Measuring Etendue of LED sources

[Samu]

How does one measure the etendue experimentally (when the area of the emitter and the angular distribution is not provided) in order to compare the focusing strength of two LED sources in an optical setup?

Thanks!

 

[UltrafastPED]

Here is a lab exercise: http://engineering.tufts.edu/bme/people/georgakoudi/EN31Lab5PolarizationLab.pdf