# Electricity and Energy Terms In Lighting (J, kW, kWh, Lm/W)

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**Are you interested in an energy efficient lighting solution for your organization, business, or facility?**

Picking the most efficient lighting starts with a thorough understanding of energy terminology as it relates to electricity. The four big measures you need to be aware of are **Joules**, **Watts**, **Watt-Hours**, and** Lumens/Watt**. We'll break them down one at a time below.

**Joules (J):**

Joules are the SI (International System of Units) unit of **energy**. They are defined as 1 Joule = 1 kg·m2/s2. If you’re concerned with energy efficiency in lighting, what you’re really trying to do is to minimize the total number of Joules you consume while maximizing the effective light output.

**Watts (W) and ****Kilowatts (kW)****:**

Watts are the SI unit of **power**. Kilowatts are equivalent to 1,000 Watts and are the most frequently used unit of electrical power. Power in general is defined as energy over time. Watts are defined as 1 Watt = 1 Joule per second (1W = 1 J/s) which means that 1 kW = 1000 J/s. A Watt is the amount of energy (in Joules) that an electrical device (such as a light) is burning per second that it’s running. So a 60W bulb is burning 60 Joules of energy every second you have it turned on. In return, you get a particular amount of light, also known as luminance. For more on luminance and an even more important measure (foot-candles), read here.

*Example:* If a room has one hundred 40W light bulbs running at once, you are using 4000 Watts (4000 Joules/second). Imagine getting the same (or better) lighting quality by using one hundred 5W lights instead. Now you’re only burning 500 watts. **That’s only 12.5% as much energy as you were using before; a savings of 87.5%!**

**Watts are an important part of developing your project and product criteria- learn more here!**

**Watt-Hours (Wh) and ****Kilowatt-Hours (kWh)****:**

Imagine you have your 60 Watt bulb on for an entire hour. Enter a new, and sometimes confusing term, “Watt-hours.” Since you ran a 60 Watt bulb for 1 hour, you have used 60 Watt-hours of **energy** (not power). If the owner of a large building (such as a factory or real estate development) is trying to minimize their energy footprint, they want to minimize the number of Watt-hours they are burning throughout a given 24 hour period. This is the same thing as saying they want to minimize the number of Joules they are consuming; it is simply a different, more common unit of measurement. 1 Watt-hour is equal to 3600 Joules (3.6kJ). One Kilowatt-Hour is the same as 1,000 Watt-hours and is the most common unit used in electrical energy consumption.

**Lumens/Watt****:**

This is a unit of measurement for a term called luminous efficacy (you can read about it in detail here). Luminous efficacy is a quantity that describes the amount of illumination (lumens) that you get for a given amount of power (watts). All else being equal, you want to maximize lumens while minimizing the power required to produce them.

**Different devices require different amounts of power to make them run. In addition, different devices emit a different quantity and quality of light for a given power setting. Other major considerations include off-the-shelf price, lifespan, and maintenance/replacement costs. For a more in-depth discussion on the most energy efficient lighting solutions, visit us at** Stouch Lighting **or try our** ROI calculator.** We’re here to help!**