Keeping the Christmas lights on will cost you a little less this year.

Residential electricity rates fell 11 percent on Oahu this month compared with December 2011. The typical bill on Oahu dropped to its lowest level since the spring of 2011.

Hawaiian Electric Co. said a typical 600-kilowatt-hour bill for Oahu residential customers this month is $195.38, down from $219.03 a year ago. The typical December bill was $4.80 less than November’s $200.18 bill and was the lowest since May 2011 when the typical bill was $188.88.

The effective rate for electricity on Oahu in December is 31.1 cents a kilowatt-hour, down from 31.9 cents a kilowatt-hour last month. Electric rates also fell in November and October.

Still, Hawaii has the highest electrical rates in the nation. The statewide average of 37.07 cents a kilowatt-hour in September was more than triple the national average of 12.3 cents a kilowatt-hour, according to the most recent numbers available from the U.S. Energy Information Administration. Idaho, where hydroelectric power supplies 80 percent of the state’s electricity needs, had the lowest average rate at 8.1 cents a kilowatt-hour.

Neighbor islands also reported a drop in electric rates.

» Maui Electric Co. customers saw rates fall to 39.5 cents per kilowatt-hour this month from 39.6 cents in November. The typical Maui bill fell by $3.18 to $218.12.

» Hawaii island residential rates fell to 38.7 cents a kilowatt-hour from last month’s 39 cents. The typical bill fell by $2.03 to $242.46.

» On Kauai the rate fell to 42.6 cents per kilowatt-hour, down from the 43.9 cents per kilowatt-hour charged last month by the Kauai Island Utility Cooperative.

The state’s two electric utilities, HECO and Kauai Island Utility Cooperative, adjust their rates monthly largely to reflect changes in fuel costs. The utilities generate 75 percent of their electricity from petroleum, making rates sensitive to volatility in oil prices.