Not all the same light
Stand in noon sun. You feel more than you see.
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The rule
Ultraviolet can harm, and ozone absorbs most of it. Visible light feeds plants. Infrared carries much of the Sun's heat.
Absorb means take in. The ozone layer is ozone gas high in the air.
- Ultraviolet, visible and infrared light arrive together.
- The ozone layer stops most of the ultraviolet.
- Visible light reaches the ground.
- Infrared carries much of the heat.
The idea
Sunlight is a mix of electromagnetic waves. Nearly all of its energy is in three kinds. These are ultraviolet (UV), visible and infrared (IR) light. You feel infrared as warmth, but you cannot see it.
| Kind | What it does |
|---|---|
| Ultraviolet | Carries more energy than visible light. Can harm eyes and skin. Ozone absorbs most of it. |
| Visible | Reaches the ground. Feeds plants for photosynthesis. Also warms what absorbs it. |
| Infrared | Carries much of the Sun's heat. The warm ground sends heat back out. |
A wavelength is the distance from one wave crest to the next. A crest is the top of a wave. UV waves are shorter than 400 nm. Infrared waves are longer than visible light waves. One nm is 10⁻⁹ m. Some water purifiers use UV to kill germs.
Other waves come from the Sun too. Gamma rays and X-rays do not reach the ground. Air absorbs them high up. Microwaves and radio waves carry little of the Sun's energy.