# How hot is a 40watt lightbulb?

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Ok, this may sound like a strange question but how hot does a 40watt bulb get on the glass part of the bulb. I am needing to know what the maximum temperature would be. Guesses are welcome too as I have no idea.

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impossible to determine without other factors being taken into consideration.

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do an experiment!

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I remember when I was young I tried this "experiment" I held an outdoor thermometer up to a bulb in a lamp and ended up with broken glass all over.

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It will be pretty hot if it is incandescent (I cant give number though) but if it Fluroescent bulb then may be just room temp..

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A big factor will be how long the light has been on for, it starts off at room temp!

Also stuff like is it enclosed in a box or in the open so heat can disperse quicker.

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and how far is the glass from the heating fillament and what gas is used inside, all these things are critical for a correct answer.

anyway, why not, as suggested, get a cooks thermometer and test this yourself?

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I held a digital thermometer up to a 40w reflector lamp once and it went above 150 degrees C before i got bored lol.

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- use a thermocouple prob (K TYPE) connected to a digital multimeter.

- rotate the multimter selector to "temp" position.( you can select either °F or °C )

- put the prob on the bulb and see the display of multimeter rising progressively.

- you can draw a "temperature to time" curve.

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Ok, this may sound like a strange question but how hot does a 40watt bulb get on the glass part of the bulb. I am needing to know what the maximum temperature would be. Guesses are welcome too as I have no idea.

Here is the equation for radiative heat transfer. Temperature must be in K, and you need the area of the bulb. You'll get the temperature assuming no conduction or convection, which is the max theoretical value.

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