One theory of color vision is based on the existence of different types of cones for the detection of short, medium, and long wavelengths. What is this theory

The theory of color vision which is based on the existence of different types of cones for the detection of short, medium, and long wavelengths is called Trichromatic Theory.

Tri stands for three and chroma is the Greek word for color. The term 'trichromacy' (also called trichromatism) refers to the condition of having three independent channels that convey information about colors, derived from three different types of cones. The three types of cone cells have different absorption spectra. These three receptors react to light of three different wavelengths - red, green and blue. These cells are responsible for the perception of colors.

Evidence for the trichromatic theory comes from color matching and color mixing studies. Young and Helmholtz carried out experiments in which individuals adjusted the relative intensity of 1,2, or 3 light sources of different wavelengths so that the resulting mixture field matched an adjacent test field composed of a single wavelength. Individuals with normal color vision needed three different wavelengths (i. e., primaries) to match any other wavelength in the visible spectrum. This finding led to the hypothesis that normal color vision is based on the activity of three types of receptors, each with a different peak sensitivity. Consistent with the trichromatic theory, we now know that the overall balance of activity in S (short wavelength), M (medium wavelength), and L (long wavelength) cones determines our perception of colour.