Have you ever wondered how much it costs you to keep a light on? Is it really worth switching to compact fluorescent lamps (CFLs) or LEDs? To find out, all you need to know is the wattage of the bulb and the cost of electricity in your home. By replacing an old incandescent light bulb with more energy efficient alternatives, you can save a few euros in the first year and even more money in the long run.
Steps
Part 1 of 2: Kilowatt and Kilowatt hour
Step 1. Find out the wattage of the bulb
You will often find this value printed directly on the bulb, followed by a W. If not, check the packaging. Watt is the unit of measurement of power, i.e. the energy used by the light bulb in one second.
Ignore phrases like "100 watt equivalent" used to compare the brightness of two lamps. Find out the actual number of watts absorbed by the bulb
Step 2. Divide the number by a thousand
This way you will get the power absorbed by the bulb in kilowatts. To divide by a thousand, just move the comma three digits to the left.
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Example 1:
a typical incandescent light bulb draws 60 watts of power, i.e. 60/1000 = 0.06 kW.
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Example 2:
a typical fluorescent light bulb consumes 15 watts, or 15/1000 = 0, 015 kW. This model draws about a quarter of the power compared to the incandescent one.
Step 3. Estimate the number of hours the light bulb stays on in a month
To calculate the value of your bill, you need to know how long you use the light bulb. Assuming you get your electricity bill every month, count the hours the light bulb stays on in 30 days.
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Example 1:
your 0.06 kW light bulb stays on for 6 hours a day, every day. In thirty days, the total equates to (30 days per month * 6 hours per day) 180 hours per month.
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Example 2:
your 0, 015 kW fluorescent bulb stays on for 3 hours a day, three days a week. In a month, the hours of use are approximately (3 hours a day * 3 days a week * 4 weeks a month) 28.
Step 4. Multiply the kilowatts consumed by the number of hours
The electricity company that supplies you with energy charges you for every "kilowatt hour" (kWh), which is every kilowatt of power used for one hour. To find out how many kilowatt hours your light bulb consumes in a month, multiply the consumption in kilowatts by the number of hours it stays on.
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Example 1:
the incandescent bulb uses 0.06 kW of power and stays on for 180 hours per month. Its power consumption equates to (0.06 kW * 180 hours per month) 10.8 kilowatt hours per month.
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Example 2:
the fluorescent bulb uses 0, 015 kW and is on for 28 hours per month. Its power consumption is equivalent to (0, 015 kW * 28 hours per month) 0, 42 kilowatt hours per month.
Part 2 of 2: Calculate the Costs
Step 1. Calculate the cost of using the light bulb
Check your bill for the cost of each kilowatt hour of electricity (the average cost per kWh is € 0.20 in Europe and $ 0.12 in the US). Multiply this value by the number of kWh consumed by the light bulb in a month to estimate how much the energy absorbed by it costs you.
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Example 1:
your electricity company charges you 20 euro cents per kWh, or € 0.25. The incandescent light bulb consumes 10, 8 kWh per month, so it costs you (0, 2 € / kWh * 10, 8 kWh per month) 2, 16 € per month.
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Example 2:
if the cost of energy remains unchanged, the fluorescent lamp costs you (0, 2 € / kWh * 0, 42 kWh per month) 0, 084 € per month, or about 8 cents.
Step 2. Save on your electricity bill
Light bulbs make up about 5% of the electricity costs in our homes. While other energy saving methods have greater effects on your bill, replacing incandescent light bulbs is always a wise choice in the long run:
- You'll recoup the cost of replacing an incandescent light bulb with a CFL in about nine months. The new lamp will also last nine times longer than the old one, saving you even more money in the long run.
- LED lights are even more efficient and have a useful life of around 50,000 hours (nearly six years of constant use). Before you have to change them, they will save you around € 10 per year.
Step 3. Choose the most suitable models to replace the bulbs you own
Consider the following for maximum savings:
- Poor CFL bulbs can burn out quickly. Buy only models with an A + or higher rating.
- If you are lucky, on the package you will find the "lumens", which is an indication of the brightness of the product. If not, follow this approximation: a 60-watt incandescent bulb shines with the same intensity as a 15-watt CFL lamp or a 10-watt LED light.
- Look for a description of the color of the light. "Warm white" is the light closest to the yellow tone of incandescent bulbs. The "Cool White" color sharpens the contrasts, creating an unpleasant feeling in residential environments.
- "Directional" LED lamps concentrate their light in a small area, instead of illuminating a whole room.
Advice
- Watts are the unit of measurement of power, not brightness. A 15W CFL bulb shines with the same intensity as a 60W incandescent because it is more efficient. LED lights are even more efficient and can produce the same brightness with less than 8 watts of power.
- Don't believe the myth that by leaving fluorescent light bulbs on you can save money. Indeed, turning on those lamps requires considerable energy consumption, but leaving them on will certainly consume more.
Warnings
- Check the characteristics of the lamp before switching to a higher power consumption bulb. Each lamp has a maximum wattage. Using a model that is too powerful could cause a short circuit or other damage.
- A light bulb made for a voltage higher than that provided by your electrical system will use fewer watts than indicated on the package. The kilowatt hours absorbed will be less, but the light will be dimmer and more yellow. For example, a 60-watt, 130-volt light bulb powered by a 120-volt circuit will draw less than 60 watts and emit more yellow and dim light than a model designed to operate at 120 V.
