 Common is a set of 60 (2 volts per bulb), but white LED sets use two circuits of 30 (4 volts per bulb).Multicolor sets may have special wiring, because red and yellow require less voltage than the newer blue-based ones (blue, emerald green and fluorescent white), but typically come in sets with a multiple of 35.Battery-powered sets typically come in 10 or 12, and can use standard 2.5 to 3.5-volt bulbs because they run two batteries, totaling three volts or less.