1.   Clouds do not block UV rays.

2.   High in the atmosphere, however, naturally occurring ozone is essential for life, blocking ultraviolet rays that would fatally mangle DNA.

3.   I have heard of a film that can be applied to block the rays.

4.   In the stratosphere, ozone blocks ultraviolet rays from sunlight -- a major cause of skin cancer -- but global levels have declined gradually for over a decade.

5.   Skyscrapers block sun rays, back yards are unheard of, and not so much as a weed sprouts through the cracks in the sidewalk.

6.   Solar screens, tinting, awnings and window treatments can block unwelcome rays and decrease solar heat gain.

7.   The low-emission films are also effective for blocking ultraviolet rays, and they offer excellent outside visibility.

8.   They are more economical and environmentally friendly because they use shade to block the rays of the sun and ventilation to pull the hot air from the house.

9.   They are not as effective for reflecting heat rays as the less expensive reflective films, but they are as efficient in blocking ultraviolet rays and in reducing glare.

10.   While ozone in the stratosphere helps block ultraviolet rays, it is harmful when concentrated closer to the ground.