DIY LEDs brightness tester.

To reach an homogeneous output an accurate calibration is needed. Same LEDs can have different brightness so is important to find if there are LEDs brighter than others and substitute them. LEDs brightness is usually measured with a spectro-radiometer and an integrating sphere this allows very accurate, absolute and quantitative measurements. In our case we don't care about an absolute value in $W/m^{2}$ or in LUX we simply want to know if a LED is brighter than another. This seems a easy task to perform with a simple camera: measuring pixels values, but in fact it isn't because in a breadboard (when you usually make the prototype of your lamp) little variation of the LED inclination cause huge differences in light output. One possible solution is to use another LEDs as a photodiode and measure the voltage or the amps generated by the source LED. This instrument is quite easy to build, I've used a plastic wine's bottle cap to imbed securely the "probe LED". The "probe LED" is inserted in a narrower side of the parallelepiped, a larger diameter in the other side allows an easy removing of the LED from the probe, when the source LED is inserted in the other side.

Simple LED brightness tester Leds 3d models by LED signal light user

It is simpler to design the probe so that the source LED touches the probe LED when you are measuring. In this way you are sure that the distance is every time the same. We will see in the next post how to collect the data of many LEDs effectively.