UV Light

What Is UV Light?

UV light (ultraviolet light) is having a wavelength between 10 to 400nm that are shorter than the visible light but longer than the X-rays and is a type of a electromagnetic radiation. These are present in sunlight and contributes 10% of the total light from the sun.

UV Light

Types of UV light

UV light or UV ray is classified into three components ultraviolet A (UVA), ultraviolet B (UVB) and ultraviolet C (UVC). Following is the table explaining the characteristics of these components:

  • Ultraviolet A (UVA):
    • Most of the UV (98.7%) that reaches us on the earth’s surface is of type UVA and is affected by the ozone.
    • It can be the cause of aging of the skin.
    • Fading of paints and dyes.
    • It is the cause of skin cancer called melanoma.
  • Ultraviolet B (UVB):
    • 1.3% of the UV reaches the earth’s surface and is highly affected by ozone.
    • These rays are responsible for sunburn and tan.
    • For the production of Vitamin D, 270-300 nm wavelengths are stimulated.
  • Ultraviolet C (UVC):
    • 0% of the rays reach the earth’s surface as most of them are scattered and absorbed by the atmospheric oxygen, nitrogen and ozone.
    • Causes lesions on the skin.

To understand UV light below is the experiment explaining how UV protection is obtained using sunglasses.

How Does Sunglasses Work?


The main objective of this science model is to know about the protection which is offered by sunglasses and sunscreens to the ultraviolet light. The experiment helps you in understanding how to block the ultraviolet light. The experiments here are compared and quantified to the effectiveness of the sunscreens with various strengths, ages, brands under a different set of conditions.


Ultraviolet light sensitive disks are the ones that are used in testing the amount of light able to make way through the sunscreen or some protective surface. When these disks absorb the ultraviolet light, the color change takes place to red or blue based upon the kind of disk selected. Both physics, as well as chemistry based analyses, are been performed. In the physics based analysis, the blocking of ultraviolet light rays is measured usually by performing the color related experiments on a computer.

In particular, the images of control, as well as the test groups of the disks are taken out with the help of a digital camera. The disks are exposed to a known amount of UV light. On the exposure, disks change the colors. The change in the color, which is said to be proportional to the amount of the absorption of UV light, is found out by measuring saturation of color. Later quantitative experiments are performed for large numbers of images and the results are said to be evaluated based on the composition of chemicals present in sunscreen.


As per the results obtained from the experiment, the Combinations of various ingredients and the SPF has a significant effect based on the efficiency of the sunscreen.

The Standard protection factor of any sunscreen and the chemical composition are two most important considerations while deciding as to which sunscreen can be used in different environmental conditions to block the UV light rays.4

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Practise This Question

Fundamental properties which determine the state of a system are referred to as state variables.