When UV lights are turned on, they do get hot, but not as hot as an incandescent bulb. On average, they reach about 50 degrees Celsius (122 degrees Fahrenheit). UV-C LEDs generate more heat than mercury-based lamps, so it is important to manage the heat properly to ensure the longevity of the system. This can be done by implementing thermal reduction techniques and heat monitoring.
Ultraviolet rays are neither cold nor hot, but when they are absorbed by any object they tend to heat it up. On the other hand, infrared rays are associated with heat and can show us if the object is hot or cold. Fluctuations in water temperature can affect the power of a conventional UV lamp and, therefore, its ability to achieve the required UV dose. When light hits an object, the wavelength of the light must resonate with the particles present in the object. The object absorbs the light and converts shorter wavelength light into longer wavelength heat.
Infrared light is part of the electromagnetic spectrum and its wavelength is slightly shorter than that of red light, which is a component of visible light. Heat can be transformed into light energy and light can also be transformed into thermal energy. LEDs emit all their light on the front surface of the device and heat on the back surface, while mercury lamps emit light and heat through the same surface. UV LED systems can be designed so that they do not transfer heat to the water, thus reducing fouling rates and ensuring a constant emission of UV rays regardless of the water temperature.