Another use for a light meter, checking battery levels

I have been carrying some Rotary lights, modified to High CRI, that make over 350 lumens on a fresh 16340 battery.

Today I was using one of my Rotaries, and it seemed dimmer than usual, so I put the light on my light meter and it read 200 lumens. I then removed the battery and measured the voltage at 3.28v, so I put it on a charger.

A light meter lets me check if I need to recharge, without removing the battery.

When lumens drop by 50%, I usually notice, and my light meter is very useful for confirming whether it is time to recharge.

I like being able to check lumens, without having to open the light to test the battery.

here you see 391 lumens,

from a battery over 4v

my light meter is nothing fancy, I just put a cap from a vitamin jar over the sensor. I used an HDS to calibrate the meter, by adding a couple of pieces of paper under the white plastic cap.

The meter is surprisingly accurate, after calibrating it to a 200 lumen HDS, the meter correctly read the minimum lumen level of the light at 0.08… iow, the meter is accurate within the entire range of brightness of an HDS.

fwiw, sometimes I use unprotected 1200mAh IMR 18350 Keeppower cells, and the lights do not have any LVP built in.

I was concerned about overdischarge, so I did a test to see how low the lumens drop, when the battery is approaching overdischarge levels.

I found that with a battery depleted to 2.6v, the maximum output of my Rotary was just 15 lumens.

I find this very reassuring, since I will certainly notice if my light wont go over 15 lumens, and even at that level, the battery is not yet in danger of overdischarge. Plus an IMR is safer than an ICR cell, not as likely to vent with fire after a deep discharge cycle…

With a Protected ICR cell, I run the risk of tripping the protection and being left in sudden darkness, but with an IMR, I get lots of warning time to replace the battery, as the light keeps getting dimmer, without sudden darkness.

Nowadays' lithium ion cells are neither ICR nor IMR, not even when printed over an OEM wrap as a rule so much less on a false advertising rewrapper one (KeepPower IMR18350, for example). Check: Battery chemistry FINALLY explained @ Battery Bro

Flashlights using direct drive or linear mode drivers cannot overdischarge cells when using standard blue pumped white leds, this is because these emitter's Vf is ≈2.5V. This is something I've actually tested by leaving old cells directly attached to an emitter for days (current flow tapers and tapers tending to 0 a bit below 2.5V). So yes, really no point in using protected cells in them. Piss poor flashlights like SK68s pose a threat, though, as their drivers eventually switch to boost mode when powered with li-ion, and they continue drawing power from the cell like if it were a Ni-MH or alkaline.

Your method will not work with fully regulated boost drivers.

that battery bro link says:
Many of the high-drain batteries used in vaping and flashlights have IMR chemistry

Only works for lights with DD or crappy regulation.

thank you
sounds like a choice between long gradual dimming or sudden collapse
is it a feature or a bug?:slight_smile:

DD works for me,
it keeps me in touch with my unprotected cells

I know I can count on them, not to leave me suddenly alone in the dark

That is actually quite incorrect. IMR chemistry has a very low energy density, being the LG HB2/HB4/HB6 series probably the latest and final members among the big and better known players in this industry. The Samsung 20S, for example, is already an hybrid INR chemistry cell.

IMR is mostly a marketing moniker for the philistine crowd nowadays, just see how ridiculously often it is used by chinese cell rewrappers, often together with ludicrous and straight dangerous invented ratings.

Go ask Mooch, for example, and see what he has to say about this (he recently registered ;-) here).

I appreciate the comments that my light meter works to monitor battery drain based on the type of driver in the light

Matters not what the chemisty of the battery is for my light meter to pick up lumen reduction on my Jetbeam magnetic rotary