LED FORWARD CURRENT & VOLTAGE

If you don't know any of the forward voltage, current or power, I see no way to determine these parameters. If you know any one of them, you can find the other two.

Edited to add: The basic problem is that the LED will operate at above the rated power form some period of time, then fail. If you don't know any of the limits you can only keep increasing them until failure, and then that only gives you an upper limit on the parameters.

Bob

 

BobK is right, you can't determine the LED's power rating through measurement. You could measure the temperature rise and use that as a guide.

You're measuring the parameters the right way. You need to understand that LEDs are primarily current-driven devices. The voltage you measure across the LED doesn't vary much over a wide range of currents. The power dissipation in the LED is equal to the current flowing in your circuit multiplied by the voltage you measure across the LED at that current.

If you're measuring 3.1V at a forward current of 170 mA, you can assume that the LED's forward voltage is ABOUT 3.1V and calculate the current you need based on the wattage. P = V I (power = voltage times current), so I = P / V. If you assume P is 0.5W and you know V is around 3.1V you can calculate I (current) to give that much dissipation. P / V is 0.5 / 3.1 which is about 160 mA as in your drawing. So you are running the LED at 0.5W already.

Now I would measure the temperature of the heatsink (does it have one?) and if this seems low (say under 50 degrees C), increase the current. But without knowing the specification of the LED you can't be sure you're within its limits for the long term.

Find some data sheets for similar LEDs and see what they say about operating temperature to get some idea of how hot they're supposed to run.

That's all I can suggest. Good luck!