Re: Help: How much resistance? SYOL, 2 CR123, 800
I believe that Vf of Luxeon III is measured at 700mA. So, the Vf at 800mA could be slightly higher. Also, because the battery voltage sags at 800mA load, the required resistance should be lower than 2.7 ohm. I actually estimate 1.5~2.0 ohm depending on battery brand and LED variance.
I suggest trying various resistors between 1.5~2.7 ohm and measure the actual current. You will need 2 watts resistors.