This I how estimate where I want to be with current or just to see how many lumens I should be making at a certain current. A few members here have already give us a guide with their led test data. Most test are done on copper mcpcb attached to a big chunk of aluminum, usually the tester has provide the information on how the test was performed in the data.
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If using a direct drive driver or FET driver you can also look at battery discharge graphs to match the vf of the led at a certain current to estimate the output of the led.
Say you have a battery that at 5 amps of load sags to 3.7v, now go look at the led test data and see where the vf becomes 3.7v if its at a current of around 5 amps then that’s the estimated output. As long as the battery voltage is above the vf of the led the current will climb until they meet or the led blows if its more than the led can stand in direct drive. With direct drive or FET your looking for the place where battery load voltage is equal to the led load vf at a certain current. The test data is a very useful guide.