How To Calculate Your Light Savings When Replacing Incandescent Bulbs

The news about saving money and electricity by replacing old light bulbs is old news (unless you’ve been living under a rock). But the topic of saving light is not exaggerated yet. Suppose that every household in the US would switch to high-efficiency light bulbs (such as CFLs). This would reduce the nation’s energy consumption by 10% in the residential sector. The residential sector, by the way, accounts for about 20% of all energy use in the US That’s a lot of oil.

Still not sure about switching to high-efficiency bulbs? Don’t believe the hype about saving light? You do not believe in the positive impacts on your pocket or the environment? Do you want to calculate and test the light savings for yourself? Well, let’s tackle cost savings and simple recovery below. (Simple amortization refers to the amount of time it takes you to recoup the cost of the new bulbs with the savings.)

To calculate the final result, here is the necessary information:

• The power rating (watts) of the existing bulb
• The power rating (watts) of the new bulb.
• The number of hours we use the bulb every day.
• The rate we pay for electricity in kilowatt-hours or kWh. You can find your electric rate by looking at the electricity portion of your utility bill.
• A kilowatt is 1000 watts, so we must remember to divide our answer by 1000 to convert it to kilowatt-hours.
• The cost of the original bulb.
• The cost of the new bulb

As an example, let’s change a heavily used light bulb into a fixture in a living room that is on continuously for 5 hours a day. The fixture has a 100-watt incandescent bulb that costs $ 050. It must be replaced by a 25-watt compact fluorescent or CFL (provides the equivalent brightness of incandescent), at a cost of $ 2.50. Let’s assume $ 0.15 per kilowatt hour (kWh) for the electricity rate, the national average in the US.

To calculate cost savings, first calculate the energy use of the existing bulb, then that of the replacement bulb. Hopefully, the power usage of the replacement bulb will be less than that of the existing bulb. The difference between existing and new is savings. Here is the formula to calculate the cost of energy used per year:

Annual energy cost ($) = number of bulbs X watts per bulb / 1000 watts X hours of use per day X 365 days X electricity rate

So for our example:

Energy cost for existing light bulb ($) = 1 light bulb X 100 watts X 5 hours per day X 365 days X $ 0.15 per kWh / 1,000 watts = $ 27.38 per year

Energy cost per replacement bulb ($) = 1 bulb X 25 watts X 5 hours per day X 365 days X $ 0.15 per kWh / 1000 watts = $ 6.84 per year

Savings per year ($) = $ 27.38 – $ 6.84 = $ 20.54

Here’s how to calculate simple payback in years:

Simple amortization (years): (Cost of new bulb ($) – Cost of old bulb ($)) / annual savings ($)

For our example, the simple recovery is:

Simple amortization (years) = ($ 2.50 – $ 0.5) /$20.54 = 0.1 years or 1.2 months

That’s not a bad return on investment for saving light. An average house has between 15 and 20 light bulbs. If they were all the same as in the previous example, that would result in a savings of about $ 411 per year. You can use the same method to calculate the savings for each room in your home and add up all the savings in the room to get a total of your annual savings.

You can check your savings by monitoring your utility bills from month to month, as long as your rates stay the same and you do not change the hours of operation of the bulb. Even with proven savings, there still seem to be objections to replacing incandescent bulbs with compact fluorescent lights (or CFLs) or light-emitting diodes (or LEDs), otherwise this would be a “done deal”.

LEDs provide even greater savings (90% light savings) and longer lifespan (25,000-50,000 hours) and will be the dominant technology in the intermediate future. They are also more environmentally friendly to produce and are less susceptible to breakage or moisture. But at this point, its main drawbacks are its high price and lower light output (or lumens) compared to incandescent bulbs. However, technology advances very quickly, and once prices fall to reasonable levels, these problems will be a fleeting memory.

CFLs, on the other hand, are much more accessible and affordable, and have come a long way to closely match the light output and utility of incandescent bulbs. A repeated complaint about them is that CFLs need to warm up to reach full brightness, but that is usually on the order of seconds to a minute for specialty bulbs. They are also affected by humidity and humidity.

While the cost of CFLs is still higher than a $ 0.50 incandescent bulb, prices have dropped to affordable levels for replacements, typically on the order of $ 1.50 to $ 4.50 per bulb. depending on the type. The average lifespan of CFLs is 8,000 hours (or roughly five years at four hours per day of use), while incandescent bulbs are rated for 800-1,200 hours. One thing is worth noting for light saving calculations. The life of CFLs is shortened if they are turned on and off frequently. If you plan to install them in areas where they will be changed frequently, reduce their life by 20% to 6,400 hours.

What about the mercury in CFLs? The amount of mercury in a CFL is 5 mg or about 1/100 the amount of mercury in a dental filling (500 mg in dental fillings). More specifically, the mercury used by a power plant to make an incandescent light bulb is 10 mg, while for a compact fluorescent it is approximately 2.5 mg. However, broken light bulbs should be handled with care and burned out light bulbs should be disposed of at household centers such as Home Depot and Ikea.

No matter how we look at it, saving light by replacing incandescents is one of the easiest and cheapest methods of incorporating energy efficiency and achieving energy savings at home. Many countries have started to systematically phase out the production of incandescent light bulbs. The economy is there and the environmental benefits will only improve as technology advances.