Boeing 737 classic aircraft use cockpit panels which are backlighted by incandescent bulbs. They are driven by 5V (not 28V like all other bulbs, so please don’t burn them, it happened to me). The bulbs are connected in parallel, they are directly soldered onto a PCB and fit through holes into the semi-transparent backplate.
Unfortunately, after 30+ years those incandescent bulbs are not that effective any more and the backlight is rather dim. They also draw quite some power as you can imagine (more than 1A per lightplate).
I have now fitted 12V LED strips (using 120 LED’s per meter) in pairs of 3 LED’s to the lightplate and thus had to drill another two holes per bulb hole:
The result is fascinating. A more even distributed backlighting which is much brighter and is dimmable by a PWM mosfet driver from a common microcontroller PWM capable GPIO output. The current drawn by the lightplate went down from 1 A to 0.2 A:
You can for instance use the Joy-IT COM-MOSFET driver to dim the backlight from software. It accepts 3.3V or 5.0V logic inputs.
Another option is to use the existing light bulb places and solder individual LED’s to these places. In the next image you see a light plate with 5V light bulbs from the IRS Display panel found in the aft overhead section.
The 7 light bulbs consume a ton of power: more than 380 mA! And they get hot:
The key was to modify the parallel print layout so that always 3 white LED’s form a serial circuit and they can be easily connected to 12 V with a resistor:
A bit of drilling and cutting was needed, and I decided to only use 6 LED’s. The luminosity is great with the LED’s, see here:
And the comparison between the old and new lighting clearly shows that we have the same or better background lighting with LEDs with a current of only around 38 mA, so 10 times less!
