Wavelengths and colors

That part of the Electro Magnetic Spectrum that human eye can see is termed as Visible Spectrum or Visible light or simply Light. And this consists of wavelengths from 400 – 700 nm. Many animals and insects have eyes that are sensitive to other wavelengths outside of the human visible spectrum. Bees and other insects use ultraviolet radiation to find nectar, Some species of birds has sex dependent markings on their plumage only visible in ultraviolet light; proof of their eyes sensitivity to ultraviolet frequencies.

Light Wave - Courtesy Wikipedia

But for all purposes we are only concerned about what the human eye could see. Human eye has three kinds of light receptors; they are blue, green and red. We perceive color depending upon the strength of each type of waves. For example if the light we see has more red waves we see light as red. And when all three light receptors are stimulated equally we see white or neutral grey. An understanding of the sequence of colors of the visible spectrum will help you choose color filters for a scene and also understand the response of the film and digital sensors to various colors.

Wavelength of Visible Light

Human eye could only see wavelengths from 400 – 700nm.

When all wavelengths are present in a light emission the result appears white and colorless.

When only some of the wavelengths are present in a light it appears colored.

What we perceive as cooler colors (blue) has the shortest wavelength and what we perceive as hot colors (red) has the longest.

When light passes through atmosphere short wavelengths are easily scattered and that is the reason why midday sky appears blue.

During sunrise and sunset the sunrays travels more distance through the earth’s atmosphere as it is coming at an angle. And during the process

short wavelengths get filtered out and only the longest wavelengths reach earth’s surface. That is the reason for the yellow light during sunrise and sunsets.

White light has all the frequencies in the visible region and has all colors blue, green, yellow, red etc present. Depending upon the change in wavelength the color of light changes.

At 400 – 450 nm we see light as dark purple - violet.

At 450 – 500 nm the light appears blue.

At 500 – 580 nm light appears more blue – green.

At 580 – 600 nm we see yellow.

At wavelengths longer than 600 nm the color of light changes to orange.

At 650 nm light looks red

And at 700 nm it appears to be a darker shade of red.

In the next article we will discuss how light behaves when it falls on a surface.