Strictly speaking, a black light is a kind of UV light. Black lights emit ultraviolet radiation (UV light). UV is radiation with a wavelength just shorter than that of violet light, which is the shortest wavelength of light in the visible part of the electromagnetic spectrum. The electromagnetic spectrum is the range of radiation from benign radio waves to highly dangerous gamma radiation.
Kinds of UV Light
Although many of us like tanning and spending time outside, UVA radiation is undetectable to the naked eye. UVA rays are the longest-wavelength, lowest-energy kind of UV radiation and the kind that is least harmful. It is the UVB and UVC rays in sunlight that causes the most damage. Prolonged exposure will eventually lead to sunburn and skin cancer. Especially if you're not using the proper SPF, or covering yourself when you're outside for extended periods of time.
Even though a sunny day is ideal, the sun is by far the strongest source of ultraviolet radiation in our environment. Solar emissions include visible light, heat and ultraviolet (UV) radiation. Just as visible light consists of different colors that become apparent in a rainbow, the UV radiation spectrum is divided into three regions called UVA, UVB and UVC. As sunlight passes through the atmosphere, all UVC and most UVB is absorbed by ozone, water vapor, oxygen and carbon dioxide. UVA is not filtered as significantly by the atmosphere.
The term black light refers to a specific kind of lamp, typically fluorescent, with a special phosphorescent coating that emits UV radiation in the UVA range.
Phosphorescence is a process by which substances emit stored energy slowly, in the form of visible light. It is often used in "glow-in-the-dark" materials (like the ones you played with as a child), which absorb energy through exposure to light and then emit it slowly in darkness, giving off a soft glow.
UV light also has other practical applications and artificial sources. A fluorescent lamp without the phosphorescent coating emits UV light in the UVC range--invisible and highly energetic. This light can cause damage to the skin with prolonged exposure but is commonly used as a disinfectant.
UV light is increasingly utilized in industrial and commercial applications. UV light-emitting diodes, or LEDs, are put to work in digital printing, where the light is used to cure printed materials. LEDs are used in traffic lights, indicator lights on airplanes and large stadium displays, due to their low energy consumption and small size.