Some invisible wavelengths of light are longer than red. Radar, short for radio detecting and ranging, uses radio waves that reflect off objects. This is similar to how animals locate things using the echo of sound waves. The longest waves of the electromagnetic spectrum are radio waves. These waves carry signals in AM or FM codes. Microwaves are absorbed by water molecules in foods. Microwave ovens use less energy than regular ovens. Infrared waves are given off by all objects, depending on their temperature.