The end-of-year holidays are all about tradition, but we wanted to see if a newcomer (LED lighting) to the seasonal-decorating game could give the old standby (incandescent) a run for its money. We compared LED and incandescent bulbs in mini, C7, and C9 sizes to determine how much it cost to light 50 feet of strings for 300 hours. We also exposed the bulbs to moisture, hot and cold temperatures, and UV light, and had an independent lab measure brightness. Here are the results of our holiday light head-to-head:

Price. The LEDs cost more per string than the incandescents: $16 for the C7 and $20 for the C9 compared with $10 (C7) and $11 (C9) for each incandescent string. What’s more, each string of C7 and C9 LEDs was 16.7 feet long compared with 25 feet long for each incandescent string. As a result, it cost more to wrap a tree with 50 feet of C7 ($48) or C9 ($60) LEDs than with C7 ($20) and C9 incandescents ($22). (The mini-LED strings we tested were as long as the mini-incandescent strings—25 feet—but cost $3 more apiece.) Note that the 50-foot runs of C7 and C9 LED and incandescent lights had the same number of bulbs: 150.

Energy use and costs. LEDs used 1 to 3 kilowatt-hours of energy while the incandescents used 2 to 105 kWh, saving $1 to $11.

Durability. All LED bulbs were still working even after 4,000-plus hours, while each string of incandescents had one or more bulbs burn out before 2,000 hours. The LED bulbs we bought were also plastic and therefore less likely to break than the glass incandescents.

Brightness. The C9 and C7 incandescents were five to six times brighter than the LEDs, though the mini-incandescents were slightly dimmer than the mini-LEDs.

LEDs are better for the environment; run much cooler, reducing fire risk; should last longer; and could save you money. But it's apt to take more than one holiday season for the savings to kick in, and you might not realize any savings if payback takes more than three 90-day seasons: As a rule, you shouldn't use decorative lights longer than that.

Safety information: Christmas trees are involved in about 300 fires each year that result in 14 deaths. No matter which type of holiday lighting you use, follow our safety advice:
• Make sure the wire for the lights you buy has a holographic "UL Listed" tag.
• Discard any light strings with broken sockets, frayed or bare wires, or loose connections.
• Plug no more than three strings of lights into a single extension cord.
• Turn off your holiday lights when you leave home or go to bed.

For more information on holiday lights, watch our video report.