Realistic runtime testing for LED lights?

[KDOG3]

I've noticed that most runtime test are done where a light is turned on and left on continuously until it drops out. But I would be willing to wager that 95% of the time, lights are used only a few minutes at a time. I wonder what the actual runtime of a given light would be (say, the E2DL I have on the way) if there were a way to test it in a way that has it run for 5 minutes then off ten and repeat until it drops out. Or could we come up with a percentage of longer runtime from intermittent use rather than full on until dead use? I'm just curious...

 

[saabluster]

I've noticed that most runtime test are done where a light is turned on and left on continuously until it drops out. But I would be willing to wager that 95% of the time, lights are used only a few minutes at a time. I wonder what the actual runtime of a given light would be (say, the E2DL I have on the way) if there were a way to test it in a way that has it run for 5 minutes then off ten and repeat until it drops out. Or could we come up with a percentage of longer runtime from intermittent use rather than full on until dead use? I'm just curious...

It is a good idea but you'd have to get everyone on the same page. That's the hard part. It's not very practical though as it is more difficult to test like that because now each test takes 2-3 times more off of your runtime.

 

[PhantomPhoton]

I agree somewhat. I'd love to see the differences between continuous and intermittent runtime. The thing is the extra time it would take CPF reviewers to do this. Plus I agree that getting everyone to agree upon a standard would be tough. 10 minutes? 5 Minutes? 13 minutes and 26 seconds per burn?

On the other hand, I generally use lights continuously, or at least in time spaces consisting of hours. As a nocturnal outdoor enthusiast I personally find continuous runtime tests to be very relevant.

I'd assume that LEOs may also want continuous runtime tests as it establishes a minimum runtime. Breaking up the runtime should extend the burn time slightly so having the bare minimum is an essential standard to know.

 

[Light Sabre]

Another thing good to know about a flashlight from continuous runtime tests is how long the flashlight runs until it falls out of regulation and how long does it run after it falls out of regulation. Some just abruptly shut down with no warning and no light at all. Some have a gradual declining brightness until the batteries are finally too low to supply any more current. Knowing how long you have any amount of light after a flashlight falls out of regulation is a good thing to know. Is it a couple minutes or is it several hours. One of my flashlights will run 24 hours at full output and then gradually dim for another 4 days. This is assuming that you're testing with alkaline, NMH, NiCad, or Lithium primarys. Protected Li-Ion batteries are another story all together.

 

[PeaceOfMind]

Or could we come up with a percentage of longer runtime from intermittent use rather than full on until dead use? I'm just curious...

Seems like everyone is pretty sure that the runtime would be longer with intermittent use, rather than shorter. What is the reasoning behind this?

I'm not sure myself, but was just thinking that, as the light heats up, the internal resistance of the battery should drop, as will the LED forward voltage. Plus, depending on the electronics, there may be some additional start-up current for the driver/controller that will have to be expended at each turn-on. These factors I would think point to less run time with intermittent use.

However I am sure there are plenty of things I am not accounting for, and I'm not overly sure about the above

 

[Marduke]

Batteries do better in short bursts, with time to rebound. The "alkaline mythbuster" test of the Proton Pro illustrated this well.

 

[jupello]

These would be pretty interesting figures to see, especially the tests with alkaline batteries since they suffer most from the continuous tests.
I started thinking that it should be possible to make pretty accurate formula for calculating those intermittent runtimes based on the continuous runtime, current draw from the batteries and battery chemistry.. but that would require knowing/testing how the batteries behave under different conditions first.

 

[McGizmo]

.....
I'm not sure myself, but was just thinking that, as the light heats up, the internal resistance of the battery should drop, as will the LED forward voltage. Plus, depending on the electronics, there may be some additional start-up current for the driver/controller that will have to be expended at each turn-on. These factors I would think point to less run time with intermittent use.

......

My gut also tells me that intermittent usage will see a shorter overall runtime. I base this on tested runtimes at different ambient battery temperatures (primary lithium) and significant advantages when the temperature was elevated due to the light being on and heated up.

Does anyone keep track of the elapsed time they operate their lights if the usage is intermittent? If you knew for certain that you could get 1.5 hours of run time out of your light based on how you use it, would you have an idea of how much time was remaining in the battery? I know I wouldn't! :nana:

 

[PhantomPhoton]

It could depend upon cell chemistry/ type. I believe that the difference in runtimes especially on high power, will be very small but in favor of intermittent use.