Surefire U2 low battery detection

[sbebenelli]

Does the U2 step down when the battery starts getting low? If so once it steps down how much battery is left to give decent light output?

 

[Kilovolt]

When the batteries are low the flashlight stays at the minimum level regardless of the ring position.

Personally, given the potentially bad behaviour of two CR123 in series, I never investigated the remaining runtime and at this point I always change the batteries. :shrug:

 

[chevrofreak]

It doesn't "step down" it just drops out of regulation and continues providing constantly dimming light.

http://lights.chevrofreak.com/runtimes/Surefire U2 (Dizzy)/

 

[Torque1st]

Low batteries and remaining life...

-One of the worst features of LED lights.

The human eye is very sensitive to color changes. With an incandescent flashlight we could always judge battery condition just by flicking on the light and observing the color. With an LED the color does not change with battery condition and the human eye can't really detect the output level differences. If the LED light does not do some strange things like flickering/blinking or turning on slow there is no indication you are about to be left in the dark. An LED user has to make sure they always have a backup set of cells handy. The situation is as bad as the old incandescent lights with bulbs that burned out... At least a spare bulb could be stored in the end cap or somewhere handy. People are usually SOL with a spare set of batteries. On the other hand it is easier to change out a set of cells on a dark moonless night than changing a bulb.

 

[z96Cobra]

Does the U2 step down when the battery starts getting low? If so once it steps down how much battery is left to give decent light output?

When the batts get low in my U2, I will get a fast flicker in the highest setting. If I then drop down a level, I can run it for a little while until that level starts to flicker. Whenever I get the flicker on the high setting, I just replace the batteries ASAP.

Roger

 

[greenLED]

With an LED the color does not change with battery condition and the human eye can't really detect the output level differences. If the LED light does not do some strange things like flickering/blinking or turning on slow there is no indication you are about to be left in the dark.

I'm sorry, but that's simply not accurate:

1. LED tint does vary with drive current. Lumileds, for example, bins their Luxeon emitters at given drive currents because output tint changes with drive current. All the Lux V's I've seen at work in the SF U2 will turn greenish at the lower light levels, and shift to other tints when driven at full power.

2. Human eyes can detect changes in brightness; they do so in a logarithmic scale, not a linear one (which is what regular light measuring instruments measure).

3. What the LED does when the batteries are low depend on the circuit used (and to a lesser extent on the batteries). Some LED constant-current drivers will shut output with no warning, but others will fall out of regulation and allow a long "tail" of diminishing output. If you have a constant voltage LED regulator (aka "semi-regulated" light), then the LED output will dim over time. Finally, if you are using protected li-ion cells, their built-in circuit may kick in and leave you in the dark once the battery "juice" becomes depleted. This may be totally independent from what type of circuit you are using in your LED light.

 

[Torque1st]

Sorry, but what an instrument can detect or show is not what you can detect with the human eye from a quick glance. Comparing a fresh set of batteries with an unknown can be done (I do it myself) for the very slight color change and greater light levels. Unfortunately that is not practical unless you carry two identical lights (one known good with fresh batteries). Sorting LED's at the factory is not comparable with detecting cell condition in the field. It is much easier to tell the condition of cells with an incandescent light. With an LED it is easy to be left in the dark with little warning. Keeping a bulky set of fresh cells around seems to be the only solution at present.