Electromagnetic Spectrum The sliver of light waves visible to humans as a rainbow of colours from violet-blue to red is bounded on the short end by ultraviolet rays, which honeybees can see, and on the long end by infrared waves, upon which night-vision equipment operates. Someone wearing night-vision goggles, for example, can detect another person’s body heat in complete darkness. Light waves are minute, but the scale along the bottom of this chart offers a glimpse of their varying lengths, measured in nanometres (nm). (1 nm = 1 billionth of a metre)