The following is absolutely no stab in the back of all the great cell testers on this forum. I respect all of them. In fact without reading a test I won’t buy a cell.
A lot of tests of cells on this forum. If those tests are (very) good, I’m sure many pay a small premium for them.
But why? Very often because a few percent more juice means a little longer runtime.
All very useful, but what I’m missing is tests of drivers.
A efficient driver may make a bigger difference in runtime than a cell that packs a few mAh extra.
I’m not just talking about drivers that are sold separately (by members) but also those part of flashlights.
Yeah, many flashlight reviews have runtime graphs which are a good indication. But no more that that because quality of cells may vary.
What to test?
Remove the cells and hook up a power supply. Let it run for 30 mins and write down the watts used. Also measure the lumens. Combined that would give a lumen/watt rating.
That’s useful for testing the overall efficiency of the flashlight. Surely an important number for me personally.
But it doesn’t really test the driver because the efficiency of the LED influences the numbers.
The only way I see to resolve that is by also measuring the watts delivered to the LED.
That sort of info is useful for people that just buy and use. But also for people who consider swapping components. The tests may show that certain swaps will be a downgrade.
Bad idea. Efficiency always depends from input voltage which is not fixed with cell powered lights.
Also, efficiency is not something that you can simply use for any calculations. If you have 1x18650 light and X 7135 chips driver you can calculate how long will it run with 10% or 40% or 100% and this rough calculations will be enough precision for real life usage. If you have bigger light with more complicated driver and various features like thermal regulation or ramping, any efficiency number would not help you to estimate lumens to hours ratio.
You could still measure the efficiency of the driver over various input voltages, output voltages, currents, temperatures. You’d get a huge number of measurements for sure, but you could condense them to some key numbers/indicators like “efficient for low brightness”, “not efficient at all” or something else people might think about.
I think it’s a great idea to measure those numbers, but probably a lot more work than most of us would be willing to do, and of limited usefulness.
Thermal regulation - causes problems, in practice limits tests to short bursts at different input voltages + interpolation.
Ramping - you can measure current, just try several and interpolate again.
For a flashlight, the total system efficiency is what matters. That is the emitter, driver, optics/reflector, lenses, wires and contact resistance and the effect of heat on those.
That’s why it is useful to measure the output over time in lumen hours for the complete runtime of the light. Knowing the total battery capacity in watt hours adjusted for different runtimes/current, it’s simple to calculate the lumens per watt which takes into account everything. Or at least approximates it very closely as long as your numbers are accurate.
But since it is rare that a light is used for prolonged periods from full battery to empty, it’s more pertinent to look at the system efficacy at lower levels.
Agreed, and I would love that sort of info in a standardized way. If the reviewers use different cells then total runtime can be misleading.
Say I buy a flashlight that is tested as having good efficiency, but it only has 3 modes and I want 5 modes. I could replace the stock driver with a driver that is extremely configurable. But I doubt I would do so if it turns out the new driver is 20% less efficient.
And yeah, I do understand testing can be difficult when thermal regulation kicks in on those super bright turbo modes.
Personally I need far less brightness. So tests at 300, 600, 1000 lumen would be what I would like to see. Those brightness levels often can be sustained for a long time.
Maybe the flashlight has a 2500lm turbo that steps down after a minute. Because that’s so short I don’t really care about that efficiency.
I did a few tests on drivers from led4power in the past:
I like to see a driver tested every now and then to see what its role is in a flashlight, as well as a reflector, a lens, a switch etc. , but I would find it boring to check all that in each and every flashlight, I agree that a total performance of a flashlight is more interesting than just what the driver does.