So I’ve been asked this alot, thought I’d make a small note for the benefit of others
An XM-L2 LED for example is “10W capable”, but it can also be run as a 5W LED, a 3W LED, or even as a 1W LED.
Wattage (or power) is a measure of how much energy is consumed through the LED each second. In terms of volts and amps, power is volts multiplied by the amps.
A “10W capable” LED then like the XM-L2 for example, can be run at 10W, 5W, 3W, 1W or any other power level it supports up to it’s maximum. The exact wattage it runs at depends on what current flows through it, and that is usually determined by what driver you use to power it.
The maximum current supported by the XM-L2 for example, is 3000mA (or 3A, or 3 amps). The voltage of the LED when running at 3A is 3.37V (according to the specs from CREE). 3A multiplied by 3.37V equals 10.109W to be exact. So the XM-L2 runs at 10.109W at it’s supported maximum.
If instead of being run at 3A, the LED is powered off a 350mA (0.35A) driver for example, then the power consumed through the LED will be 0.35A multiplied by 2.82V (the voltage of the LED is lower at a lower current) which equals 0.987W (about 1W).
When powered off a 1000mA (1A) driver, the power will be 1A multiplied by 3V, which means 3W will be consumed through the LED in this scenario.
On a 1500mA (1.5A) driver, the power will be 1.5A multiplied by 3.1V, which equals 4.657W (about 5W).
So to answer the question is this LED 10W, 5W or 3W?, the answer is it depends on which current you run it at and that usually depends on which driver you choose to power the LED with.
3000mA driver - 10W
1500mA driver - 5W
1000mA driver - 3W
350mA driver - 1W