5*Cree R2 1200-Lumen intensity

[diverdave]

If I use a large single cell 3.4 volt but high amperage how much dimmer will my light be or will 9watts however you get it yeild same results 1200 lumen 5 cree r2it says it will run from 3.2 to 8.4 volts

 

[DIWdiver]

It depends on the driver. If your driver can still put 9W into the LED, then the brightness will remain the same. If you have a buck-boost, sepic, or similar type driver you will be fine. I think TaskLED makes a driver like this.

But most drivers are buck type switchers, and once the battery voltage falls down close to the LED voltage, the output will begin to reduce. Trying to put precise numbers on it is impossible, as there are way too many variables, but I'll give you some ballpark figures. At 9W in 5 LEDs, (1.8W/led) the LED voltage is typically 3.4V and current around 530 mA each. So while the battery voltage is 3.4V or higher you may get full or nearly full output. But as it drops below 3.4V the output will begin to dim. All buck drivers need at least a little voltage differential (battery voltage a bit higher than the LED voltage). Single-cell lights with buck-type drivers typically use LiCo or IMR cells, which keep the voltage above 3.7V for a good portion of the usable charge, giving you this differential. Also, you could have LEDs with above average voltage, which would make things even worse.

If you know anything about the driver (or maybe the light it came in), it could help pin down the answer you want. Someone here is likely to recognize it.

 

[lautmaschine]

The driver that comes with that package is well-known on these boards. Out of the box, mine had a forward amperage of under 700mA, and you probably require 1A to get close to the 1200 Lumen output as advertised. You can do that by replacing the board entirely or modifying the sense resistors on the existing board (and ensuring you have good heat sink transfer).

As far as batteries go, you will want two batteries in series, for 7.4v+, and given the power consumption (up to 19-20watts, depending on driver), I would suggest some cells in parallel. I use a 2S4P 18650 pack, and that is plenty of battery for me.