Understanding Watts, Volts, and Amps

Most of the electrical terminology used relates to one another in some way. Understanding each term can help to navigate the complex world of electricity. Here are some electrifying terms everyone should learn.

What are Watts, Volts, and Amps?

All three of these terms are a measure of a unit. Each one measures a different part of an electrical current. From the unit of power to the current rate, these terms cover each part of how the electricity flows. In this article, we want to discuss how these three terms apply to lighting. You will find two of these terms on most spec lighting sheets – watts and volts. Amps, on the other hand, are something your electrician and lighting planner is going to care about.

What is Watts?

Watts is a measurement of the unit of power. Another way to think about it in terms of lighting – watts are what the light fixture consumes to produce light. Watts is also what the electricity company uses to generate your electric bill. (That’s based on per kilowatt, which equals 1000 watts.)

When we discuss lighting, we think a lot in terms of watt savings. Converting from a 400-Watt Metal Halide light to a 150-Watt LED light will save you around 300 Watts (the metal halide also consumes an additional 15% ballast draw). Fewer watts consumed equals more energy savings. And, consequently, lower utility bills.

You shouldn’t confuse watts with how much light a fixture will produce. A light fixture consumes electricity and creates light. There is no universal relationship between watts consumed and light produced in equal amounts.  This is a measure of the efficacy of light – or – efficiency. It can vary from light to light. That is a common misconception in the lighting world.

What are Volts?

Volts come from the power source. They are the unit of measure of pressure on an electrical current. Higher voltage is more ‘efficient’ than lower voltage. In an electrical system, you can increase the power by increasing the current or increasing the voltage.

Our LED fixtures come in a low voltage 100 – 277 or a high voltage 277 – 480. Fixtures that can process a higher voltage use fewer amps than a lower voltage fixture. This allows you to place more fixtures on a circuit. This is beneficial as circuit breakers are restricted by amps, not watts or volts (although they are all related).

For commercial lighting and industrial lighting sites, it is more common to find 240V, 277V, 347V (Canada), and 480V. At home, it’s common to find 100 -120 Volts.

Here are some common voltages and their applications:

What are Amps?

Amperage is the measurement of the rate at which current flows through a circuit. The most important thing to understand with amps is higher voltage allows you to add more fixtures to a circuit. This is important for a few reasons.

Circuits can only handle up to a predefined amp draw that is determined by the circuit breaker. If you have a 20-amp circuit and have fixtures that use 21 amps, it shorts the connection. Being able to add more lights to one circuit is a cost savings.

Industrial facilities are billed based on amp usage. Using fixtures that use fewer amps creates energy savings. Like a fixture using less wattage.

Electricity Equations That Are Easy to Understand

With watts, amps, and volts it’s important to understand the terms and how they apply to lighting. It’s also important to understand the math behind them.

Watts / Volts = Amps
Watts / Amps = Volts
Amps X Volts = Watts

Learning these equations is important. Knowing them and the definitions will help you make sure the circuit isn’t being overrun. It can also help with understanding what’s looked at when speaking with a lighting specialist.

Some Real World “Watts, Volts and Amps” Examples

Metal Halide Installations

400 Watt Metal Halide Fixture in 277 Volt 20 Amp Circuit

• Total Watts: 400 Watt + 60 Watt Ballast Draw = 460 Watts
• Volts: 277
• Amp Draw per Fixture: 1.64
• Total Fixtures allowed on one 20 Amp circuit: 12

1000 Watt Metal Halide Fixture in 277 Volt 20 Amp Circuit

• Total Watts: 1000 Watt + 150 Watt Ballast Draw = 1150 Watts
• Volts: 277
• Amp Draw per Fixture: 4.15
• Total Fixtures allowed on one circuit 20 Amp Circuit: 4

Same Facility After Converting to a Comparable LED Fixture

150 Watt LED Fixture in 277 Volt 20 Amp Circuit

• Total Watts: 150 Watts + 0 Watt Driver Draw = 150 Watts
• Volts: 277
• Amp Draw per Fixture: 0.54
• Total Fixtures allowed on one 20 Amp circuit: 37

300 Watt LED Fixture in 277 Volt 20 Amp Circuit

• Total Watts: 300 Watts + 0 Watt Driver Draw = 300 Watts
• Volts: 277
• Amp Draw per Fixture: 1.08
• Total Fixtures allowed on one circuit: 18