Insects see light in the ultraviolet spectrum, but humans only see it with the help of special equipment.
When people refer to ultraviolet (UV) light, they usually refer to the UV spectrum. A spectrum is a range of wavelengths rather than a specific wavelength. The UV spectrum is just a part of the entire electromagnetic (EM) spectrum; is located just above visible light if the different categories are classified according to energy. There are several subcategories of UV radiation, including near, medium, far, vacuum and extreme. Ultraviolet light is important for human health because it is an important source of vitamin D, but it can also increase health risks such as skin cancer.
The sun emits a range of ultraviolet frequencies.
The electromagnetic spectrum is a system used to describe light of different wavelengths. Visible light is just a part of the spectrum, which ranges from low-energy radio waves to high-energy gamma rays. The UV spectrum has a shorter wavelength and a higher frequency than visible light and has a higher energy. Ultraviolet light is not just a part of a single wavelength; the UV spectrum ranges from a wavelength of about 10 nanometers (nm) to 400 nm.
The electromagnetic spectrum, of which light is a fraction, is a continuous distribution of wavelengths ranging from ultraviolet to infrared radiation.
This range of wavelengths is called ultraviolet because it is located just above the violet visible light section of the EM spectrum. Within the UV spectrum, there are several other subsections. Near UV, for example, is closest to violet light and includes radiation up to a wavelength of 315 nm. Extreme UV is at the other end of the spectrum and contains radiation between 121nm and 10nm. The shorter the wavelength, the higher the energy and frequency of ultraviolet light.
Light within the UV spectrum is emitted by the sun. Sunlight contains ultraviolet radiation in a range of frequencies, which is why it should be called the spectrum. Ultraviolet rays consist of radiation of higher energy than visible light, which is why they can cause sunburn. Certain types of fluorescent lamps can also provide artificial UV radiation.
Ultraviolet radiation can cause both positive and negative health effects. Exposure to ultraviolet light is essential for the body to produce vitamin D, for example, a nutrient that is difficult to obtain from diet alone. Ultraviolet light is also sometimes used to treat skin conditions such as psoriasis, although this form of treatment must be monitored carefully to avoid damage. Many people also use ultraviolet radiation to achieve a more tanned appearance. Overexposure to this wavelength of light can cause skin cancer, however.