"How efficient are LED strip lights?" I can't answer that question. But I can say they're a lot more efficient than non-LED type lighting. I've seen rope lights that consisted of incandescent bulbs. Incandescent wastes a lot of heat, and therefore from a "Lighting" standpoint they are poor when considering efficiency. LED's DO generate heat. And heat can be a problem for LED's. With increased temperature their forward voltage drops, increasing the current, which increases the wattage (heat). Managing that heat becomes important. Even critical. Since I had a bad experience with a cheap LED strip I'd be more prone to include some sort of heat sinking in the future.

Christmas tree lights used to be incandescent. Probably can still find such. But they are a far greater fire hazard simply due to the amount of heat they can give off. LED's became popular simply because they use less energy. Less energy means less heat and much greater efficiency. Since you ask about efficiency - I'd have to say "They are far more efficient (by about 80% from what I hear) than other forms of lighting. Not withstanding is CFL (Compact Fluorescent Lighting).

 

LED tree lights also are popular because they seem to be much more reliable! At least, some types seem to be much more reliable. The frosty blue-white of some of the first strings was an issue for some folks, but that sems to have been corrected. Our frosty strings were assigned to outside use. They do have problems with rain, however!

 

Blue (almost ultraviolet) LED's on 60Hz, flashing EDIT: 30 60 END EDIT times a second drive my vision nuts! But we're off topic now.

 

Blue (almost ultraviolet) LED's on 60Hz, flashing 30 times a second drive my vision nuts!

The leds will flash with 60 or 120 Hz, depending on single or double rectification.

 

The leds will flash with 60 or 120 Hz, depending on single or double rectification.

OK, yeah, I kind of got that wrong. Cheap ones flash 60 x per sec. And it is hard for me to look at them. Especially when they're bunched together. Hurts my eyes.

 

Adding a filter capacitor greatly reduces the flashing effect.