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Light Fixture - Input Current

Nick Parker

Say, if the rating of a light fixture is 36W, what does it refer to? Is it the output watts equivalent of lumens? or the input power required by the fixture? 

I ask this to calculate the input current to the fixture.

Input current = Watts / (Voltage x PF x Efficiency)

or

Input current = Watts / (Voltage x PF)

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    Traditionally it is the input power. light out is equal to this minus the losses that come out as heat instead, which in some designs can be most of the input !  

    The conversion between lumens of light into watts of light is a colour dependent  thing, as for the eye brightness response is not spectrally flat - most of us peak in the green at about 500 -700 lumens per watt, and tail off to less than  half this in the blue and the reds, and of course we see next to nothing in the UV and IR.

    Traditional filament lamps have a black body response, and generate about 100 lumens per watt, as most of the radiant energy is in the IR not the visible. LEDs can do much better, running quite cool, 

    Filaments have a nice resistive construction, electronic drivers for LEDs tend to have an awful power factor.

    Mike.

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  • 0

    Traditionally it is the input power. light out is equal to this minus the losses that come out as heat instead, which in some designs can be most of the input !  

    The conversion between lumens of light into watts of light is a colour dependent  thing, as for the eye brightness response is not spectrally flat - most of us peak in the green at about 500 -700 lumens per watt, and tail off to less than  half this in the blue and the reds, and of course we see next to nothing in the UV and IR.

    Traditional filament lamps have a black body response, and generate about 100 lumens per watt, as most of the radiant energy is in the IR not the visible. LEDs can do much better, running quite cool, 

    Filaments have a nice resistive construction, electronic drivers for LEDs tend to have an awful power factor.

    Mike.

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