White point estimation of an RGBC color sensor to measure dominant wavelength

Abstract

This paper proposes a methodology to calibrate an RGBC sensor to measure the dominant wavelength of visible light sources. For this, it is proposed to use the TCS34725 sensor capable of blocking the infrared components and providing an intensity signal, to obtain an invariant measurement of ambient radiation and the intensity of the source. The method consists of: (i) normalization of the Red (R), Green (G), and Blue (B) components between 0 and 255, using the Clear Light (C) signal; (ii) representation in the CIE 1931 color model; (iii) transformation to CIE values xyY and (iv) estimation of the dominant wavelength with the use of the chromatic diagram. The experiment was carried out using data acquisition system based on an atmega328p-pu microcontroller which communicates by the I2C protocol with the RGBC sensor equipped with its analog-digital converter. To reduce errors, the system was calibrated using a white light source and three optical filters (578nm, 546nm, and 405nm) to obtain three quasi-monochromatic sources and obtain the white point of the sensor. With this methodology, measurements located within the bandwidth of the source and with errors of the dominant wavelength between 0.01 % and 6.6 % were achieved.