Every year during the holidays consumers are inundated with warnings about the dangers of purchasing the wrong kind of Christmas tree lights, information on how to hang them properly and proper use of extension cords.

This Christmas season we decided to add something along with a few of the old how-to tips on Christmas lighting. Our new twist concerns a way that you can count on to safely calculate how much lighting you can use no matter what kind you decide on.

When we were kids our parents had outside colored lights that used about 25 watts of electricity per bulb. You can imagine how the electric meter spun when dad would power everything up for the evening.

Now, a 50-foot string of outdoor lights costs less than $10 and uses a total of about seven watts of electricity. All that and they come with their own built-in fuses. When you buy strings of lights make sure to purchase extra bulbs and fuses. Next year your store may offer another manufacturer's product, and those bulbs and fuses probably won't work with yours.

It is important to measure how much lighting is added to an electric circuit. How to measure electricity is the tip that we hope will help you to maintain a safe and nicely lighted home for the holidays.

Amps times volts equal watts. Normal household receptacles are on 110-volt circuits dryers and stoves normally use 220 volts. The fuse on the circuit will tell you how many amps that circuit will carry, usually 15 or 20 amps. Examples:

1) 110 watts times 15 amps equals 1650 watts
2) 110 volts times 20 amps equals 2200 watts

When lights are going to be left on for more than an hour, a safety factor should be used to offset heat build-up. Eighty percent of the total line wattage should be used as the maximum safe line wattage in these situations (for 15-amp circuit: 1650 watts x .80 safety factor = 1320 watts, for 20-amp circuit: 2200 watts x .80 safety factor = 1760 watts).

Once you know our formula the hardest part of the job is over. All that is left is to find out how many watts are being used on the circuit into which you intend to plug your lights. This is important. We mentioned that 1320 watts was a safe limit for a 100-volt 15-amp circuit being used for lighting that is to be on for an hour or more. Using a 1500-watt hair dryer on that same circuit could be a fire-causing decision, even if the lighting is only a few hundred watts.

Identifying all the appliances on a circuit is easy. First, turn on every light fixture in the house, closets, garage, outside, everywhere. Next, turn off all but one breaker in the electric panel. Then, look for the lights that are left on. Also, use a tester in every wall receptacle to see which ones are still on. Don't forget the one in the medicine cabinet and the one behind the toaster. Finally, check appliances such as the refrigerator and range hood. Make a map before you begin and highlight each circuit in a different color. Color code your electric panel to match.

Once you know which items are on which circuits you can calculate the wattage use by reading the information on the appliance or light bulb (TVs are about 95 watts). Add everything and subtract the sum from the wattage allowed, and that is the amount left for other uses.