Which of these is not a source of light?

Light, or illumination, is a form of energy that travels in waves, like sound. Light is a fascinating topic to investigate in science lessons. You can find different sources of light, such as a candle or the Sun. You can also study reflection by looking how mirrors affect light. Refraction is something else you can look at. Refraction is when light 'bends' as it passes through different materials like water or glass. The light we can see, which is called visible light, is part of the electromagnetic spectrum. The electromagnetic spectrum includes radio waves, microwaves and x-rays.