OK, I hope we have some knowledge here on the operation of multi vapor lamps, their respective ballasts and operating wattage compatibility. I have a "light tower" that I am attempting to put back into service. It is older, and the repair parts I need are obsolete and NLA, even from the manufacturer (Magnum). The original equipment is 4 1000 watt (mh1000/U) lamps. The owner of the tower first wanted to convert to LED, but that conversion is prohibitively expensive. Runs about $1,700 per fixture (X4), so I am going another direction. He also has available some indoor (suitable for wet locations) complete fixtures that were taken down elsewhere. However, they are only 400 watt fixtures with all plastic housings and lenses. They are physically much larger than the aluminum original reflectors. I have serious doubts that 1600 watts will be satisfactory on the tower, which is intended to extend to about 30 feet vertically. That would be replacing 4,000 watts of light. So, it was suggested that I simply do some fancy swapping and use the plastic housings and lenses on the 1,000 watt lamp assemblies. The 400 watt fixtures were meant for stationary installations, and have the ballasts built into a cast aluminum housing, making the whole fixture weigh about 10x what the original does. So the design weight capacity of the mast would definitely be out of a safe range, IMO. I could relocate the ballasts to where the present ballasts are, inside the cabinet of the trailer. That could turn into a lot of hassle and may not be all that easy. Not my first choice. All in all, my gut tells me that the plastic parts from the 400 watt fixtures, while I could build adapters and mount to the 1,000 watt receptacles, would not hold up to the 1,000 watt lamps due to the heat generated. Plus they do not function as reflectors. Plus they are much larger and would present a greater wind load, a danger when elevated. And as this is a trailer, I'm quite certain the vibration would crack them and eventually they would be lost while transporting. That's the story; now my question. I know the ballasts are different for the two different lamps, even though they are the same style and type lamp. What I need to know is what could happen if I run the 400 watt lamps from the ballasts meant to power the 1,000 watt lamps? I am supposing the strike voltage should be less, as the 400 watt lamps have a shorter inner envelope where the vapor and arc actually are. But the strike voltage is only for a short duration. The actual arc voltage should be the same, maybe.....that's part of the question. What I really want to do is get a glass company to cut me some circles of tempered glass that can handle the heat. I can fabricate some clamps to hold it in place. That seems to me to be the best way to get the full 4,000 watts of light out of this tower. I can stay with the aluminum reflectors that were designed to take the heat, reflect the light downward, and tolerate any vibration they may experience. Plus this leaves me out of messing with trying to wrangle the wrong ballasts into the machine. The glass pieces would be about 19" in diameter, so I am thinking 1/4" thick would be acceptable. So what say ye? Any options I am overlooking?