Why is it necessary to use absolute photometry for LEDs?


The lumen output of a LED is dependent on the thermal management / heat sink design, the electrical characteristics such as the junction and rated ambient temperature, the driver currents, and the optical system. This means that the light output is very much dependent on the design of the actual luminaire. This is unlike other light sources like HID where the photometrics of a luminaire are fairly independent of the lamp used.