Quantitative Measurements of RGB and CMYK Colours with a Homemade Spectrophotometer

We show how students can use smartphones photo cameras to inspect the nature of colours and favour understanding of the different physical mechanisms governing the perceived colours. For this purpose, students studied the spectra of RGB colours emitted from an LCD screen and the transmission spectra of CMY pigments of a laser printer after analysing the colour sources also from a microscopic point of view. To this aim, students first used a rudimental microscope, putting a drop of water on the cell phone camera, then assembled a low cost spectroscope, based on the use of inexpensive diffraction transmission gratings. Students employed their hand made spectroscopes to obtain quantitative spectra of the colours emitted from the LCD screen and the transmission spectra of coloured lines stamped by a laser printer. The sequence of activities is aimed at undergraduate students and has been proposed for preliminary testing to twenty undergraduate students in order to study the feasibility and educational potential.