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Light sources

Waves, sound and light · level 2, lesson 1 of 6

A question to start

The Moon shines brightly at night. But is the Moon really making its own light?

The idea

A light source is something that gives out its own light. The Sun, a candle flame, a light bulb and a phone screen are all light sources.

Lots of things we see are not light sources. They only bounce back (reflect) light that falls on them. The Moon is one of them: it shines because sunlight lands on it and bounces off towards us.

the Sun: a sourcethe Moon reflectsEarth
Gives out its own light Only reflects light
the Sun the Moon
a candle flame a mirror
a light bulb a white page
a phone screen a bicycle reflector

Worked examples

1. A dark room. In a room with no light at all, you cannot see a mirror or a white page. They need light to fall on them first.

2. A reflector on a bike glows brightly in car headlights, but it makes no light of its own.

3. Mars in the night sky looks like a bright, reddish star. It is reflecting sunlight, just as the Moon does.

Try it

  1. What is a light source?
  2. Is the Moon a light source?
  3. Name two light sources in your home.
  4. Why can you see Mars in the night sky?
Answers
  1. Something that gives out its own light.
  2. No. It reflects sunlight.
  3. Any two: light bulbs, a screen, a candle, a torch, a fire.
  4. Sunlight bounces off it towards us.

Common mistake

"Shiny things are light sources." A shiny spoon or mirror only bounces back light. Turn off the lights and it stops shining.

Where it leads