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       The energy liberated by sun reaches the surface of earth in the form of three types of waves, all having different wavelengths. These are:

  1. Ultraviolet rays
  2. Visible light and
  3. Infra-red rays

       Out of these three types of waves, the ultraviolet rays and infra-red rays are invisible, i.e. these cannot be seen with naked eyes. Thus, the only part of sun’s energy which can be seen is visible light.

Solar Spectrum

Visible light

       The wavelength of visible light lies between 400 nm to 770 nm. The visible light consists of seven colours namely violet, indigo, blue, green, yellow, orange and red. The wavelength of violet light is 400 nm and that of red is 770 nm. The remaining five colours have wavelengths between violet and red colour.

Ultra violet light

       The wavelength of ultra violet rays is shorter than violet light, i.e. wavelength of ultra violet rays is less than 400 nm. The ultraviolet rays are very harmful to us and cause many harmful health problems when fall on the body for a long time. For example, when a person is exposed to ultraviolet rays for a long time, then these rays can change colour of his skin or may cause skin cancer. Usually, the ultraviolet rays present in sunlight cannot reach the surface of earth, as most of ultraviolet rays are absorbed by ozone layer present in the upper atmosphere of earth. Thus, we are protected from the harmful effects of ultraviolet rays by a natural protective cover called ozone layer which is present in the upper atmosphere of earth.

Infra red rays

       The wavelength of infra-red rays is more than red light, i.e. the wavelength of infra-red rays is more than 770 nm. About 33% part of sun’s energy consists of infra-red rays. Infra-red rays cannot be seen, but we can feel it as heat. For example, we feel sunlight hot due to the presence of infra-red rays in it. It should be noted that all the objects also start emitting infra-red rays when they get heated. For example, when an electric iron or electric water is heated by supplying electricity, it starts emitting heat energy in the form of infra-red rays.

Test Your Understanding and Answer These Questions:

  1. What is solar spectrum?

  2. What is wavelength of visible light?

  3. What is wavelength of ultra violet light?

  4. What is wavelength of infra red rays?