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I read some where that there are three types of UV and infrared rays namely UV-A, UV-B, UV-C and near infrared, mid infrared and far infrared. Which is the most abundant among the the three in Ultraviolet and infrared radiation from sun? I mean there is a total of 1000 W per unit area illumination by sun among which more than 500 watts is infrared, around 450 watts in visible and the rest part is ultraviolet so in the infrared rays which are the most abundant means which contribute to most of the 500 watts? Also, what are the sources of infrared at night and what is the power density of infrared rays at night!.

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Hi Saurbh. Welcome to Physics.SE. Can you provide a reference on the power distribution? –  Waffle's Crazy Peanut Apr 22 '13 at 18:01
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Wikipedia has a good plot of the power versus frequency spectrum, well labeled.

solar radiation

One can integrate numerically to get the percentage at each wavelength. There exists also an article on ultraviolet.

Please also tell what are the sources of infrared at night and what the power density of infrared rays at night!.

Infrared at night comes from the stored sun energy on matter, ground and air. It follows the black body radiation spectrum, which is directly dependent on the temperature, which falls as energy is radiated away. This is a small number in watts/m^2 and can be calculated using the Stephan Boltzman law.

black body

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Just to add to this answer: you can see from the first plot that the sun's output is peaked around visible light. Therefore UV-A has a higher intensity than UV-B and UV-C sice it has a longer wavelength; and similarly near infrared has a higher intensity than mid and far infrared. To calculate how much power per unit area is in the form of UV-A (for example), you would need to find the area under this curve from 315 to 400 nm. –  Nathaniel Jun 22 '13 at 15:31
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