Both are invisible light on either side of the visible spectrum. Infrared lies just beyond red — longer wavelengths, lower energy, felt as heat. Ultraviolet lies just beyond violet — shorter wavelengths, higher energy, which is why it causes sunburn and damages DNA while infrared does not.
The core difference
Two invisible bands on opposite sides of the light we can see.
- infrared — beyond red; longer wavelength, lower energy. Thermal imaging, remote controls, heat lamps.
- ultraviolet — beyond violet; shorter wavelength, higher energy. Sunburn, sterilisation, fluorescence.
The prefixes say it
Infra- is Latin for below and ultra- for beyond — below red and beyond violet, in terms of frequency. Since red is the lowest-frequency light we see and violet the highest, the naming is consistent once you know which end is which.
Why only one is dangerous
Energy per photon rises as wavelength shortens. Ultraviolet photons carry enough energy to break chemical bonds and damage DNA, which is what causes sunburn and skin cancer risk. Infrared photons do not; they deposit energy as heat, which is why an infrared lamp warms you without the same risk.
Frequently asked questions
Which has more energy, infrared or ultraviolet?
Ultraviolet. Shorter wavelengths carry more energy per photon, which is why UV can damage DNA and infrared cannot.
Can humans see either?
No. Both fall outside the visible range, though we feel infrared as heat. Some animals, including many insects and birds, can see into the ultraviolet.
Why is it called infrared?
Infra- means below — it sits below red in frequency. Ultra- means beyond, so ultraviolet lies beyond violet.