Heating effects of different lightbulbs

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Discussion Overview

The discussion revolves around the heating effects of different types of light bulbs, specifically comparing LED and halogen bulbs with the same power output. Participants explore how the differing radiation spectra of these bulbs might affect the temperature of the air and walls in a sealed environment over time.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that both bulbs will eventually reach the same equilibrium temperature, although the rate at which they do so may differ.
  • Others question the assumption that both bulbs consume and radiate the same power, noting that their radiation spectra differ, particularly in infrared output.
  • A participant clarifies that a bulb rated at a certain wattage emits energy in both visible light and heat, leading to a discussion about energy conservation and the relationship between input power and emitted energy.
  • One participant suggests that if the input power is the same, the behavior of both bulbs in the sealed environment would be similar, but acknowledges potential minor differences in temperature gradients due to the nature of heat transfer from each bulb.
  • Another participant raises a concern that the LED lamp may overheat and fail before the halogen lamp reaches its maximum operating temperature.

Areas of Agreement / Disagreement

Participants express differing views on whether both bulbs will behave identically in terms of heating effects, with some agreeing on the concept of equilibrium temperature while others challenge the assumptions regarding power consumption and radiation characteristics.

Contextual Notes

The discussion includes assumptions about the definitions of power and energy output, as well as the implications of different radiation spectra on heating behavior, which remain unresolved.

Who May Find This Useful

Individuals interested in the thermal properties of lighting technologies, energy conservation principles, and the comparative analysis of LED versus halogen bulbs may find this discussion relevant.

f todd baker
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Suppose I have two light bulbs, an LED and a halogen, but both have the same power P. Their radiation spectra are different, the LED radiating much less IR. Putting them in identical closets from which no heat may escape, will the walls and air in each come to some temperature T which, although increasing, will be the same for both?
 
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f todd baker said:
Suppose I have two light bulbs, an LED and a halogen, but both have the same power P. Their radiation spectra are different, the LED radiating much less IR. Putting them in identical closets from which no heat may escape, will the walls and air in each come to some temperature T which, although increasing, will be the same for both?

What do you think?

First can I check what you mean by "power P" ?

Is it..

a) The same power going into each light?
b) The same amount of visible light emitted by each light?
 
both consume and radiate the same power
what do I think? I think that there would be a time when both were at the same temperature ("equilibrium" between walls and air) and that temperature would be increasing. I think it possible that one would reach that equilibrium more quickly than the other.
 
f todd baker said:
both consume and radiate the same power

That can't be true (in the visible, the question you were asked) given your previous statement.

f todd baker said:
Their radiation spectra are different, the LED radiating much less IR.
 
I do not understand that. A bulb which is rated at 13 W, e.g. means that perhaps 8 W is radiated as visible light, 5 W as heat (IR). Whatever, whatever the bulb consumes must equal the energy radiated or else energy will be being stored somehow in the bulb.
 
F Todd: You are correct. Conservation of energy means all bulbs consume as much as they emit overall. That's why in b) I asked if you meant equal _visible_ output. (A 500 lumen halogen consumes more power than a 500 Lumen LED).

If the input power is the same then I would expect both boxes to behave more or less identically. However there might be minor differences. For example a halogen will be hotter than an LED so more of the power will leave the bulb by conduction/convection rather than radiation - so the temperature gradient between bulb and outside will be different (I think).
 
Last edited:
Sadly, the experiment will not run for very long as the LED lamp will overheat and fail long before the halogen lamp maxes out...
 

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