Focus Zoom Lens Cree Q3 Flashlight $8 at Meritline

I got this flashlight a couple months ago from Meritline. Took a while to arrive since it comes straight from China. It's a very nice flashlight and extremely bright, *when the battery is fresh*. This thing eats AA batteries like there's no tomorrow. If you're down with some nice rechargables or simply purchase AA's by the bushel (I know I do), it's hard to beat at this price.

#1 there is probably a modification you could do to decrease current, if you're handy with small tools and have a multimeter. Light output is seen by the eye on a log scale and as current is lowered, forward voltage required drops too, as well efficiency rising as current and temperature drop.

The result is that if you put half as much current through the LED the battery will last at least twice as long but you will be closer to 100% light output than to 50% light output. For example, a light driven to 250mA needs about 3.2V to do that, when if it were driven to 1000mA it would need closer to 3.75V.

In the former case, 0.25A * 3.2V = 0.8W. In the latter, 1A * 3.75V = 3.8W. It takes roughly (3.8W/0.8W=) 4.8X as much power to make the light look slightly less than twice as bright.

First what you'd need is to non-destructively remove the LED driver board from the head of the light. Sometimes it just pops out. Other times you need a pointed tool like a pick to get into a hole and rotate it out along the threads inside the head. Other times it's glued in and you need to boil the head to soften the glue before prying or rotating it. There is a chance it will tear a wire from the driver board to the LED, I only advise trying to modify it if you have a soldering iron and spare piece of wire in cause it does tear and needs soldered back with replacement wire.

Once the driver board is out, connect the battery and measure the voltage at the LED's pads, OR measure the current going from battery to LED, or desolder a power lead to the LED and measure current from driver to LED.

If you measure voltage at the LED's pads, use the Cree datasheet for that LED emitter type to find the forward current @ voltage (you measured), and to find the lower, target voltage at the current you desire to reduce the light to.

If you measure current from battery or to LED instead, it's more straighforward math pick the new lower current you want.

I have several of these. Never had a problem with battery life.

^ Depends on how long you need it to run, if there's a problem. On a good quality (low internal impedance) NiMH cell, the current draw is over 2000mA, meaning about an hour of runtime or less (NiMH capacity is rated down to about 0.9 to 1.0V while many single-cell-alkaline/NiMH powered lights start dimming or stop working completely at 1.0 to 1.1V).

If using an alkaline cell with higher internal impedance, it will suffer a higher voltage droop towards the later 2/3rds or so of the battery capacity, meaning it reaches that ~ 1.0V cutoff point sooner in the total capacity curve. Sometimes with alkalines in a single cell light, if the light gets dim, starts blinking or cuts out, all you have to do to get a few more minutes of light is leave the light turned off for awhile so the cell recovers.

Personally I'd rather avoid these issues and no longer buy lights without at least one mode that both produces over (roughly) 25 lumens and can do so for > 2 hours (or more lumens on a larger light) but someone else might have different needs.

Also, two different specimens of light can drain their batteries at different rates due to small differences in LED forward voltage, more significant differences in tolerance of the driver feedback resistor (typically a +-10% tolerance part), and differences in quality control resulting in better or worse electrical contact between battery/end cap/body tube/head/driver PCB. Sometimes just stripping a light down, cleaning it out and cleaning oxidized aluminum away with a steel wool pad will increase current and brightness.

This is unquestionably the best under-$10 flashlight available today. I keep buying them, and giving them away, and buying more. In for another handful...

Agree that this is by far the best under $10 flashlight. No battery problems here and I have several. The wide zoom is ultra functional.

this is the best one out there, use rechargeable batteries.

This thread is an epic DaveC treatise on LED lights. Dave is the penultimate flash light geek, and I mean that as a sincere compliment.

I've collected more than 100 flashlight over the years and this is the only one that I don't leave the house without. Bright, well built, and the zoom is handy. I get 1-2 weeks of daily use when using a good NiMH. This thing is an absolute steal at 8 bucks.