What do Philips’ CSLS controllers actually do? I know they help keep the colour temperature constant by controlling lamp voltage but how do they do it? How can a controller determine the wear of a lamp and give it the right voltage for a right colour temperature?

Thanks for your question. After doing some research, Philips CSLS controllers (like the CSLS 50 or 100) are specialized electronic control units primarily paired with SDW-T (White SON) high-intensity discharge lamps. They stabilize lamp power and voltage to prevent the significant color shifts and warm-up issues common with high-pressure sodium lighting.

What do Philips’ CSLS controllers actually do? I know they help keep the colour temperature constant by controlling lamp voltage but how do they do it? How can a controller determine the wear of a lamp and give it the right voltage for a right colour temperature?

CSLS controller has a TRIAC in series with a choke/lamp to stabilize lamp current using a feedback from a current sensing resistor. In a way like a regular TRIAC phase dimmer works, by chopping about 1/10 of line frequency period. Additionally, it compensates lamp current for lamp aging, to keep stable arctube temperature as it gradually blackens. For this a regulator uses not only a current, but a sum of momentary lamp voltage plus momentary lamp current in the feedback loop.

See some reverse engineered info and oscillograms here: https://www.lighting-gallery.net/gallery/thumbnails.php?album=7723

Very interesting, thanks RRK! That thread is a goldmine