Had one of the bulbs in my heating /AC panel blow and need replacement. The bulb are small incandescent twist lock type bulbs, length of the bulb is about 4mm. I had found some LED replacement bulbs at superbrightleds.com that are the perfect fit. Takes a few minutes to remove the panel and then the controls to change out the bulbs but it make a good change for the visibility of the controls.
Here is a link to the bulbs I used....
https://www.superbrightleds.com/more...panel-led/221/
Threaded Mode