18650 Lithium Battery Questions

[laur]

I have owned a Waion modified VB-16 light that uses a Seoul SSC "U" bin LED for about a year. Just recently I snagged an extra battery tube for the light. The electronics for the light allow for a voltage from about 3.5 volts to about 8.4 volts. After charging up my two lithiums (2600Mah and unprotected) I assumed that the increased voltage from two batteries would make the LED brighter. However, I didn't notice any appreciable increase in brightness when I turned the light on.

Reading the posts here at CPF, I thought that increasing the voltage increased the light lumens (Ex. -- Changing out a AA battery for the 14500 lithium ion). Maybe I am confused about the relationship of voltage and current to lumens.

My question is this. Does increasing the voltage to a LED increase its brightness level or do I need to go back for remedial training to Lumens University??

Thanks up front for explaining this mystery for me. There is such a wealth of talent on this forum, I feel humbled just being on the same Internet connection.

laur

 

[blackdragonx1186]

the way i would understand that is that with the higher voltage, its drawing less current from the batteries, thereby increasing the runtime.

 

[Marduke]

LED's require around 3.7v, and the circuit in the light either raises or lowers the voltage to that level. Voltage alone is not directly equal to how much "power" a light has. The circuit itself determines how bright the light is, and your choice of batteries usually affects runtime more than brightness.

I recommend reading the Welcome Mat, which has much more detailed info on how it all works.

 

[mdocod]

the buck style regulation will maintain the same level of output provided the battery voltage is above the Vf of the LED, and still within the range of the regulator.

It's the boost style regulated flashlights designed for use with power sources at or below 3V (like single AA and single CR123 lights) that end up brighter on a 3.7V cell as a result of the driver not being able to hold back the higher voltage, but rather, allowing the battery to direct drive the LED.

So in some cases, more voltage does produce more light, but usually it is forcing the flashlight to operate out of it's design range.

Eric

 

[laur]

Thanks for all the well thought out technical explanations.

I now understand why some lights produce more light as the voltage increases and some do not (Did not realize before that the electronics played a role in lumen output).

Special thanks to mdocod for explaining it so the layman could understand.

laur

 

[yellow]

one point has not been mentionned:

changing the number of cells most possibly leads to damage of driver or led.

f.e. that "example" of using an 14500 instead of the normal batt --> in most cases that did give much brighter light output, but within very short time ed else the driver, the led or both.
Dont change anything when not knowing what u do.