Light

Mustard plant, flower,

Photograph of a Mustard plant taken at Glasnevin Cemetery

Copyright John Kennedy

Mustard plant, flower,
Copyright John Kennedy

Mustard plant, flower,

Photograph of a Mustard plant taken at Glasnevin Cemetery

Copyright John Kennedy

Enlarge image

Light can make things happen. It helps plants to make their own food. How do they do this? Carbon dioxide in the air combines with water to form oxygen and a kind of sugar. This is called photosynthesis; and it only happens when there is sunlight. Chlorophyll in the leaves of plants is also needed.

This is one of the most important chemical reactions in the world. If there are no plants then we cannot eat; for even if we eat meat, the animals first have to eat plants or grass. So if the sun burns out the world ends! But there is no need to worry as this will not happen for millions of years!

Some things, like glass, water and some kinds of plastic let light through them. These things are called TRANSPARENT if you can see clearly through them (like you could read some writing through them).  

Other things, like many bathroom windows, let light through them, but you cannot see clearly through them. These things are called TRANSLUCENT.

Then there are very many things that let no light through at all. These are called OPAQUE. Most things are opaque – like tables, chairs, walls, the ground.

Diagram of an eye

Eyes: light goes into your eyes through the round black hole called the pupil. The jelly-like lens at the front of your eye then focuses the light on the retina at the back of your eye.  A special nerve connects the eye to the brain to tell you what you see.