Hi all,
recentely i got a good deal on a 50W SDW lamp, however i don't have the correct equipement to run it.

Does anyone know about compatibility or how SDW controller works?

Thanks in advance!

It is (indirectly) monitoring the arctube temperature and so adopt the power to keep it at designed level. It needs a special regulator on top of the choke ballast, maybe some electronic ballasts may have appeared in the later years, but it is all Philips proprietary, dunno where to find exact description how the control is supposed to work and what should be its parameters. I would guess it was even never made public by Philips.

Other companies designed their "white sodium" lamps differently, some even do not need any active control and suffice with bare choke/ignitor.

Ok, thank you Medved!

The ballast & controller system specific to the N.American 50w SDW-T lamp appears here. Typically these need a specific socket and the capacitor is also required.

There is a detailed description of the controller in the Philips OEM Technical Manual for SDW lamps.

It is basically a device that helps to fine-tune lamp power during mains voltage fluctuations.  Normally when a lamp has fully run up, its voltage is relatively stable.  Mains voltage variations might then cause a small shift in the current supplied by a magnetic ballast, which in turn cause a shift in lamp power.  With that are parallel changes in temperature, light colour and lamp life.

The problem with SDW lamps is that a tiny change in lamp current and temperature also cause a very wide change in arc voltage.  Which further exacerbates the problem.  Small drifts in mains voltage cause huge variations in the colour, efficacy and life.  So much so that no customer would be satisfied with the resulting performance variations.

The purpose of the electronic controller is to help the magnetic ballast better absorb these mains voltage fluctuations, and keep lamp performance stable.

It is harmless to run an SDW lamp on ordinary ballasts, but if the mains voltage is now precisely the same as the rated ballast voltage, the light colour, luminous flux and lamp life might be very different than published.

But running an SDW lamp on an "ordinary" ballast in countries with 120v versus 240v raises additional problems. For the same watt lamps, the SDW lamps for European markets cannot run on the N.American ballasts. In fact they won't even ignite, or if they do, take forever to ignite.

I haven't tried this yet, but I'm guessing that N. American SDW lamps will easily ignite but will be overdriven on European gear of the same watts.

There is a detailed description of the controller in the Philips OEM Technical Manual for SDW lamps.

It is basically a device that helps to fine-tune lamp power during mains voltage fluctuations.  Normally when a lamp has fully run up, its voltage is relatively stable.  Mains voltage variations might then cause a small shift in the current supplied by a magnetic ballast, which in turn cause a shift in lamp power.  With that are parallel changes in temperature, light colour and lamp life.

The problem with SDW lamps is that a tiny change in lamp current and temperature also cause a very wide change in arc voltage.  Which further exacerbates the problem.  Small drifts in mains voltage cause huge variations in the colour, efficacy and life.  So much so that no customer would be satisfied with the resulting performance variations.

The purpose of the electronic controller is to help the magnetic ballast better absorb these mains voltage fluctuations, and keep lamp performance stable.

It is harmless to run an SDW lamp on ordinary ballasts, but if the mains voltage is now precisely the same as the rated ballast voltage, the light colour, luminous flux and lamp life might be very different than published.

Thank you, James!

But running an SDW lamp on an "ordinary" ballast in countries with 120v versus 240v raises additional problems. For the same watt lamps, the SDW lamps for European markets cannot run on the N.American ballasts. In fact they won't even ignite, or if they do, take forever to ignite.

I haven't tried this yet, but I'm guessing that N. American SDW lamps will easily ignite but will be overdriven on European gear of the same watts.

Maybe is due arc voltage?

Yep, I think. Just like normal HPS lamps, lamps between 240 and 120 volt countries are NOT interchangeable for wattages below 250 watts.

Hi, i just tried with 70W MH ballast, seems to work fine, but i'm going to buy a proper ballast.