[Gooner78]

A post I read from a Phillips rep said its ok to run a 400w MY lamp on a 400w hps ballast. It seeminly runs fine,ballast is cooler than running hps.But the lamp seens very hot.It blistered the lampshade paint an my ir thermometer reads 100'celsius!! on the metal above lamo

[Big Sur]

Hint: do not believe everything that you read on the internet!

[Phaeton]

The HPS igniter puts a stronger voltage surge to the arc tube than needed for MH, the bulb should light right up immediately if not sooner. The larger capacitor allows more current flow as well to compensate for HPS bulbs losing resistance and sucking more power as they age, this causes the MH to age faster and run hotter because the resistance does not match.

The MH bulb will run on HPS ballast.
Bulb life will be shorter.
Spectrum will differ slightly from advertised.
Chance of arc tube rupture, while low, is greater when running hot.

Been there and done that, but not long term.

[Gooner78]

Thanks mate. Think I'm gonna get an MH ballast. I was under the impression the only diff was that the ballast has an ignitor as well as the bulb ...i guess what Big sur said is true lol

[Gooner78]

Also the mh lamp i notice looks like the little glass tube in the middle has brown burnt sulphery looking poweer on one side of the glass. The bottom side ..Normal??

[Phaeton]

Originally Posted by Gooner78

Also the mh lamp i notice looks like the little glass tube in the middle has brown burnt sulphery looking poweer on one side of the glass. The bottom side ..Normal??

Those are salts used for the arc. The voltage surge ionizes the salts which then emit photons as they turn to plasma. When the lamp is turned off the gasses condense back to salts as they cool.
As the lamp ages the lighter molecules out gas first, leaving more visible metals in the tube.

Ceramic Metal Halide refers to the arc tube. The salts used for deep reds are highly corrosive and eat right through a quartz tube. A ceramic tube (similar to that used for sodium in HPS) is much more chemically resistant, giving an equivalent life with the improved spectrum.

[Big Sur]

Originally Posted by Gooner78

Thanks mate. Think I'm gonna get an MH ballast. I was under the impression the only diff was that the ballast has an ignitor as well as the bulb ...i guess what Big sur said is true lol

You can get a switchable MH/HPS ballast. They are not that much more. I have one myself (Sunlight Supply), and it works great. The rest that I have are dedicated MH ballasts. Though I rarely use my Sodium bulb. MH works in both veg and flower mode, and I use my indoor setup mainly for veg grow and re-vegging.