I was wondering what kind of wire guage you folks use for on-set lighting. Regular run-of-the-mill Wal-Mart consumer wiring, or heavier 10 or 12 guage 'industrial' strength wire (Home Depot, etc... $40+) ?

Heavy until I cannot stand to carry it anymore.

2 reasons:

1. Larger wire means less IR drop voltage) in the extension cord. A heavy draw of current can really drop some voltage in an undersized extension cord.

2. The industrial extension cords are usually built much better with better components, thicker insulation, etc.

Also depends on if you are using a seperate cord for each light or one cord to a multi tap and plugging in several lights. In the first case, unless you're running more than 50 ft or so OR more than 1K watts, you're probably ok with the less expensive smaller gauge cords. On the other hand, in case two, you really need to add the wattage of all the lights you'll be using, divide it by the voltage (120 in US) to get the amps you'll be drawing. Then ensure that the cord you are using can handle that much current. Example: 1K + 600 +500 Watt lights = 2100 watts. Divided by 120 = 17.5 Amps. That would require a fairly heavy gage cord (and might blow a 15 amp circuit breaker too!)

Here is a link for a PDF file for extension cord voltage drops. This will graphically show the neophyte exactly what effect the length , guage and current draw will have on the voltage at the business of the cord. Bigger is better, but overdoing it is a waste of money and the heavier wiring is toughe to handle.

http://home.mchsi.com/~gweidner/extension-cord-chart.pdf

As an example the first box tell us that a 10 amp load at 120 volts will drop 1 volt in 10 feet and 10 volts in 100 feet. 10% drop is allowable so long as you have a decent voltage at the receptacle. If it's listed it's legal.

Print the list out and keep it in your camera bag.

Here is an interesting program for anyone with a palm pilot. Enter the amp draw and the distance and it tells you what size cord is required.
http://www.freewarepalm.com/calculator/extensioncord.shtml

While I haven't checked the effect on video, I seem to remember that a change of just a few volts made a big difference in light output in my enlarger. So much so that I had a regulated PS for it.

Anyone played with lamp voltage on say a 500 watt lamp to see what effect a drop of 1, 5, or 10 volts would have? Interesting to see what the color temperature changes would be. Anyone have a color temp meter?

If I recall, a 10% drop in voltage equals around 150 deg K drop in colour temp. ( It's close to that at any rate)

Color Temp. drops with line voltage and the aging of the bulb itself. So, if you're white balancing to the lights it shouldn't effect much. What the significance is that your 650 watt light isn't really putting out 650 watts after a couple of hundred feet.

Not necessarily a non-problem.

One light on a long extension cord and another on no extension could make a noticable difference for some people. Like, say illuminating both sides of a face (or white block) with separate lights.

Certainly not going to concern me for most work but if I were shooting something that had to be as good as possible, then I'd be concerned enought to test before I shot it for keeps.

It's a good reason to evaluate the scene with a calibrated monitor or waveform/vectorscope. Most people here don't use color meters. The aging of the bulb will cause more problems (color wise) than long runs for most users. The color of an old bulb will be different if you use a long cord or not.

I could only see the difference if I took a reading off a gray card and then looked at it with a vectorscope. Maybe.

I'd really have to be able to splt-screen two scenes together to tell the relative color temp. Except for gross differences.

I'll have to try to read close but not equal color temps with my DSR-300. When I white balance it, it gives me the color temperature. I have, in the past, only checked to see if it is near what I think it should be.

Yea, aged lamps do change in color temperature. I've never looked at the change due to age in a halogen or HMI. Have you any info on them?