Does turning on and off a light use more energy than leaving them on?

With lights (especially non-incandesant), probably not, as there is no significant "ramp up" of electricity required to induce function. However, most if not all electrical equipment (including lightbulbs) fails when powered on or off, or when it undergoes any significant state change. If you consider the environmental impact (read: energy use if you wish) of recycling burned out electronics and manufacturing new replacements, the picture changes. When we look up the technology ladder to computers, when CRT's were the screens of choice, you'd see replacements required for monitors every one or two years if they were turned off and on daily, and up to six years or more lifespan if they remained on in screensaver mode (my own experience). When you consider the toxic impact of properly disposing of items such as these, it makes more green sense to leave them on. In summary, with lights, I'd say turn them off. However, the greater the current draw from the item, and the greater the environmental impact of recycling and manufacturing, the more you should consider leaving it on. It's not a simple yes/no, is it? :}