halogen lamp & LCD display

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xxTurbonium

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Oct 8, 2006
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Is it true that direct sunlight damages LCD displays? If so, I am assuming this has something to do with the UV light which, over time, breaks apart the crystal compounds used in the display.

Using the same logic, wouldn't it also be fair to assume that a halogen desk lamp poses the same risk to an LCD display? Even assuming you use a glass UV filter, since I doubt they filter out 100% of all the UV light...

Side question: is the effective output of UV light, per unit area, higher from the Sun, or from a halogen lamp only centimeters away from a given object? (obviously the Sun is orders of magnitude greater in total output, but I mean per unit area, since the Sun is also orders of magnitude farther away from a given object than is a desk lamp). In case it matters, say a 50W halogen lamp. Could you just argue that the Sun, still being brighter per unit area than the lamp bulb, also emits more UV light per unit area? (i.e. I won't be able to tell if the lamp is even on if I turn it on outside on a sunny day).
 

Rubycon

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UV emission, post filter, on halogen bulbs is minuscule in comparison to sunlight in any latitude.
 

xxTurbonium

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Got any papers I can read concerning UV emissions from halogen bulbs in general? I'm curious.

I'd be curious to read something along these lines as well. :)
 

AstroGuardian

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the amount of UV light that comes from the sun is greatly dependent of the thickness of the atmosphere and its constitution. So how would you measure it? One crucial parameter is always messing things up right?
 

Turbonium

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Originally posted by: AstroGuardian
the amount of UV light that comes from the sun is greatly dependent of the thickness of the atmosphere and its constitution. So how would you measure it? One crucial parameter is always messing things up right?
You're missing the point. I was just looking for an average value, which is relatively trivial to obtain for both pre- and post-atmosphere.
 

Paperdoc

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Aug 17, 2006
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The Wikipedia article on "Halogen Lamp" includes this paragraph under "Safety":

Additionally, it is possible to get a sunburn from excess exposure to the UV emitted by an undoped quartz halogen lamp. To reduce unintentional UV exposure, and to contain hot bulb fragments in the event of explosive bulb failure, general-purpose lamps usually have a UV-absorbing glass filter over or around the bulb. Alternatively, lamp bulbs may be doped or coated to filter out the UV radiation. When this is done correctly, a halogen lamp with UV inhibitors will produce less UV than its standard incandescent counterpart.

Note the last sentence. While it gives no numbers, it does indicate that a properly-filtered lamp puts out very low UV.

How does the UV affect LCD displays? OP speculates it is by degrading the liquid crystal chemicals, and that's reasonable, though I cannot confirm or dispute that. I do know that most polymers (such as the plastics used in screens) can be damaged by UV light, leading both to discoloration and darkening and to physical loss of strength / brittleness.
 
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