You DO use the old wire. You must not run new wire and outlets of proper load rating for the job. Doing anything else is dangerous.
No, you must break it down to a 120 volt supply.
240V is much more effecient, and you can put more heaters on a 20 amp circuit than you can a 120V.
If your trying to plug in a 110 Volt lamp into 240 volt outlet the answer is simple. You must buy a step down transformer, or your lamp will burn out.
If the light you refer to is just a plain incandescent lamp, then changing the plug and changing the lamp to a 240 volt lamp should work OK If the light has a ballast (transformer-like winding) of any kind, the voltage rating of the ballast has to match the line coming in. A few ballasts have multiple taps - you may be able to change the internal tap from 120v to 240v you can not convert it. Otherwise connecting a 120v ballast to 240v will damage it quickly.
It will work it you use 240 volt light bulbs.
I think the only sure way is to put a high-impedance volt meter and measure the voltage across live and neutral. Don't forget that it's AC. You could look at the bulbs in the lighting to see if the say 120v or 240v.
wire in the us is available in 300v or 600v ratings so 300 volt is good for 120v 240v or 277V 277V is usually only used in lighting
240 watts to 120 volts? Or 240v to 120v? What kind of meter? As in an electrical test meter?
A 240 volt breaker can be removed and replaced with 2 - 120 volt breakers. The existing 240 volt breaker should not be used to supply 2 separate circuits.
If you mean that the lamp is rated for 240 volts then yes, a 120 volt bulb will operate in it if the lamp bases fit. If the 240 volt lamp is operating on 240 volts then no, a 120 volt lamp will not work in the fixture.
ANSWER FOR THE US: The red wire should have the same as the black, which is 120V to ground, or 120V to neutral. Without the neutral, you will have 240V line to line.
You can't. I'm not sure exactly what you're trying to do, but the way it is written is not possible. It seems you might want to use half of a duplex receptacle for 120 and half for 240. This would not be code compliant, nor would it make sense. A plug designed for 240v will not even fit into a 120v receptacle. You need a 240 volt receptacle rated for the amperage you will need. Also, an existing 120v receptacle has nothing to do with your 240v receptacle. For a 240 volt receptacle, you'll need to run 2 new 120v lines (in the same cable). The existing 120v circuit cannot be used here, even if you added another 120v circuit, because when a load uses 240v, both 120v circuits supplying the 240v must be controlled by a common disconnect (a 2 pole breaker designed for 240v circuit). My advice would be to show an electrician what you want done. I'm sure they can tell you how to make that happen.