Clarification of Digitally Rgulated Output or Why Did my Flashlight Dim ?

Hi, I have always recharged the batts on my lights before they get low before tonight.

Tonight, I noticed my Fenix TK21 was pretty dim at Turbo setting but it still cycled through the 4 brighness levels (just at a much dimmer level).

So I took out the 2 123's that came with the light and put in an 18650 and BOOM back in business.

I thought that Digitally regulated output maintained constant brightness and then just shut the light off when the batteries were too low to power the setting the light was on?????????

I was under the impression it kept it even until it was too low, then dropped the levels. That's how all my Fenix lights have been...

Drove me crazy with the new PD32(was only a very dim setting, changed the batteries and nothing happened... then I tested them with my DMM and saw they were all low including the 'new' batteries) because someone was dropping the used CR123A's back into the battery drawer! Who does that?!

Thanks, that makes sense.

Mabe it just had 3 modes and no turbo and I mistook it for 4 modes all at dimmer settings.

Different drivers (the circuit responsible for the regulation) handle this differently. Some will indeed keep the light running with a nice, even, flat output until the cell can't maintain it, then bam, it goes dark.

Some CPF members prefer this method, but I'd venture that most prefer a driver which allows for some type of "graceful" dimming when the battery can no longer maintain full regulation.

One method of gradual dimming is "stepped" regulation, where the light will maintain an even light output until some specified voltage, then drop down to a lower light level where it will continue to run in regulation for a while, then drop down to another lower level and run in regulation, and so forth. The graph for that looks like a set of stairs going down..... even, drop, even, drop, even, drop..... etc.

Some folks like to have a regulated light for their EDC, but will opt to have a direct drive (no regulation) light for their emergency light. The unregulated light will give them the maximum amount of time from the battery, and this is often preferable in a long power outage rather than having a shorter amount of regulated time.

Then, there are a few lights which actually offer a choice of regulation patterns so that the user can tailor the light's output characteristics to their current needs. Neat.

One of the controversies you'll find discussed in relation to regulated lights is what the cut-off voltage should be before the light cuts out, as this will directly affect the duration of light and also has an effect on the life of the battery.

All very interesting stuff, but mainly, understand that there is no one set type of regulation, and this is one of the things we discuss when deciding which new light to purchase.