Much of the lighting in older houses use incandescent light bulbs that consume 75 to 100 watts each.
Most indoor incandescent lights use a tungsten filament such that they transform about 90% of the electrical power to heat and have only 2.5% luminous efficiency.
A Compact Flourescent Lamp (CFL) can produce about the same amount of light as a 75 watt incandescent light and consume only 30 to 40 watts. CFL's use a FET switching transistor and coils to generate a high voltage discharge through a mercury gas. A coating inside the bulb converts the mercury's UV light to visible light.
When I use a CFL, I try to use a light with a color temperature of 2,700 K, since it more closely duplicates an incandescent light. If you need a bright bench light, use a 5,000 K or 7000 k light, which generates a bluish white light.
If you break a CFL, take off your rings and jewelry and use gloves for clean-up since mercury can be poisonous.
I use soft gloves to screw in CFL's for that reason.