Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

brightness vrs. power



Hello,

I have a question on bulbs in a DC-circuit. What is a relationship between power dissipated in a bulb and brightness? I have seen some conceptual exercises which seem to assume that brightness is directly proportional to the power dissipated. I found a definition for ”brightness”: it is called luminance. Luminance is connected to the luminous intensity which is directly proportional to radiant energy.

Radiant energy depends on temperature of a filament. For instance when two similar bulbs are connected in series the net current is (approximately) halved. The power dissipated in both bulbs is reduced by factor 1/4. But has brightness reduced by the same factor? The current decreases and hence the temperature decreases. Then intensity and position of the peak wavelength changes more or less like in case of black body radiation. This curve (intensity against wavelength) is *not* linear. Would this mean that brightness is not directly proportional to the power dissipated? Or is there a mistake in my reasoning?

Regards,

Antti Savinainen
Kuopio Lyseo High School
Finland