To make this calculation "fair", pick light bulbs that emit a similar amount of light (stated in lumens on the box).
LED bulb
Price
\$
Power consumption
W
hrs
Regular bulb
Price
\$
Power consumption
W
hrs
Usage and energy price
Energy price
\$/kWh
Daily usage
hrs
Cost comparison and break even point
Over how many years?
yrs
LED total cost
\$
Reg. bulb total cost
\$
Total savings
\$
Break even after
mos

# LED Savings Calculator

By Steven Wooding

The LED savings calculator shows you how much money you could save by switching to LED light bulbs. Simply input the details of your old, inefficient incandescent bulb, how much you use it, and the features of the LED bulbs you are thinking of buying.

Our LED light bulb savings calculator shows you the total cost of buying bulbs over your choice of duration, the total LED cost savings, and how long it is before you start saving money. Spoiler! It's shorter than you think!

## Incandescent light bulbs - or should that be heat bulbs?

The incandescent light bulb, made famous by Thomas Edison, works by passing an electric current through a thin tungsten filament whose electrical resistance is such that it starts to heat up and produces light as a side effect.

Only 5% of the energy consumed by an incandescent bulb goes into creating light. The rest produces heat. Perfect if you want to keep some fluffy little chicks warm, but not very bright if you're going to light your house. That's why incandescent light bulbs should really be called "heat bulbs".

## What are LED light bulbs? - LED light bulb savings

Over the years, improvements in light bulb technology are such that they now produce less heat and more light as a proportion of their energy use. The latest and greatest technology is LED, which stands for Light-Emitting Diode. These are small electronic components that produce light when provided with an electric current. Each LED can only emit a small amount of light, so bulb manufacturers make a single bulb out of multiple LEDs. For the same amount of light output, LEDs use around 83% less energy than incandescent light bulbs.

Incandescent light bulbs blow because the tungsten filament burns out, due to all that heat. As LEDs run a lot cooler and employ more sophisticated semiconductor electronics, they can last from 15 to 40 times longer than incandescent light bulbs. That means you don't have to change them so often. This advantage is a significant factor to consider when looking at the price of LED bulbs. The replacement costs of incandescent bulbs can add up very quickly.

## Calculating total LED light bulb cost (including replacement)

The total cost of a light fitting has two components. The cost of electricity the bulb uses and the cost of replacing the bulb when it expires. We can write down an equation that computes the total cost over a year by adding these two components together:

`total cost = cost of electricity + cost of replacing`

where:

`cost of electricity = (consumption / 1000) * (daily usage * 365.25) * energy price`

`cost of replacing = bulb price * ceil((daily usage * 365.25) / lifetime)`

where:

• `ceil()` is a math function that rounds up to the next whole integer, and helps to calculate the number of bulbs;
• `daily usage` is the amount of hours per day, on average, the bulb is in use;
• `lifetime` is the number of hours, on average, until the bulb expires;
• `consumption` is the power consumption of the bulb, in Watts;
• `energy price` is the cost of electricity per kilowatt-hour (kWh); and
• `365.25` is the number of days, on average, in a year.

The part of the equation `ceil((daily usage * 365.25) / lifetime)` calculates how many bulbs will be required for a year. For an LED, this is likely to be one. Whereas if an incandescent bulb is left on all day, you could need a total of nine bulbs per year.

To calculate how long it will take before you starting saving money by using the more efficient, longer-lasting LED bulbs, we can simply do:

`break-even point = (led total cost / incandescent total cost) * 12`

Multiplying by 12 gives the break-even point in months.

## How to use the LED savings calculator?

The basic idea is that you input the details of the LED bulb you are looking to buy, and that of your current incandescent light bulb. Then enter your electricity price, and how much you use that light. You can then compare the total costs and savings over several years, along with the break-even point, after which the LED bulb starts saving you money.

To make it a fair comparison, make sure the bulbs output similar amounts of light, usually stated in the bulb specifications in lumens or lux. For example, a 60 W incandescent bulb and a 10 W LED bulb output a light level of around 800 lumens, while a 100 W incandescent bulb outputs 1,600 lumens, which is the equivalent of a 16 W bulb.

Let's now go through the process of using the LED savings calculator, step-by-step:

1. Enter the price of the LED bulb you are thinking of buying;
2. Input its power consumption in Watts (W);
3. Check the expected lifetime of the LED bulb. The default is 15,000 hours, but it could be as much as 40,000 hours;
4. Enter the same details for your current regular incandescent bulb;
5. Input the electricity price you pay per kWh (or unit). You can find this information on your electricity bill;
6. Estimate how long the light will be on each day (well, night more likely); and
7. By default, the calculator will show you the total cost of each bulb, and the possible savings over one year. However, if you want to calculate these figures over a more extended period, change the value when asked: "Over how many years?".

You could also use this LED light bulb cost calculator to compare an LED bulb to other inefficient bulb types, such as halogen and compact fluorescent light (CFL) bulbs, so, you can also use it as an LED vs fluorescent energy savings calculator.

## An example of using the LED cost saving calculator

Let's go through an example calculation and see how much you could save using the LED cost saving calculator. The LED light bulb cost you are looking to buy is \$2.00, consumes 10 W, and has a lifetime of 15,000 hours. You see on your electricity bill that the electric company charges \$0.12 per kWh, and you estimate that you use the bulb for 3 hours a day. Now we have enough information to calculate the cost of the LED for the first year.

`LED cost = \$2.00 * ceil((3 hrs * 365.25) / 15,000 hrs)) + (10 W / 1,000) * (3 hrs * 365.25) * \$0.12/kWh)`

`LED cost = \$2.00 * 1 bulb + 0.010 kW * 1,095.75 hrs * \$0.12 /kWh`

`LED cost = \$2.00 + \$1.32 = \$3.32`

The cost calculation shows that we only need one bulb for the first year, and it's going to cost \$1.32 in electricity to run it. Now let's see how our old incandescent bulb compares.

The incandescent light bulb has a replacement cost of \$0.50, consumes 60 W, but only lasts 1,000 hours. Now we'll calculate its total cost.

`incandescent cost = \$0.50 * ceil((3 hrs * 365.25) / 1,000 hrs)) + (60 W / 1,000) * (3 hrs * 365.25) * \$0.12 /kWh)`

`incandescent cost = \$0.50 * 2 bulbs + 0.060 kW * 1,095.75 hrs * \$0.12 /kWh`

`incandescent cost = \$1.00 + \$7.89 = \$8.89`

You'll probably need to replace the bulb in the first year, but the total bulb cost is still lower than the LED. However, the electricity cost is six times the cost of the LED bulb. Over the first year, you will save \$6.10. How long into the year until you start saving with the LED bulb?

`break even point = (\$3.32 / \$8.89) * 12 = 4.5 months`

Even though the LED bulb costs more to buy than the incandescent light bulb, the lower electricity cost means you will start saving money after just a few months.

If you do the cost calculations again, but this time over five years, you'll find that the total cost for the LED bulb is \$8.57 compared to \$42.45 for the incandescent bulb. That's a saving of \$33.88, just for one light fitting. What if you switched all the bulbs in your house to LED bulbs? Just think of the savings then.

Another point is that you would have to change the incandescent bulb around five times over those five years, while you wouldn't have to change the LED bulb at all. That's great, as who wants to spend time changing bulbs?

Steven Wooding