Hmmm looks like better NiMh chemistry in hotter temp is the case. For the Jetsolis the voltage could be too high for the boost driver that better battery chemical reaction is not enough to boost the runtime.
Standardized testing of batteries is done at 20°C to 25°C, but most batteries (including NiMH and Li-Ion) actually work a bit better at higher temperatures. At temperatures of around 40°C to 45°C (or even up to 60°C) the voltage level is higher and you get slightly more capacity and a decent amount more energy out of the cell. This info is unfortunately not in the Eneloop datasheets, but I found a graph which was on the eneloop.info website back in the day.
Some datasheets of Li-Ion batteries (e.g. the UR14500P datasheet) have such a graph included.
While higher temperatures are good for getting the maximum out of the cell, they are also detrimental to the life of the battery, but that is of course a different topic.
I have seen the same thing testing batteries at higher currents. The warmer the battery the better it will perform.
If you run a capacity test on the same cell twice and don’t give the cell a rest after the first test after charging the cell, It’s warm from the test and charge. It will tend to have better performance on the second test with usually less voltage sag and higher current. I have noticed it most with the smaller cell sizes.
In all type of cells, being based on a specific chemistry, benefit from higher temperatures in terms on internal resistance along with capacity because of the faster ion movement permitted by higher temps. Although in terms of current provided, it obviously has its limit because of electrical conductivity dropping with temperature.
So don’t push it say above 40-45C, except for high discharge cells, for good cycle life obviously.
This can be used in a certain way to actually be beneficial though:
When discharging in cold weather, internal resistance is increased. However, heat dissipation is increased. So, as you discharge the cell in colder weather, performance actually gets better
OK, the prototyping is final. Below are the runtimes for Jetusolis and JetuE21A compared to stock XPE2. All measured in cooled 25° condition to avoid fluctuation in battery capacity as encountered earlier,
I will post the beamshot with alternate optics later.
Those look good to me. Very reasonable compromise in output for the significant improvement in CRI.
Since the 5000K Optisolis uses a 420nm diode, compared to the more conventional 440nm diode in the warmer Optisolis variants, with a consequently higher forward voltage, I’m guessing the warmer versions will consequently run a little bit longer at the same current.
Only up to 10°. At very close range this 10° with its rectangular tight spill already creates some artifacts, the 5° will be worse I guess. The narrow spill is very useful in cases such as mouth or nostril inspection where you don’t want too much glare to the patient. I myself prefer the 20°. The stock optic has bad yellow tint shift ring around the hot spot.
I have tunnel vision, field of view well under 10°, so I’m always on the lookout for lights that put all the light where I can use it. 10° would still be pretty good, though