Never heard of LED Christmas lights?

LED stands for light-emitting-diode

Wiki says:

LEDs are widely used as indicator lights on electronic devices and increasingly in higher power applications such as flashlights and area lighting. An LED is usually a small area (less than 1 mm2) light source, often with optics added to the chip to shape its radiation pattern and assist in reflection.[2][3] The color of the emitted light depends on the composition and condition of the semiconducting material used, and can be infrared, visible, or ultraviolet. Besides lighting, interesting applications include using UV-LEDs for sterilization of water and disinfection of devices,[4] and as a grow light to enhance photosynthesis in plants.

Have a "green" holiday: save money and the environment says:

Many local hardware stores carry LED Christmas lights, which are up to 90% more efficient than traditional incandescent Christmas light sets. They cost more up front-- but they'll save you money in the long run.

The U.S. Department of Energy says if all conventional incandescent Christmas lights in the country were switched with LEDs, we could save enough energy to power 200,000 homes for a year.

"They last a lot longer so you don't need to get rid of them as soon. And they're a lot smaller so there's no mercury in them like fluorescent light bulbs would have in them," said Jim Wicke from Ace Hardware Store.

LED lights are also safer than conventional Christmas lights because they produce much less heat.

"You don't have to worry about it leaning against something that's combustible or anything like that," Wicke said.

Check your local hardware store for some great holiday sales for LED Christmas Lights (for both indoor and outdoor).