. Replacement lamps,
available from many sources at widely varying prices, may contain manufacturing defects,
seriously affecting the service life of the lamp.
If a large number of new overhead projectors are placed in service at the same time, most of the
lamps could fail around the same point in time causing it to seem as though the new overhead
projectors are using lamps excessively. After the overhead projectors have been used for some
time, the lamp replacement rate will spread out due to the natural variation of the overhead
projector usage.
Scenario #3 – Customers experience variations in lamp life from one lamp to
another or one overhead projector to another.
There is a wide manufacturing variation from lamp to lamp in actual usage. For example: In a
large batch of good quality lamps, rated at 75 hours, it would be normal for only half of the
lamps to last 75 hours. The following charts illustrate a normal skewed distribution of life from
a batch of 100 lamps, and different types of lamps and their average hours of life.
Failed
Lamps
100
90
80
70
60
50
40
30
20
10
0
x
x
x
x
25
x
35
45 55
65
75
85
95
Example: After 85 hours of use, 84 lamps out of the batch of 100 will have burned out.
3M cooperates closely with our lamp supplies to verify performance of the lamps we supply in
our overhead projectors. If you believe your lamp performance does not follow this distribution,
please refer back to Scenario #1:
Lamp
ENX
EPW
EVW
FXL
EHJ
EVD
FNT
EYB
FSX
FSY
Volts
82
100
82
82
24
36
24
82
230
240
Watts
360
360
250
410
250
400
275
360
400
400
Line V
120
100
120/127
120/127
230/240
230/240
230/240
120/127
230
240
Ave. Lamp Life
(in Hours)
75
75
60
50
50
50
75
75
50
50