Infrared radiation is associated with heating and is emitted by bodies; infrared cameras detect its intensity. Visible light is the part of the EM spectrum detected by our eyes and is used in illumination and fibre-optic communication. Both are electromagnetic waves; whether they are absorbed, transmitted or reflected depends on the material and wavelength. Example: Explain heating by an infrared heater. Absorbed radiation transfers energy into a body’s thermal store. Distinguish the quantities.