If humans cannot see ultraviolet waves, how can ultraviolet light be used to gather evidence of a crime?

ultraviolet light detects the presence of radioactive substances.
ultraviolet light shows cold areas as blue and warm areas as red.
ultraviolet light causes substances to fluoresce and give off visible light.
ultraviolet light transmits information to am and fm radio receivers.

Ultraviolet light causes substances to fluoresce and give off visible light.

Explanation:

Ultraviolet light is a part of the electromagnetic spectrum that includes electromagnetic waves which have wavelength just shorter than the visible light, so they are not directly visible to human eye.

Fluorescence occurs when ultraviolet light hits the atoms of some substances: the electrons in the shells of the atoms gain energy (absorbed from the ultraviolet radiation) and jumps to higher energy levels, then they de-excite re-leasing part of the energy back, but in a different wavelength region, corresponding to visible light. Therefore, these substances absorb radiation in the ultraviolet region and re-emit radiation in the visible light region.

conduction, convection, radiation