It will power two 400 watt lamps.
A 400 watt Mercury vapor light bulb produces roughly 23,000 lumens. In comparison to a 400 watt metal haloid and or high-pressure sodium, not as good. Metal haliod and high-pressure sodium produces 30,000 lumens.
400 watt metal halide fixtures can be purchased at various sites on the internet. Some sites that you may want to try out include the following: Amazon and Home Depot.
Yes U can just make sure they are the same size (watts) and base configuration (R59) or so.
Yes, provided the bulb types are compatible with the 400 watt ballast.
1 Joule is 1 Watt-Second. 1 Watt Hour is 3600 Watt-Second or 3600 Joules. 400 Watt-Hours is 1440000 Joules.
Four 100 watt light bulbs or anything else that sums to 400 watts.
Per hour the answer is 400 watt-hours or 0.4 kW-hours (or units).
It will, but only 1.75 decibels louder. The smallest change in loudness that most people can detect is 1 decibel, so the difference between 400 and 600 watts would be barely noticeable.
The solar component for a 10 watt system can be had for under $400 USD.
800 watt should be fine
400 times 12.5% equals 50.