Does Combined Luminosity of LEDs Add Up?

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SUMMARY

The combined luminosity of two LEDs, such as a green and a red LED, each rated at 2 W, does not simply add up to 4 W due to directional emission characteristics. Luminosity is a measure of total output power, but the effective power received can vary based on the angle of emission relative to the observer. Therefore, if the LEDs are not oriented in the same direction, the perceived luminosity will differ, leading to a combined output that may not equal the sum of their individual ratings.

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Say you had a green and red LED, both with a luminosity of 2 W would the combined luminosity be 4 W or still 2 W?
Say you had a green and red LED, both with a luminosity of 2 W would the combined luminosity be 4 W or still 2 W?
 
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Euan12345 said:
Summary:: Say you had a green and red LED, both with a luminosity of 2 W would the combined luminosity be 4 W or still 2 W?

Say you had a green and red LED, both with a luminosity of 2 W would the combined luminosity be 4 W or still 2 W?

On the face of it, I would say 'yes', since luminosity is a measure of total output power. However, your sources aren't isotropic emitters: the radiance of these sources strongly depend on the angle with respect to each emitter's surface normal.

What that means is that if the sources are not facing the same direction, the received power from each source is likely different.
 

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