Help -Educate- me on a few "custom" light ideas

[Digital]

I've been reading the forums constantly for weeks and have a fairly decent understanding of the idea behind what makes a good throw light. But I think I might be missing something.
It seems that everyone who makes a very high powered searchlight does so with some type of custom setup that costs them zillions of dollars. Between the bulbs, ballasts, hosts, custom lenses, batteries, blah blah they spend a fortune.
I was searching around ebay for a while and came across some lights like these: http://www.ebay.com/itm/400-Watt-Met...item5886d8e23b
Is there any special reason why you couldn't modify something like this to be a throwing monster on the cheap? Or am I missing some large part of the puzzle?

[AnAppleSnail]

Well, you start with a 400W metal halide bulb. Have you seen them up close? The arc chamber in them is about the size of a bit grape, or the last joint on your thumb. Being an arc lamp, the peak brightness is at each end of this cavernous space. To make mega throw, you need a high Optic to Source ratio. If you have a brilliant sand grain-sized source and a palm-sized reflector (Stanley HID), you can get about the same throw as a brilliant pea-sized arc lamp and a face-sized reflector, and so on. So with a grape-sized arc, you'll need a big reflector.

Second, power. If I use a portable power source, it will be DC somewhere. 400W / 12V = 33.3A. That's SOME battery. And jumper-cable-sized wires. Next you have a ballast. The ballasts for these lamps are quite expensive, being high-power, long-life devices. And they run on 220VAC in much of the US. A low-voltage DCC ballast for a 400W beast would be quite the custom high-power gadget.

Edit: I see that this one claims to run on 120 VAC.

So a build based on that, for throw, would consist of:

A backpack with two or more deep-cycle batteries (100 Ah each at 13V)
An inverter running 4A at 120 VAC
The metal-halide 220VAC ballast in a handheld unit. These are about the size of a toaster and quite heavy.
The reflector, probably traffic-barrel-sized for throw

I think that'd be a fortune, even if you went the DIY-reflector route some of the spotlight nuts have gone! How about you?

Edit also:

6) What brand are these light fixtures? We have these lights custom manufactured and we do not stamp a brand name onto them. The quality is superb!
7) What color of light do these put out? This is a metal halide light which puts off a white colored light.

Those are evasive answers.

[Digital]

So assuming I didn't mind having this as a backyard toy I would just need to get a bigger reflector? 16" isn't enough?

[AnAppleSnail]

So assuming I didn't mind having this as a backyard toy I would just need to get a bigger reflector? 16" isn't enough?

For backyard fun, a quality extension cord could work. The reflector that comes with it spreads the light out for use on a factory floor. I do not know where you would find an adequate reflector to focus a decent beam, though. Custom reflectors are pricey! These lamps are picky about start/shutdown times, per their manual.