Ah, I must be overcomplicating things.....

Ive been sucking up information (along with lego components) here for a bit of time now, not long mind you. I think I'm getting the hang of things, then WHAM! I'm smacked in the brain with something else to consider as far as flashlight electronics go. So, I thought I'd ask about building an led flashlight circuit and how the components- led, driver, and others not mentioned- determine how many 3.7v cells can/need to be used to power them. Do multiple LED drop ins need more volts? Amps? ??

I've heard of "driving an led hard". I have absolutely no clue what that means. I'd like to though.

Thanks for your time.

If you have the right driver matched to your LED, the number of cells mainly determines the run time. As an example, if your setup will work with one Li-Ion cell, then two in parallel will essentially double your run time. The same if it takes two cells in series (shorthand is 2S) to operate, then two sets of 2S, or 2P2S (two sets in parallel of two cells each) will do the same.

If your driver is flexible enough, you can also set it up with two cells in series. The increased voltage into the driver will translate into less current being drawn from the cells. If I understand things properly, this setup might not be quite as efficient, but should be close. Again, adding another set of two cells in series paralleled with the first set will double your run time.

As far as 'driving hard', that refers to how much current you are pushing into the LED. Within limits, the more current available to the LED, the more output, up until the LED gets hot enough to either shorten its life significantly, or burn it out. Look at any LED data sheet and you can see the numbers for lumens at various currents, as well as the top end current recommended.