The only way you are going to get the various mis-matched LEDs to match (approximately) in brightness, and a brightness that is pleasing and won't alert the photon police, is to tune them.

I don't know what kind of access you have to electronic components, but I would start with a full-sized pot (as opposed to a small trimpot) of 5K or 10K, and a fixed resistor of 470 to 1 K ohms. You already have the LEDs mounted, which is good because you will be evaluating them with the real background. Connect to one LED, adjust for the maximum (non-death) brightness you want, disconnect, measure the pot, write down the total resistance, move on to the next one. You will end up with a table of resistor values.

With that list and a table of standard 5% resistor values, you should be able to adjust the desired values up or down a little to reduce the number of different resistor values. With those values, you've set the max brightness for all LEDs. If some of the LEDs are to be adjustable, a pot goes in series with the resistance you've determined. A pot value of 5x to 10x the fixed value should work, but this part is very-variable; I don't think matching the minimum brightness is as important as matching the max's.

ak

I did buy a selection of resistors and a multi-meter so will give this a go - will hopefully mean I’ll get a bit better at soldering by the end of it!

 

He mentioned grandson so, if he did die, it was many years later (and cruel to bring up here). Keep up.

No, he is still alive and well and the two grandsons are now at an age where they have other interests.
AND, BY THE WAY!!! That is a terrible question to pose. Totally out of place in all regards. Offensive, even!!

 

No, he is still alive and well and the two grandsons are now at an age where they have other interests.
AND, BY THE WAY!!! That is a terrible question to pose. Totally out of place in all regards. Offensive, even!!

Copy @AnalogKid, he asked the stupid question.