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How much power does a light bulb use, and also how does lighting influence your electrical energy bill? just how much will a lighting retrofit save you? exactly how do you begin to estimate the value of a potential bright rebate?

There’s one typical thread that runs v each of these questions: the difference between watts (W), kilowatts (kW), and also kilowatt-hours (kWh). Calculating watts to kWh could aid you recognize the answers come the questions above.

You are watching: A 100w light bulb is left on for 10 hours

The energy industry is almost as negative as the lighting industry at using abbreviations and also jargon, therefore we’ll shot to break every of this down through some handy examples.

In this article, i’m going to use the analogy of equating power to water. This is a common analogy that we can’t case as our own, however hopefully our particular examples will aid explain just how much power lighting really uses.

If you currently know the difference in between kW and also kWh, click below to run ahead come the calculator.

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What is a watt (W)?

You’ve most likely made a many lighting decisions based upon wattage. Friend unscrew a burned out irradiate bulb and also look at the top and see “60W.” every you have actually is a light bulb labeled “25W,” so girlfriend screw it in, and to her dismay, it’s means too dim. You go to the store and also pick out a “60W” bulb. Your lights space bright again. Crisis averted.

So what is a watt, anyway? Technically speaking, it"s a unit of electrical power same to 1 joule per second. Irradiate bulbs room rated in watts to indicate exactly how much energy they consume.

Does the wattage the a light bulb have anything to execute with brightness? Well, type of.

For so long, plenty of of us have associated watts through the quantity of irradiate a bulb gives off. In general, that functions well with timeless incandescent irradiate bulbs. A 60W incandescence bulb generally gives off approximately 650-800 lumens. A 25W incandescent bulb typically produces roughly 150 lumens — much much less light.

With the introduction of more efficient lighting, though, that not unusual to check out a “60W equivalent” bulb that uses far less energy and also gives off roughly the exact same amount that light. This is a breakdown:

IncandescentHalogenCFLLED
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Wattage60W42W13-16W5-9W
Lumens per watt (LPW)1318.56075-100+

(The photos above are representative that the technology, not particular product specifications.)

So, as you space comparing irradiate bulbs, remember that wattage is a measure of how much energy the light pear will use as that produces light, and the lumens will provide you a measure up of just how much irradiate it will certainly produce.

Ready to shop light bulbs? Click here and use the filter on the left to kind by lumens.

What is a kilowatt (kW)?

Just favor watts, kilowatts is a measure of exactly how much power something will consume. Walk from watt (W) come kilowatts (kW) is a pretty straightforward calculation: 1kW is equal to 1,000W. To transform W to kW, divide the total wattage through 1,000.

Here’s an example: if friend turned on ten 100W irradiate bulbs, that would equal 1kW of energy usage.

10 bulbs x 100W = 1,000W

1,000W / 1,000 = 1kW

It’s also worth noting that kW have the right to be synonymous with “demand” if you’re talking to a utility company. Imagine the you turn on those ten irradiate bulbs and also a 3,000-watt clothes dryer in ~ the very same time. The utility agency needs to have the ability to supply enough electrical energy to accomplish that 4kW of need at the moment you turn everything on.

Your power usage, though, depends on how long girlfriend keep everything on, i m sorry leads united state to…

What is a kilowatt-hour (kWh)?


What’s the difference in between kW and also kWh? The kWh measure up is a method to quantify exactly how much power is provided over a period of time. This can be calculated by multiply the kW that energy usage by the total variety of hours the lighting has actually been operated.

Let’s go back to the example of having ten 100W irradiate bulbs. Exactly how much energy would you usage of the course of a month if you turn them on because that 10 hours a day?

That’s whereby kWh comes into play. Here’s the breakdown:

10 bulbs X 100W = 1,000W or 1kW that lighting

10 hrs of day-to-day use X 30 job in the month = 300 hours of use

1kW X 300 hours of use = 300kWh of energy consumption

So why is kWh so essential if you deserve to compare bright products based on wattage and also light output? In the end, a far-reaching portion that your electricity bill is based upon your energy intake in kilowatt-hours. If you desire to calculation the disagreement savings you’ll acquire from a retrofit to an ext efficient lighting, kWh will come into play.

kW vs kWh: A useful example

Okay, sufficient theory.

How about a practical example to describe the difference in between kW and kWh? (Here’s where the water analogy comes in.)

Let’s imagine that we have two garden hoses, one through a 3/8-inch diameter and also one v a 5/8-inch diameter.


The 5/8-inch hose has actually a bigger capacity 보다 the 3/8-inch hose, so it have the right to carry much more water at any type of given moment. This is the idea of kW — the capacity to use electricity.

Now, let’s imagine the we desire to to fill up a two-gallon watering can. The lot of water the we usage to to fill up the can is 2 gallons. This is the idea the kWh — the total amount of power consumed end time.

How long would it require to fill increase the watering can? That relies on i m sorry hose us choose. The 5/8-inch water tap — because of the larger capacity — will certainly fill increase the watering can an ext quickly than the 3/8-inch hose.

In the same way, a 100W light bulb will consume a total of 10kWh of energy faster than a 60W irradiate bulb.

Here is a parallel example:

WaterEnergy
Step 1: Capacity
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Let’s usage our 5/8” diameter hose which we will certainly assume tote 16 gallons every minute
Let’s usage a 60W (0.06kW) glow bulb
Step 2: TimeLet’s run the hose for 20 minutesLet’s operate the light pear for 2,000 hours
Step 3: Consumption16 gal/ min x 20 min= 320 festival consumed0.06 kW x 2,000 hrs = 120 kWh consumed

Let’s carry in the performance piece come the example and also compare an glow light pear to one LED light bulb:

EnergyEnergy
Step 1: Capacity60W (0.06kW) glow bulb5W (0.005kW)LED bulb
Step 2: TimeLet’s run the light pear for 2,000 hoursLet’s run the light pear for 2,000 hours.
Step 3: Consumption10.06 kW x 2,000 hrs = 120 kWh consumed0.005 kW X 2,000 hrs =10 kWh consumed

In this example, we got the exact same light output, and also we operated the light bulbs because that the exact same amount of time, however the total energy consumption over the 2,000 hrs of procedure was 110 kWh much less for the LED bulb.

W vs kWh in light rebates


Lighting rebate programs room one area wherein we often tend to view the difference in between a wattage reduction and kWh usage reduction on a consistent basis.

In general, there are two kinds of lighting rebates we run across:

1. Demand-reduction bright rebates

Some light rebates are focused on the wattage palliation of a retrofit. If you replace a 100W PAR38 bulb v a more efficient 14W LED PAR38, the utility will salary a rebate based on the 76 watts of power reduced.

2. Usage-reduction light rebates

Other bright rebates are concentrated on the in its entirety reduction in energy usage for a retrofit. If you operate your lighting for 4,320 hours per year (12 hours per day, 360 days per year), the 100W PAR38 would usage 432 kWh every year and also the 14W LED PAR38 would use just over 60 kWh per year.

In this case, the energy would salary a rebate based on the 372 kWh the energy consumption saved over the food of the year from the much more efficient lighting.

Trying to make feeling of the myriad of lighting rebates obtainable throughout the country?We"re below to help.

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Hopefully our explanation that the difference between watts, kilowatts, and also kilowatt-hours is helpful.

We want to make this as basic as possible, so we’ve put together a calculator that you have the right to use to easily — and also easily — gain the number you need.

Watts come kWh calculator


Now that you’re a pro at knowing the difference in between kW and also kWh, examine out our write-ups on understanding the total cost of bright or how to calculate power savings and payback because that lighting projects.