Ultraviolet radiation
Ultraviolet means “beyond violet”: the rays just above violet in frequency, which the human eye cannot see.
Insects such as bees have been found to be sensitive to ultraviolet. Sunlight contains a small amount of it, and it is also produced by electric discharges and mercury-vapour lamps.
Good for us
It makes vitamin D in human skin, so some exposure to sunlight is useful.
Harmful
Too much exposure can cause cataracts in the eye and cancer of the skin.
Uses
- Destroying germs in hospitals.
- Checking the hidden marks on banknotes: some chemicals glow when ultraviolet falls on them.
- Washing powders contain such chemicals, so washed white clothes look bright in sunlight.
Figure to be added