Calculating correlated color temperature with a desktop programmable calculator

The chromaticities of Planckian radiators in an x, y diagram can be approximated with two polynomials coupling x to the inverse temperature and y to x. The correlated color temperature (cct) of a source can be calculated by using these (xP, yP) values and a simple algorithm to find that particular (xP, yP) point that lies nearest to the chromaticity coordinates of the light source, for which the cct is computed. The temperature used in computing the (xP, yP) point with minimum distance from (x1, y1) is the cct of the source. Another simple algorithm can be used to generate the lines with constant cct for any temperature of a Planckian radiator, in the region 2000–50,000 K. Calculations using these algorithms can be performed using small desktop calculators. The computations can be automated if the memory capacity is equal to 20 registers and the program can be written in the length of 200–400 program steps, depending on the program handling possibilities of the calculator.