The sun emits light at different wavelengths, which span across the visible spectrum and beyond, into ultraviolet and infrared. Interestingly, the peak of this broad spectrum of sunlight occurs in the yellow-green region, around 550 nanometers. This might suggest that sunlight should appear green to human eyes, but it doesn’t; instead, sunlight appears as white light. The reason for this lies in the way humans perceive color.
Visible light from the sun comprises a range of colors, each with different wavelengths - from the shorter wavelengths of blue and violet to the longer wavelengths of red. The yellow-green light, despite being emitted more intensively, is just one part of this diverse spectrum. When all these colors are combined, they add up to white light. This phenomenon is a result of the nature of "additive color mixing," where different light colors mix to form other colors, including white.
Human eyes also play a crucial role in why we perceive sunlight as white. The human eye contains three types of color receptors, or cones, sensitive to red, green, and blue light. These cones work together to interpret the various wavelengths of light as different colors. When the light from the sun enters the eye, the high intensity of yellow-green light stimulates these cones almost equally along with the other colors of the spectrum. Due to this equal stimulation, the brain perceives the combination as white, rather than any individual color dominating.
Moreover, the Earth’s atmosphere affects the coloring of sunlight. Particles and gases in the atmosphere scatter sunlight, especially at shorter wavelengths. This scattering, called Rayleigh scattering, is why the sky appears blue during the day as blue light is scattered all around. During sunrise and sunset, the light has to pass through more of the Earth's atmosphere, which scatters shorter wavelength light even more and allows longer wavelengths like reds and oranges to be more visible, giving rise to the rich colors typical of these times.
Thus, despite the sun emitting more green light, the comprehensive mix of all visible wavelengths and the effects of our atmosphere work together to ensure that we usually see this light as white. This illuminating interplay between solar emissions, atmospheric effects, and human vision showcases the complexities of color perception and environmental interaction.
