How Much Does a Grow Light Cost to Run in the UK? 2026 Electricity Cost Guide

How much does a grow light cost to run in the UK? The answer depends on three things: the wattage of the grow light, how many hours per day it runs and the electricity unit rate you pay.

Using the current UK average electricity price of 26.32p per kWh as a reference, a 720W LED grow light costs approximately £2.27 to run for 12 hours, or around £68.22 over 30 days when operating at full power.

Run the same 720W LED for 18 hours each day and the cost increases to approximately £3.41 per day or £102.33 over 30 days.

Fortunately, calculating the running cost of any grow light is straightforward once you know its actual power consumption. In this guide we’ll show you the cost of running common 100W, 300W, 600W, 720W, 960W and 1000W grow lights, explain how dimming affects electricity use and show you how to calculate the cost using your own tariff.

If you’re still choosing the correct light for your space, read our LED Grow Light Wattage by Grow Tent Size Guide or browse our range of LED grow lights.

Key Takeaways

• Grow light running cost is calculated using wattage × hours used × electricity price.
• At 26.32p/kWh, a 720W LED costs around £2.27 to run for 12 hours.
• Running a 720W LED for 12 hours every day costs approximately £68.22 over 30 days.
• Running the same light for 18 hours a day costs approximately £102.33 over 30 days.
• A 300W LED running for 12 hours costs approximately 95p per day.
• A 600W grow light drawing a genuine 600W costs approximately £1.90 for 12 hours.
• Dimming can reduce electricity consumption when it reduces the fixture’s actual wall draw.
• Don’t compare LEDs on wattage alone — PPF, efficacy in µmol/J and coverage tell you how effectively the electricity is being converted into useful plant light.
• Fans, pumps, heaters, humidifiers and other equipment also contribute to total grow-room electricity costs.
• For the most accurate calculation, use the price per kWh shown on your own electricity bill.

Quick Answer: How Do You Calculate Grow Light Running Costs?

You can calculate the electricity cost of almost any grow light using this simple formula:

Watts ÷ 1,000 × hours used × electricity price per kWh = running cost

For example, take a 720W LED running for 12 hours at an electricity rate of 26.32p per kWh:

720 ÷ 1,000 = 0.72kW

0.72 × 12 hours = 8.64kWh

8.64 × £0.2632 = approximately £2.27 per day

Over 30 days:

£2.27 × 30 = approximately £68.22

If your electricity tariff is different, simply replace £0.2632 with the price per kWh shown on your own bill.

Grow Light Running Cost Chart UK

The table below shows approximate electricity costs for common grow light wattages using 26.32p/kWh and assumes the fixture is operating at its full stated power.

Important: these figures assume the grow light draws its full stated wattage for the whole lighting period. A dimmed LED may consume substantially less electricity. The figures also exclude your electricity standing charge because that charge would normally be payable whether the grow light was switched on or not.

How Much Does a 720W LED Grow Light Cost to Run?

720W LEDs are now a common choice for larger indoor grow spaces, which makes this one of the most useful running-cost calculations.

At 26.32p per kWh, a 720W LED running at full output costs approximately:

Acorn stocks several current 720W options including the Gorilla 720W LED and Omega 720W Plus LED.

Both consume around 720W at maximum output, but they don’t necessarily produce exactly the same amount of plant-usable light. The Omega 720W Plus, for example, produces approximately 2088 µmol/s at an efficacy of 2.9 µmol/J.

This demonstrates why electricity cost should be compared alongside PPF, PPFD, efficacy and coverage, not wattage alone.

How Much Does a 600W Grow Light Cost to Run?

A lighting system drawing exactly 600W uses 0.6kWh of electricity for every hour it operates.

At 26.32p/kWh:

• 12 hours: approximately £1.90 per day or £56.85 per 30 days
• 16 hours: approximately £2.53 per day or £75.80 per 30 days
• 18 hours: approximately £2.84 per day or £85.28 per 30 days

When comparing this with older HPS lighting, remember that the wattage printed on an HPS lamp does not necessarily represent the complete wall draw of the whole lighting system because a ballast also consumes electricity.

For the most accurate comparison, use the actual input power of the complete system.

How Much Does a 300W LED Cost to Run?

A 300W LED uses 0.3kWh for every hour it operates.

At 26.32p/kWh:

• 12 hours: approximately 95p per day or £28.43 per month
• 16 hours: approximately £1.26 per day or £37.90 per month
• 18 hours: approximately £1.42 per day or £42.64 per month

This is why lower-powered fixtures can be considerably cheaper to operate where a large 600W or 720W light isn’t actually required.

How Much Does a 100W LED Grow Light Cost to Run?

A 100W grow light is relatively inexpensive to operate because it consumes only 0.1kWh per hour.

At 26.32p/kWh:

• 12 hours: approximately 32p per day or £9.48 per month
• 16 hours: approximately 42p per day or £12.63 per month
• 18 hours: approximately 47p per day or £14.21 per month

Lower-output LED lighting can therefore be a cost-effective option for propagation, young plants, herbs, leafy crops and smaller growing areas.

How Much Does a 960W LED Cost to Run?

