Sunday, August 29, 2010

The LED's Luminous Emittance

The LED's emissions are not the same in all directions. To capture this I placed a frosted glass plate in front of the LED at various distances from it and took a picture of the illuminated plate. As the pattern gets larger farther away from the LED one can make out the shape of the luminous square inside the LED.

3 cm

9 cm

15 cm

There seems to be a "halo" which surrounds the brighter center of the pattern and grows linearly with distance.

The edge of the halo marks a cone which bounds the emitted light. The angle between the lines common to a plane cutting the light cone in half and the light cone is 18°. At larger distances the central pad where the whisker makes contact interferes with a uniform distribution of light.

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