# Measuring LED's Chromaticity

To represent and calculate an accurate color by mixing LEDs, you need to know LEDs' chromaticity and brightness.
But most of LEDs do not come with such data.
You must measure them by yourself.
[Chromaticity meters](https://www.google.com/search?q=chromaticity+meter) are used for this purpose, but these are expensive and not for hobbies.
Here I describe a Maker's choice - use [SparkFun Triad Spectroscopy Sensor](https://github.com/sparkfun/Qwiic_Spectral_Sensor_AS7265x).

![AS7265x](https://camo.githubusercontent.com/05a63740a5d214c59d7073c0e3eb3d1b1c7ba898fc21da6c6f6342b42de03639/68747470733a2f2f63646e2e737061726b66756e2e636f6d2f2f6173736574732f70617274732f312f332f332f392f332f31353035302d537061726b46756e5f54726961645f5370656374726f73636f70795f53656e736f725f2d5f415337323635785f5f51776969635f2d30312e6a7067 "AS7265x")

## About AS7265x

[AS7265x](https://github.com/sparkfun/Qwiic_Spectral_Sensor_AS7265x) has 3 sensors to obtain 18 band spectroscopy from 372nm (UV) to 966nm (IR).
By denoting intensity of <i>i</i> th band output as <i>&alpha;<sub>i</sub></i>, we get the composite color [ <i>x, y, Y</i> ] as

[ <i>x, y, Y</i> ] = <i>&Sigma; &alpha;<sub>i</sub> [ x<sub>i</sub>, y<sub>i</sub>, Y<sub>i</sub> ]</i>