I had some spare time at work, and we don't have an easy to use neon spectral lamp - only one with bare connections you gotta hook up to a multi-kV power supply.

So i decided to pop the cap off a LED lamp, lever out the LED board (which i kept to show the audience what is actually inside a LED lamp), etch a little circuit board that pops right into the place of the old one (keep an eye on isolation distances) and populate it with 5 strings of 2 neon lamps in series with a 82k resistor.
This gives us a current of 0,73mA per lamp.

It works beautifully, but as expected it is a bit dim. I might make another one but with a 2,5mA lamp current. That will dramatically reduce life span but since i can etch and populate a board in maybe 2 hours time in total, that is acceptable.

Side note: i make boards in-house. Getting them made in China is of much higher quality than i could ever do in house, but i am impatient and want my boards the same day lol. Also the trend of import tariffs is also gonna hit us in a month's time, so boards from china will get a 2 euro tariff (fine, it's just 2 euro and it goes into the european tax pot) with 10 euro of handling fees from the carrier (NOT fine, goes into private hands and FFS, 10 euro for allowing me to pay 2 euro? Get shafted, PostNL).

Very very cool! I did a similar thing with 7 of them and I used a sheet of plastic rather than a PCB but it did work! Like you say there isn't much light emitted by these but it is cool to see. It's long since been disassembled so I can't take a picture of it but maybe that's for the better since mine was made very very cruddily.

Sure your ballast resistors (crammed to the inside of the board) get enough cooling? You are designing a compact lamp after all, and are responsible for thermal mode

Yes, if i run it for a while, then rapidly take it out of the fixture and pop the cover off, my highly calibrated finger thermometer says the temperature remains at or below 60 degrees C. If there wouldn't be mains voltage in there, i could just about continuously hold my finger onto the components. It runs cooler than the LED lamp did before the conversion.
Just out of an abundance of caution i also drilled some small holes right on top and around the lamps themselves.

The resistors dissipate considerably less power than normal because i run 2 lamps in series. I have a whole bunch of them including the resistors from the store, but a single lamp with resistor at 1mA gets considerably hotter, to the degree that i have to redesign a tube shaped lamp i made with 20 of them in there.


I do think re-making this with 20 lamps (or tripling the current and accepting faster wear of the neons) will make me run into thermal issues. I'm gonna dig through the recycle bins and see if i can find a large globe shaped one for a bigger version, where only the resistors are on the board itself and the indicator lights on their own (shrink tube isolated) legs. Just ordered 200 of them before the tariffs kick in, might as well...