LED drivers regulate power to an LED or LED string. LEDs perform optimally only when fed with constant DC voltage. Individual LEDs used for illuminative purposes require 2-4V DC power, and LED arrays require higher voltage. Light output from a LED is proportional to the current, and changes in voltage may cause the light output to vary. When current exceeds the optimal limits the LED becomes brighter, and when temperatures increase the light output degrades rapidly, leading to shorter life. The LED driver ensures the LED or LED string receives a constant level of power, and thereby protects the LED from line-voltage fluctuations. The driver has pulse-width modulation circuits that dim the brightness and protect the LED from the ill-effects of high temperature. LED drivers also offer colour changing and sequencing functionality. These LED drivers find a wide host of application in most types of LED lighting systems, smartphone camera flashes, signage and display backlighting, automobile tail lights and more. LED drivers work as the power supply for LED lights and are available in many types, differentiated by supply and output voltage, output current, the power and the form-factor. Many LED drivers are compatible with almost all commonly available LEDs, but some drivers are only meant for specific LED devices or arrays.