Adding a strip of white LEDs under the X stage helps shed some light on events atop the M2’s build platform; this was very nearly the first improvement after getting the printer, but somehow I’ve never written down where that nice white glow comes from.
This view shows the strip from below, looking up from the -Y direction in front of the stage:
I originally screwed the wires into the terminals from the hulking 12 V Dell laptop brick for the platform heater, but then I had to unscrew the wires whenever I moved the M2 and I didn’t like sharing the connectors with those huge conductors. Now the LEDs are in parallel with the extruder fan (which runs continuously), sharing the FAN1 screw terminals inside the electronics case.
The M2 firmware uses PWM to cut the 19.5 V supply from a much smaller laptop brick down to roughly 12 V RMS for the fans, but that isn’t such a Good Thing for LEDs. The strip has 120 Ω resistors that drop about 2.4 V at 20 mA from a 12 V supply, leaving 9.6 V for the LEDs (at about 3.2 V each). Running from 19.5 V means the resistors will see about 9.5 V and pass nearly 80 mA, four times the nominal rating, during each PWM pulse.
Based on those measurements, the light output doesn’t go up by nearly a factor of four during each pulse.
I plan to add a 12 V supply to the LinuxCNC box, probably by recycling the 12 V brick from the M2, which will get the LED current back down to a reasonable level. With any luck, they’ll survive this mistreatment and not carry a grudge.
You could, of course, just power the LEDs from a separate 12 V wall wart, but that adds Yet Another Thing when I carry the M2 to demos.
The Smell of Molten Projects in the Morning 
Hmm, you’re not using RBG strips so you could use different colors to show printer status? [grin–spoken by the guy who doesn’t have to do the work…]
Believe it or not, there’s support for RGB “mood lighting” built into some 3D printer firmware; maybe it’s for the Makerbot Replicator series. I’m too fuddy-duddy for that, though…
They likely will carry a grudge, in the way that LEDs do, by being a little dimmer than they used to be, and eventually one will just stop working, leaving a missing tooth look in that string. I doubt either of these is a big deal to you.
The gradual dimness, yeah, I can live with that, but three adjacent LEDs would go out at once and that would be ug-u-ly…
The strip doesn’t project quite enough light toward the extruder head and nozzle, so I may have to gimmick up something better when I add the video camera. The gotcha is that the extruder hits the home switch about 5 mm before it hits the upright around the Z axis rods and leadscrew, so there’s no room in the obvious location. Drat!
I’ve done exactly the same thing to my M2 (red LED strip, the flexible ones)… at the price point, if I get a couple of years out of the (gradually dimming) LEDs I’ll be happy. It looks really nice, and makes it so much easier to see whether I’m getting good ‘squishing’ on the first layer.
Given that human eyeballs doesn’t notice much difference until the light’s at half brightness, I think we’re good for a loooong time…