I am in need of a 400w Mercry light bulb for one of our work lights on our stage.  Does anybody know the "least" expensive way to find one?

Thanksfor the info.

Is there a main difference?  I mean, if the bulb that I had before was a mercury, do I need to stick with the mercury, or will a haologen bulb work just as well.

The ballasts are different for various lamps (Mercury vapor (blue) or Sodium (yellow) or Metal Halide (normal)).  Halogen lamps do not require a ballast.  Mercury vapor, Metal halide and sodium take several minutes to come to full output while Halogen come on immediately. 

For the most part the ballasted lamps can not be dimmed (much).  The advantage of the ballasted lamps is their efficiency so if you need a lot of light from a fixture and need it on for many hours a day (like a streetlight) and can wait five minutes or so before they reach full brilliance they make sense.  On the other hand, if you need to light a smaller area and just use them a few hours at a time, I would change over to Halogen lamps.  If you are using any of them indoors, make sure the fixture is rated for indoor use.

If I was lighting a warehouse or garage I would consider a ballasted lamp.  For work lights on stage I use 400 watt Halogen lamps.  They may not last as long as ballasted lamps (1,500 hours vs 10,000 hours) but at 3 or 4 hours a day they last long enough and they are available at any hardware store.

I appologise in advance Pauliebonn! For taking your topic on a slight tangent!

I was thinking on the colour aspect of the various types of lamps & their colours, as commented on by Russel & Dougb.

When I was a young bloke of 12 or their about & got to play with different types of bubbles [globes] in theatre. One effect I was impressed with, which I?m attempting to remember, is the Smioloff effect, [unsure of the spelling!] or named something similar? This was used in the Musical ?My Fair Lady? in the Ascot scene. The cast was dressed in black & white costumes, then the sodium lamps were switched on, to give a yellowish hue to the white of the costumes, at the end of the scene - very effective! I was going to use this some 20 years ago for another show - unfortunately it never came about, for various reasons, I can?t remember the details now!

Back on topic, I would tend to go along with the others, & suggest you change out your Mercury lamps for halogen, because of the colour the others put out, especially on the stage work area. Industrially these work because of reasons of costs & maintenance, But I prefer to use either incandescent or halogen, when on the stage, as their is no hue changes of light, other than what would be applied during ?show mode? & enhanced by taking out the colours of the spectrum not required with gels.

I hope this may help - if you were contemplating replacement of the work lights?