Runtime formula?

I just received one of the new Streamlight Protac 2L-X lights. The published spec are:

Using two CR123A batteries
500 lumens for 2hrs 45min
40 lumens for 30hrs

Using 18650 battery
500 lumens for 3hrs 15m
40 lumens for 30hrs

The above is with a 2600 mAh 18650. Is there a formula for calculating ballpark run time numbers using a 3500 mAh battery?

I come up with about 4hrs 30min (approx.) using basic math but I'm wondering if it's really that simple.

TIA

Tusk said:

I just received one of the new Streamlight Protac 2L-X lights. The published spec are:

Using two CR123A batteries
500 lumens for 2hrs 45min
40 lumens for 30hrs

Using 18650 battery
500 lumens for 3hrs 15m
40 lumens for 30hrs

The above is with a 2600 mAh 18650. Is there a formula for calculating ballpark run time numbers using a 3500 mAh battery?

I come up with about 4hrs 30min (approx.) using basic math but I'm wondering if it's really that simple.

TIA

Click to expand...

I'm certainly no 'Bill Nye The Science Guy', but...

You need to measure at the tailcap and see what drain you're getting with a freshly charged cell, or cells, on the various output levels.

With a typical Cree XM-L2 CW, you're pulling what...~3A at ~1050LM? 1.5A at 525LM? I have an XM-L2 U2 Redilast P60 that puts out 550LM right at 1.50A and I've measured that current at the tail, so we'll run with those numbers.

Say you run your 3500mAh cell down to 3.6v, about 50% discharged, that's going to cost you about 1750mAh, or 3+ hours. Now, if like the ANSI FL1 standard, you accurately measure output at 30 seconds after turn on, with a fresh cell(s) and take it down to 10% of that initial output, then you'll go longer.

Chris