Thanks. The L60 series cabs all have a standard 60amp alternator, or an optional high output 90amp (?) alternator.
Mine is the standard 60amp, and I've had no issues with charging with the (4) 55w cab lights on. It does tax the alternator when I run all of the lights and the rear window defroster at the same time.
I also replaced all other incandescent bulbs with LEDs (except the corner lights that I never use) and trimmed 11 amps off the total load.
My numbers:
OEM lighting + (4) 55w cab lights = 34 amps
LED lighting + (4) 55w cab lights = 23 amps
IF 55w LEDs actually USE 55W, that would equate to about 4 amps (each). I have read that these watt numbers may indicate equivalent to incandescent watts and are generally lower in actual power consumption. I don't know if that's true, and I didn't bother trying to actually measure.