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# how to measure the brightness of a bulb watch

1. I have been given a brilliant club final assignment on light sources and I have been asked how to measure the brightness of different light sources (LEDs, incandescent lights, CFLs etc) using steradians, luminance and flux which I am unsure about as I have only just finished my AS exams.
Would appreciate any help and insight on my problem
2. (Original post by tika8)
I have been given a brilliant club final assignment on light sources and I have been asked how to measure the brightness of different light sources (LEDs, incandescent lights, CFLs etc) using steradians, luminance and flux which I am unsure about as I have only just finished my AS exams.
Would appreciate any help and insight on my problem
Understand the definitions of Steradian and luminance. Hint, it relates the surface area on a portion of a sphere, to the radius squared of that sphere.

i.e. A = r2

Luminance is a reference measurement (based on 1 lumen being approximately equal to 1 candle power).

So you need to relate Steradians to Lumens by calibrating your measuring equipment against the light output of a standard candle at a given distance from the candle.

The transducer used (possibly a LDR or photocell) will have an active surface area and this must be used in the Steradian calculation using the candle as a reference.

Once calibrated, and you have defined the rule for measuring and calculating other light sources using your apparatus, you are free to conduct your measurements.

Don't forget to think about sources of error and how to eliminate or minimise them. Think about external light sources affecting measurements, stray light from the source, the spread of wavelengths output from both the candle and the different light sources and also the detectable wavelengths for the light sensor. Then make a reasoned estimation for the accuracy and error of your measurements.
3. (Original post by uberteknik)
Understand the definitions of Steradian and luminance. Hint, it relates the surface area on a portion of a sphere, to the radius squared of that sphere.

i.e. A = r2

Luminance is a reference measurement (based on 1 lumen being approximately equal to 1 candle power).

So you need to relate Steradians to Lumens by calibrating your measuring equipment against the light output of a standard candle at a given distance from the candle.

The transducer used (possibly a LDR or photocell) will have an active surface area and this must be used in the Steradian calculation using the candle as a reference.

Once calibrated, and you have defined the rule for measuring and calculating other light sources using your apparatus, you are free to conduct your measurements.

Don't forget to think about sources of error and how to eliminate or minimise them. Think about external light sources affecting measurements, stray light from the source, the spread of wavelengths output from both the candle and the different light sources and also the detectable wavelengths for the light sensor. Then make a reasoned estimation for the accuracy and error of your measurements.
Thank you friend, that is most helpful appreciate the response

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