The sun emits both visible and invisible electromagnetic radiation, including invisible ultraviolet light in the 290-320 nanometer band (UVB). Although the term "hard radiation" usually refers to penetrating high energy electromagnetic radiation in the X or gamma ray band, and ultraviolet light doesn't penetrate living tissue to the extent of these more energetic rays, it still causes significant tissue damage in plants or animals. In particular it can cause cataracts and cancers in humans, especially in the latter case in humans with light coloured skins, and in the former case in people of any skin colouration.

Most harmful ultraviolet radiation is absorbed by ozone in the earth's upper atmosphere, but some of it will penetrate the "ozone layer" and reach the surface. This level of penetration has increased since the mid 1970s due to the depletion of the ozone layer by industrial waste gases.

Plants and animals, including humans, produce pigments in their outer tissues to absorb ultraviolet light before it can penetrate their cells and damage their DNA, and the DNA itself has error correction mechanisms to repair the damage. However, like the protection provided by the ozone layer, this is not perfect. Some people can even feel when they're being exposed by a prickling sensation in their skin.

Further reading:

• Ultraviolet Radiation: How it Affects Life on Earth
• Ultraviolet Radiation and the INTERSUN Programme
• Ultraviolet Radiation: Ohio University Fact Sheet
• The Skin Institute: Skin Cancer
• Sun Safety and Young People
• Older Adults and Cataracts
• Wikipedia: Electromagnetic Radiation