Author Topic: Why and how do fluorescent tubes get warm?  (Read 2256 times)
F96T12 DD VHO
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Why and how do fluorescent tubes get warm? « on: February 05, 2018, 10:52:55 AM » Author: F96T12 DD VHO
Every time I turn on my F96T12 the tube runs at about 99-115 deg F and when I turn on a CFL it gets to 220 ish
Why do fluorescent lights get warm and why does it happen
This has been getting on my nerves ever since I got my first fluorescent light F15T8
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RyanF40T12
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Re: Why and how do fluorescent tubes get warm? « Reply #1 on: February 05, 2018, 04:34:32 PM » Author: RyanF40T12
The filaments are going to be warm/hot, that is part of how they work and emit what they emit.  Add to that you get heat radiating from the ballast as well. 
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Ash
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Re: Why and how do fluorescent tubes get warm? « Reply #2 on: February 05, 2018, 05:59:53 PM » Author: Ash
Every conductor bar superconductors have electrical resistance. Current^2 * resistance = warm
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Medved
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Re: Why and how do fluorescent tubes get warm? « Reply #3 on: February 06, 2018, 04:12:14 PM » Author: Medved
The main heat source are not that much the electrodes (there is just about 15..20% of the input power), but first the phosphor losses (the phosphor accepts energetic UV photon, emits way less energetic visible photon, the rest of excitation energy is then dissipated as an IR and/or direct heat). Other heat source is the direct UV absorbtion in the tube glass (the phosphor thickness is a compromise between UV utilization vs visible light absorbtion, so quite some part of UV passes through), the last part is the arc licking the tube, in other words accelerated charge particles collide with the wall material just generating heat as the result.

With 75lm/W efficacy you have roughly 25% energy efficiency in converting the electrical power into the visible light radiated power, the rest are losses. Some of them are in the form of the IR radiation, but majority is just a plain heat. With e.g. 25W spiral that means at least 15W just warming the glass and to be dissipated just by convection. When crammed in such way as the CFLs use to be, there is no other way to dissipate that power than via rather high surface temperatue...
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