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starry night
12-05-2011, 10:31 PM
I was just reading an old article on Mike Gambino's site. He mentioned that as part of maintenance he replaces halogen bulbs every two years even though they are not burned out. He said they become dimmer as they age.
Can someone explain the technical reason for them becoming less bright.

steveparrott
12-06-2011, 09:55 AM
I was just reading an old article on Mike Gambino's site. He mentioned that as part of maintenance he replaces halogen bulbs every two years even though they are not burned out. He said they become dimmer as they age.
Can someone explain the technical reason for them becoming less bright.

In halogen lamps, if the glass or quartz envelop remains clear and the reflector does not degrade then you would expect at most, about a 5% decrease in lumen output (lamp lumen depreciation - LLD) over the life of the lamp. The 5% loss primarily caused by slight degradation of the filament.

Halogen lamps with reflectors (e.g. MR16 and PAR38), however, are subject to much more dramatic losses - losing huge amounts if the reflector is poorly designed and degrades significantly.

Other causes of LLD include deposition of tungsten on the inside of bulb envelope (black coating) - often cause by under-voltage operation; or a white coating that can be caused by a bulb not properly sealed (or cracked) allowing intrusion of moisture and contaminants.

Inexpensive lamps are prone to LLD for the above (and other) reasons.

If you use high quality halogen lamps and operate them at the right voltage, there should be no concern about LLD.

It may be a good idea, however, to replace all lamps in a system every 18 months to 2 years to simplify maintenance. It helps ensure that all lamps will be operating at all times, rather than homeowners or contractors having to chase down single burnouts throughout the year.

starry night
12-06-2011, 02:33 PM
Thanks for the lucid (:)) expalnation, Steve. I have learned a new term LLD.
I was going to use the term "degradation" in my question but didn't want to be wrong in terminology. Turns out I was close.

steveparrott
12-06-2011, 02:59 PM
Thanks for the lucid (:)) expalnation, Steve. I have learned a new term LLD.
I was going to use the term "degradation" in my question but didn't want to be wrong in terminology. Turns out I was close.

'Degradation' usually refers to a worsening condition - 'clouding, 'corrosion', 'oxidation', and so on.

'Depreciation' refers to a lessening value that can be caused by component degradation.

Another oft used related photometric term is Light Loss Factor (LLF). This is the ratio of the initial exiting lumens divided by the average exiting lumens (over the lamps lifetime). This is an extremely important value for lighting designers who need to ensure a certain illuminance over a number of years.

starry night
12-06-2011, 06:13 PM
Sort of like in West Side Story: I got depreciation on accounta I got degradation.

S&MLL
12-06-2011, 06:13 PM
We run our mr16s hotter then most (11.8-12.2) I like the color better as do most of my clients. With that said we replace all lamps every spring. Might be costly but it allows my clients to not worry about bad lamps. Also when we do our fall service we replace all 921s or 918s. They cost maybe a buck a price and this is great for us since the lamps last till the next spring service call.





This works for us. Might not work for every company in every region. I also do not like service calls for bad lamps when it is 15* outside and snow on the ground. Plus we go into snow mode and don't carry anything lighting related on the trucks from about now till march.


When doing the maintenance this way we may get 1-5 mid year service calls. Most are storm or mower damage. Very very rare to get a bad lamp call say in June.



To wrap this up. When it comes to service.... Charge what is fair for what you do. I have never had a client complain about our cost. And once I explain why we change lamps that are still fine they understand
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