Hi,
Many thanks for answers (Not allowed to click on any more "helped me" today, sorry guys...).
The Zener I found is/was 1.8V, 50uA Iz (1.71 to 1.89V min and max), but after FvM and Audioguru's much neater suggestions, I have a SOT 1.25V reference that could fit the bill.
Just to explain premise: I have a cheapo headtorch I need to use frequently every day but mostly only for a few seconds at a time, it has one pushbutton so you are forced to cycle through on-flashing-off and I am sick of the "flashing" button press step to get to "off". I sometimes need to see what's rustling in the bushes at night - fox, boar, hateful feral male cat chasing my furry girls, or if it's actually my cats making the noises - the brightness must be blinding the poor little things, so adjustable brightness would be fun to design. Red or green LEDs would be good for that, but white scares away wild animals which is a big plus in my opinion.
I don't have an up/down counter IC. Using a 4017 for only cycling through up and reset is by now something I'm sick of repeating, even though it makes the stepped current level design really easy to implement.
I came up with this idea:
For a typical online supermarket/European penny store style piece of rubbish I wondered how workable the idea is.
I've only been working on this idea and the number-crunching for a few hours over a couple of days, some values are presumably very provisional until the calculator and reality coincide in a workable way, which is why I didn't post the whole schematic.
The source and sink are supposed to charge and discharge C1 by pressing either pushbutton to make a short-duration variable voltage reference for the op amp constant current source so as to adjust LED brightness.
I know it's a stupid and bad (and maybe pointless) circuit, it's my way of learning a bit more (hobbyists, eh...) and using mainly components I do have at home.