What causes an LED flashlight to go dim suddenly?

I have this new two-CR123 batteries flashlight that uses LED heads. The batteries are new. So I was more than a little surprised when the LED light suddenly went slightly dim.

I checked and found out that sometimes three LED heads would light up, sometimes four. The final outcome is the LED light is not as bright as before.

Is there a bad connection somewhere?

GOLOK,
Welcome to CPF!

It would be useful to know which flashlight you are talking about. It would also be useful to know whether replacing the batteries with brand new 123A's makes any difference.

It could be a loose connection or dirty connection.

Al

Yes, I agree, if three out of four light, and that one sometimes works, sometimes not, the most likely problem is a bad connection of that LED.

Unfortunately, the defect could be inside the part itself.

Doug Owen

Hi Golok!! Glad to see another fellow CPFer from PJ, MY too!! I'm assuming you're the same from Bladeforums? Welcome anyway!

Hmm.. as far as I know a LED light would sorta flicker then go dim, which is typically going into 'moon' mode from 'sun' mode. However you mentioned new batts so thats a bit of a puzzle. Al's right, might help more if we know what brand of light it is...

Hmm, I'm assuming that there's a sufficiently highly rated resistor in there, and that the LED's aren't dimming due to overdrive/overheating. (Would probably be most noticable with new batts, especially if you got a cell with an inordinately high voltage - happened to me once, took out a cheap laser pointer before I spotted it though!). Though if you've had the light for a while, I guess that would have been noticed before, and I doubt that 1 LED would behave differently to the rest, so I'm probably wrong.

Sounds like the most likely candidate is a dodgy connection. Which light is it we're talking about here?

I had this problem in one of my torches. As the torch gets caried around the batteries get jostled around inside the battery tube. This rubbing together often causes the contact surfaces on the battery cells to become pitted and tarnished, increasing the resistance. The result was a torch that would go into "moon mode" without warning. Two-cell torches are more prone than three- or four-cell torches. LED's, being very sensitive to voltage and current loadings will fo from full rrightness to hardly on at all in less than a volt difference. Torches fitted with a booster circuit will atempt to overcome the problem by drawing more current, but the higher resistnce will not allow it to draw more, so eventually the booster can't cope either.
The remedy...before you throw out those batteries, remove them from your torch and give the contact surfaces a good clean to remove any oxides. Then place the batteries in a different order in the torch so that at least two of he cells have different contact points than they had before. I've gotten several days more hard usage out of apparently "dead" cells by using this method!
Other sources of intermittentcy: Switch contacts. Again it is mainly 2 cell torches that suffer from this condition.
Poorly fitted torch body components such as rear end covers and springs.
Loose or tarnished contact rings.
Another cuse of apparen torch failure is using your torch on nicad cells which have a lower voltage than dry cells. They also "Die" suddenly and sometimes unexpectedly.
These are just a few ideas that come to mind!

There may be problems with 123's. Some die during non-use and don't deliver their "promised" life. Take note of your experience and re-post if you have info that may be helpfull.

123 lithiums may have some problems - could it be "flash" testing? If so they are not very robust or dependable cells.

CPFers what is your 123 experience?