Change to 12 Volt Low Energy Lamps.
This will reduce your power consumption by between 50% and 80% for the equivalent light output.
Eg. a 10 Watt Halogen lamp produces the same light output as a 20 Watt standard bulb but uses about half the power and a 7 Watt compact fluorescent lamp gives the same light as a 40 Watt standard bulb but consumes only 20% of the power. Both have standard bayonet fittings and can therefore be used in "off the shelf Table Lamps directly on 12 Volts simply by replacing the mains plug with a 12 Volt type.

LED LAMPS: If stated that the lamp has a built-in voltage regulator the maximum input voltage is 15 volts DC, otherwise the maximum input voltage is 12 volts DC, over voltage can damage these lamps and void the guarantee.