Understanding Watts, Volts, and Amps When It Comes to LED Lighting

Most electrical terminology is related in some way, and understanding the basics makes it easier to navigate lighting specs and electrical conversations. Below are practical definitions and examples of watts, volts, and amps as they apply to lighting.

Safety note: This article is for general education only. Circuit design, fixture quantities per circuit, and installation requirements must follow the NEC (or applicable local code) and be verified by a licensed electrician or qualified engineer.

Watts vs. Volts vs. Amps

These three terms describe different parts of an electrical system:

• Watts (W) = power (how much energy a fixture uses at a given moment)
• Volts (V) = electrical “pressure” (the supply level provided by the building)
• Amps (A) = current (the flow rate of electricity on a circuit)

On most lighting spec sheets you’ll see watts and voltage. Amps matter most for circuit loading, breaker sizing, and conductor selection-typically handled by an electrician or lighting planner.

What Are Watts?

Watts measure power. In lighting terms, watts are what a fixture consumes to produce light. Your utility bill is based on energy use over time (kWh), where 1 kW = 1,000 watts used continuously for one hour.

For example, converting a 400W metal halide to a 150W LED fixture can dramatically reduce energy use. Metal halide systems also commonly draw additional ballast power (often estimated around ~15%, though actual ballast draw varies by system).

Important: Watts do not tell you how bright a fixture looks by themselves. Brightness is better estimated by lumens, distribution (optics), mounting height, and application.

There is no universal one-to-one relationship between watts consumed and light produced. Efficiency (often called efficacy, measured as lumens per watt) varies widely by product and design.

What Are Volts?

Volts come from the power source (your building’s electrical system). Voltage is the “pressure” that pushes current through a circuit.

It’s common to hear that “higher voltage is more efficient.” A more accurate way to say it is:

• For the same wattage, a higher voltage load draws fewer amps.
• Lower amps can reduce conductor losses and often allows more fixtures per circuit (subject to code and design).

Our LED fixtures commonly use either 100-277V drivers or 277-480V drivers depending on the product and application.

For commercial LED lighting and industrial LED lighting sites, you’ll frequently see 208V, 240V, 277V, 347V (Canada), and 480V.

Here are common voltages and where they’re typically used (actual site conditions vary):

What Are Amps?

Amps measure the rate of electrical current flowing through a circuit. For lighting projects, amps matter because breakers, conductors, and panels have maximum current limits. If a circuit is overloaded, it can trip a breaker and create safety hazards.

Higher voltage often means fewer amps for the same wattage, which can allow more fixtures per circuit, but circuit design must follow code.

Billing clarification: Most utility bills are based primarily on kWh (energy use). Many commercial/industrial bills also include demand (kW) and sometimes power factor charges. Amp draw is mainly a design and safety concern for circuits.

Electricity Equations That Are Easy to Use

These three formulas are the basics for lighting calculations:

• Watts ÷ Volts = Amps
• Watts ÷ Amps = Volts
• Amps × Volts = Watts

Knowing these helps you understand circuit loading and what’s being reviewed when speaking with a lighting specialist.

Real-World “Watts, Volts, and Amps” Examples

Important: The examples below use a common guideline for continuous loads where a 20A circuit is often planned at 80% (16A usable). Always confirm requirements with your electrician and local code.

Metal Halide Installations

400W Metal Halide Fixture on 277V (20A Circuit Example)

• Total watts (estimated): 400W lamp + ~60W ballast draw = 460W
• Volts: 277V
• Amp draw per fixture: 460 ÷ 277 = 1.66A
• Estimated fixtures on one 20A circuit (at 16A usable): 16 ÷ 1.66 = 9 fixtures

1000W Metal Halide Fixture on 277V (20A Circuit Example)

• Total watts (estimated): 1000W lamp + ~150W ballast draw = 1150W
• Volts: 277V
• Amp draw per fixture: 1150 ÷ 277 = 4.15A
• Estimated fixtures on one 20A circuit (at 16A usable): 16 ÷ 4.15 = 3 fixtures

Same Facility After Converting to Comparable LED Fixtures

150W LED Fixture on 277V (20A Circuit Example)

• Total watts: 150W (driver losses exist but are already reflected in input watts)
• Volts: 277V
• Amp draw per fixture: 150 ÷ 277 = 0.54A
• Estimated fixtures on one 20A circuit (at 16A usable): 16 ÷ 0.54 = 29 fixtures

300W LED Fixture on 277V (20A Circuit Example)

• Total watts: 300W
• Volts: 277V
• Amp draw per fixture: 300 ÷ 277 = 1.08A
• Estimated fixtures on one 20A circuit (at 16A usable): 16 ÷ 1.08 = 14 fixtures

Get Professional Electrical Calculations for Your Lighting Project

Understanding watts, volts, and amps is a strong starting point, but real projects require site-specific verification. At LED Lighting Supply, our experienced product specialists help you select fixtures that match your voltage, circuit capacity, and performance requirements. We provide complimentary energy-savings estimates that factor in operating hours and local utility rates.

We can also create custom lighting plans tailored to your facility layout and application needs, helping you avoid common issues like improper fixture spacing, insufficient light levels, or circuit overloading.