An LED driver is a self-contained power supply that controls the amount of current and voltage supplied to an LED light. An LED constant current driver monitors the loop current of each LED and automatically adjusts the generated DC voltage output to the minimum value needed to produce the highest forward voltage. As mains power is Alternating Current (AC) and Light Emitting Diodes run on Direct Current (DC), this current needs to be converted by a rectifier. Some LED lamps have inbuilt rectifiers so can be used with iron-core transformers. If there is no inbuilt rectifier then the LED light needs to be used in conjunction with an LED specific driver as they all have rectifiers as standard. Some LED Drivers use Pulse Width Modulation (PWM) in conjunction to enable the LED light to become dimmable.

Iron-core transformers are the old type of transformers that are made by winding two wires around an iron core. This produces an unregulated 12 volts of AC which will drive an LED sufficiently provided there is a rectifier in use.

Another type of transformer is the electronic transformer which contains an inverter which allows the size of the actual transformer to be reduced. The electronic transformer uses a high-power switching semiconductor to interrupt the mains voltage at a high frequency and had been designed to work across a wide range of power loads. The average electronic transformer will be specified for a load range of 20 to 60 watts, which means that it will operate within its specification only when connected to a load which is somewhere within that range. Because LED lights draw so little power, they will not reach the minimum voltage of an electronic tranformer.

To get the best result of high brightness and long lamp life of 80,000 hours+ from an LED light, it is highly recommended that it be used in conjunction with an LED constant current driver. This driver delivers the exact current required by the LED and will make the lamp work over a range of voltages. Without a n LED constant current driver the lamp would be sensitive to voltage changes, by getting dim or going out if the voltage drops too low, and the lifetime of the lamp will be reduced if the voltage goes too high.