You have undoubtedly noticed that the sun appears yellow rather than bright red. The kind of light detectable by the human eye is called visible light, which has a wavelength between around 400 to 700 nanometers. The human eye is said to be most sensitive to light in wavelengths around 500 nanometers.

It is believed that the reason behind this sensitivity is the evolution of the human eye by adaptation to the solar spectrum. If the sun were a much hotter star, the range of visible light would have been different. However, the environment on present-day earth would likely be far different, and it is doubtful that human beings and other organisms would ever come into being.