Why is yellow the lightest color of the spectrum?
The short answer is, it’s not. Your question could be interpreted many ways. That answer is technically correct, but there are other ways to look at it. If you just took spectral lights and looked at them one wavelength (essentially hue) at a time and had equal amounts of each, then the brightest would be a green wavelength around 555nm. If you look at objects like artists paints, then a saturated yellow color often looks lighter than a saturated green (or other hue). This has several reasons. Mainly is that the yellow will be reflecting more light than the green (often green, yellow and red light to produce a yellow). However, whether or not it looks lighter will depend on the particular pigments being used and the lighting conditions. It might also depend on the observer. For further study, I would recommend a book on color order systems. You might look at some of the books on the Munsell System, or a book like “Color Space and Its Divisions” by Keuhni for a more detailed treatment.
