# Thread: temp from light lumiance

1. Hi,

Is it possible to calculate the temperature from light lumiance?

There are some hard tasks in this like temperature may b low even though light lumiance is more (due to ac) or in some cases temperature may be more than light lumiance.

Is there a generalized and perfect way to find temp from light lumiance?

(I only have light lumiance and no more device. I want to calculate temp from light lumiance only)

2.

3. Can you clarify?
If you set a thermometer under the light... the reading will indicate how much the light heated it at that distance and so on.

4. No. I only have light lumiance and no more device. can we calculate temp from it?

5. Do you mean luminance?
I don't know how you can measure it without a measurement device.

6. I can find lumiance from android sensors. temp calculating devices can only find temp of battery and not surroundings. Light sensor can sense lumiance. I want to get the actual temp of surrounding from light lumiance.

7. Originally Posted by saurabhshelar
I can find lumiance from android sensors. temp calculating devices can only find temp of battery and not surroundings. Light sensor can sense lumiance. I want to get the actual temp of surrounding from light lumiance.
Ok, so you do mean luminance.

You're thinking that one form of energy: EM radiation- would exhibit the same properties as another form of energy: Heat.
You want the temperature of light itself.
The EM radiation strikes mass and some of the energy is transformed into heat.

8. is there any method of calculation to get the temp out of it?

9. Originally Posted by saurabhshelar
is there any method of calculation to get the temp out of it?
You are assuming that EM radiation has a temperature of its own because when EM Radiation strikes mass, some of the energy is transformed into heat.
Light can have a temperature in certain situations:
Black-body radiation - Wikipedia, the free encyclopedia
A good example of this is the CMB- Cosmic Microwave Background that we observe as a remnant of the Big Bang event.

Most of the time, emitted light has a spectrum that is different from the equilibrium "blackbody" spectrum. You cannot say that light "has a temperature" in this instance.

10. ahaaa....okkk....so it means that my assumptions to calculate temp from light lumiance is not perfect.

11. Originally Posted by saurabhshelar
ahaaa....okkk....so it means that my assumptions to calculate temp from light lumiance is not perfect.
Not perfect, yes, but not totally off base, either. More importantly, your question is an excellent question and I regret not being knowledgeable enough about it to really help you.
I gave the example of the CBR (Cosmic Background Radiation) above, which demonstrates how important the question is.

12. ya surely...right nw m reading them and thanks for info.

13. Originally Posted by saurabhshelar
ya surely...right nw m reading them and thanks for info.
Saurabhshelar, you cannot determine temperature merely from the amount of light emitted, i.e. luminance.

You need also to know the spectrum of the emitted light, i.e. how much light is emitted at different frequencies. And doing even this requires knowledge of how the emitter of the light is working. For example an incandescent filament will radiate like a "black body" and its temperature can be measured using a pyrometer. However a sodium street lamp emits by excitation of the emission spectrum of sodium vapour. The concept of temperature does not really apply to this type of emitter, since its emission is not due simply to heating it.