UV light ranges from about a 100 to 400 nm in wavelength, and is further categorized as UV A, B and C (another way of classifying UV light is Near, Middle, Far, Vacuum and Extreme). The smaller the wavelength of UV light, the more energy it carries and the more dangerous it is. UVB and UVC are both extremely harmful to living things and are mostly blocked by the Ozone layer in the atmosphere. 98.7 percent of UV light that reaches the Earth’s surface is UVA. The light from a Black Light consists of UVA radiation. Excessive exposure to all forms of ultraviolet radiation can cause many harmful effects in our skin.
Overexposure to UVB can cause sunburn and damage DNA which can lead to skin cancer. UVA, B and C can all damage collagen fibers and hence cause our skin to age faster. Both UVA and B destroy vitamin A in skin. It is important that a screen protect against all different forms of UV.
While overexposure of UV light has many harmful effects, it is also beneficial. UVB light induces the production of Vitamin D in skin, which is essential for healthy bone growth.
1 Black Light
Assorted UV-sensitive beads
Transparency film or acetate sheets
Spatula or butter knife
Fig. 1. The EM Spectrum
UV-sensitive bead demonstration:
The presence of UV light in our atmosphere can be demonstrated using beads that are sensitive to UV light (available at ).