Beginner's primer

[MrNaz]

I would like to start work on making my own custom scuba dive light, but I need some info on the ins and out of working with LEDs. I have a basic understanding of circuits from high school, but would like to read a primer on the various things that I will need to know before I can get to work.

I have a Princeton Tec Miniwave that I simply desoldered the old emitters and put in 4 x SSC P4 into, and have gotten a noticeable, but not as large as expected, jump in output. I think I am underdriving them, or perhaps have them running at a sub-optimal efficiency. Perhaps I need a higher current, or higher voltage, I don't know which, so I don't know how to maximise the output. The miniwave has 4x C batteries in series powering 3 x P4 emitters in parallel, with just a resistor in series. Perhaps changing the resistor would increase output? I don't know what the resistor is, the light is not on hand.

Any pointers to good articles? How about tips on my Miniwave modification?

 

[yellow]

sounds like a direct-driven light,
You wont get too much good sayings for them here, because it is an easy but not so good setup.

By getting a smaller resitor value, the current will increase, but directs have one prime problem:
at the beginning, when the batts are full, the current has to be restricted (by the "large" resistor).
Thus, as the batts get lower in voltage, the current to the led reduces.
Unfortunately the ratio the output reduces is much more than the reduction in current, thats how led work.

Example:
(pics I once stole from flashlightreviews).
the red line is the output.
regulated lights (upper) keep the light stable till the battery voltage is too low
direct-drive lights (lower) start bright, but reduce output considerably at the beginning, with that reduction lowering but being kept
- the light "fades away", while regulated ones will be more-or-less stable and suddenly drop to emergency output, or quit totally

PS: a 4 cell light possibly wont be as bad as the three celled lights here, but ...