High Power LED Driver Circuits

Step 2 Power LED performance data - handy reference chart

Below are some basic parameters of the Luxeon LED's which you will use for many circuits. I use the figures from this table in several projects, so here i'm just putting them all in one place that i can reference easily.

Luxeon 1 and 3 with no current (turn-off-point):
white/blue/green/cyan: 2.4V drop (= "LED forward voltage")
red/orange/amber: 1.8V drop

Luxeon-1 with 300mA current:
white/blue/green/cyan: 3.3V drop (= "LED forward voltage")
red/orange/amber: 2.7V drop

Luxeon-1 with 800mA current (over spec):
all colors: 3.8V drop

Luxeon-3 with 300mA current:
white/blue/green/cyan: 3.3V drop
red/orange/amber: 2.5V drop

Luxeon-3 with 800mA current:
white/blue/green/cyan: 3.8V drop
red/orange/amber: 3.0V drop (note: my tests disagree with spec sheet)

Luxeon-3 with 1200mA current:
red/orange/amber: 3.3V drop (note: my tests disagree with spec sheet)

Typical values for regular "small" LED's with 20mA are:
red/orange/yellow: 2.0 V drop
green/cyan/blue/purple/white: 3.5V drop

Comments

[doctek]

How did you make these measurements? One way I can think of is to put appropriate current limiting resistors in series with a led and measure the voltage drop across the led. Is that indeed what you did or is there a much cleverer method I'm missing?

[Nyxius]

LED are incapable of limiting current on it's own.  Therefore, voltage drop across the LED is dependent on total potential and total load in series with the LED.  Too much potential and not enough load means that the voltage drop across the LED will be high enough to "fry" the LED.  This is because LED have very small impedance compared to regular light bulbs. The voltages listed on the spec sheet are recommended drops that will ensure long lasting lifetime.