In LED Versus Incandescent Bulbs (An Update), I mentioned that I replaced the incandescent bulbs in my kitchen with LED bulbs:
- Former: BR-30 soft white bulb, 65 W, 635 lumens, 2700K
- New: Philips SlimStyle 65W-equivalent BR-30 soft white bulb, 9.5 W, 650 lumens, 2700 K
Over the following year after switching to the LED bulbs, I felt as if my electricity bills were slightly lower. To verify, I pulled my electricity bills and computed the total energy cost for the year before versus the year after. I found I actually saved $120 in electricity costs. I decided to perform some match to see if the amount of savings was directly attributable to the lower energy consumption of the LED bulbs in the kitchen.
If your home is like mine, the kitchen is the center of activity in the home. In my kitchen I have five bulbs that burn, on average, about eight hours per day – two hours in the morning, and six in the evening, roughly. The power consumption for one of the LED bulbs I mentioned earlier is 55.5 W less than the equivalent incandescent it replaced. Multiply by five bulbs yields 277.5 W less to light the kitchen with the LED bulbs than with the incandescent bulbs.
To figure out annual energy usage and cost per year, I’ll perform some simple math. First, I’ll convert 277.5 W into kilowatts by dividing it by 1000, and then calculate the energy usage in kilowatt-hours per year:
0.2775 kW * 8 hours/day * 365 days/year = 810 kW-hr/year
At 12 cents per kilowatt-hour rate for electricity in my area, the result is an annual net savings of about $97:
810 kW-hr/year * $0.12/kW-hr = $97/year
That’s in the ballpark of the $120 in savings I actually saw.
The bottom line is that the decrease in my electricity bills is highly correlated to the switch from incandescent bulbs to LED bulbs in my kitchen. It gives me a thought to identify other opportunities to save elsewhere in the house. At least from a lighting standpoint, I know I have to be careful to identify higher-usage lights to be able to recoup the costs of the LED bulbs. But there are other electricity-consuming devices in the house….
Clearly, variations in usage of other electricity-consuming devices will pollute the answer. In Houston we rely upon air conditioning to bear the warmer months, which is often a big consumer of electricity and causes large seasonal variations in total energy cost from month to month. By taking the annual average and assuming that the usage of electricity is the same from year to year, it should negate these seasonal effects.