A fixture drawing 960W at full power uses 0.96kWh every hour.

At 26.32p/kWh:

• 12 hours: approximately £3.03 per day or £90.96 per month
• 16 hours: approximately £4.04 per day or £121.28 per month
• 18 hours: approximately £4.55 per day or £136.44 per month

The LUMii BLACK² 720/960 LED is particularly useful as an example because the modular fixture can operate at different maximum power levels depending on its ballast configuration.

It can operate at up to 720W with one compatible ballast or up to 960W with two, producing up to approximately 2596 µmol/s PPF at maximum output.

How Much Does a 1000W Grow Light Cost to Run?

A genuine 1000W wall draw equals 1kWh of electricity every hour.

At 26.32p/kWh:

• 1 hour: approximately 26.3p
• 12 hours: approximately £3.16
• 18 hours: approximately £4.74
• 12 hours daily for 30 days: approximately £94.75
• 18 hours daily for 30 days: approximately £142.13

This demonstrates why matching the light to the size of the growing area is so important. Buying substantially more wattage than you require can create unnecessary electricity costs.

How Much Does a Grow Light Cost Per Hour?

At an electricity rate of 26.32p/kWh, approximate hourly costs are:

How Much Does a Grow Light Cost Per Year?

The annual cost depends on the lighting schedule and whether the fixture actually runs throughout the entire year.

As a simple example, a 720W LED operating at full output for 12 hours every day at 26.32p/kWh would cost approximately:

£830 per year

Running the same fixture for 18 hours every day would cost approximately:

£1,245 per year

In practice, many growers change lighting schedules and dimmer settings during different stages, so actual annual consumption can be considerably different.

Does Dimming an LED Grow Light Save Electricity?

Yes, provided that reducing the dimmer setting reduces the fixture’s actual wall draw.

If a 720W LED reduced its power consumption approximately in proportion to its dimmer setting, the running-cost difference could look like this:

These are illustrative calculations rather than guaranteed dimmer consumption figures. The actual wall draw at each dimmer setting depends on the fixture and driver.

If you want exact figures, check the manufacturer’s specifications or use a suitable plug-in electricity monitor.

Does a 720W LED Always Use 720 Watts?

No. The 720W rating normally represents the fixture’s maximum electrical input.

If the light is dimmable and operating below maximum output, the actual amount of electricity drawn from the wall should normally be lower.

For accurate running-cost calculations, actual measured wall draw is more useful than simply assuming the fixture always consumes its maximum rated wattage.

Is LED Cheaper to Run Than HPS?

Electricity costs exactly the same per kilowatt-hour regardless of whether it is being used by an LED, HPS lamp, fan or heater.

The potential saving comes from lighting efficiency.

An efficient modern LED may be able to deliver the required amount of usable plant light and canopy coverage while consuming fewer watts than an older HPS setup.

So rather than asking:

“Is LED electricity cheaper?”

A more useful question is:

“How many watts does each system need to deliver the light intensity and coverage I require?”

Why LED Efficiency Matters to Your Electricity Bill

LED grow light efficacy is normally measured in µmol/J.

This tells you how effectively the fixture converts electrical energy into photosynthetic light.

Imagine two LED fixtures that both consume 720W:

• Fixture A produces 1800 µmol/s
• Fixture B produces 2088 µmol/s

Both fixtures would cost approximately the same amount per hour to operate if both genuinely draw 720W, but Fixture B produces more photosynthetic light from that electricity.

This is why the cheapest light to buy isn’t necessarily the cheapest light to own, and why wattage shouldn’t be considered in isolation.

If you’re choosing a new fixture, see our LED Grow Light Wattage by Grow Tent Size Guide for more information on wattage, PPF, PPFD, efficacy and coverage.

How Many kWh Does a Grow Light Use?

Electricity suppliers charge for energy in kilowatt-hours (kWh), sometimes described simply as electricity units.

One kilowatt-hour is the amount of energy used by a 1000W appliance operating for one hour.

For example:

• 100W for 10 hours = 1kWh
• 500W for 2 hours = 1kWh
• 720W for 12 hours = 8.64kWh
• 720W for 18 hours = 12.96kWh

Once you know the number of kWh consumed, multiply it by the unit price on your electricity bill.

Should You Include the Electricity Standing Charge?

Normally, no.

Your standing charge is the daily amount charged for having an electricity supply available to the property and is generally payable regardless of whether your grow light is switched on.

When working out the additional cost caused specifically by your grow light, it therefore makes more sense to calculate using the electricity unit rate only.

Why Your Actual Electricity Cost May Be Different

The examples in this guide use 26.32p/kWh as a current UK reference rate, but your actual electricity cost may be higher or lower.

Your rate can depend on:

• your electricity supplier
• whether you are on a fixed or variable tariff
• where you live
• your payment method
• whether you have a single-rate or multi-rate tariff
• whether your tariff offers cheaper electricity at particular times

For the most accurate calculation, check your latest electricity bill or supplier app and find your current unit rate in pence per kWh.

Can Off-Peak Electricity Reduce Grow Light Costs?

Potentially, yes.

Some tariffs provide cheaper electricity during certain periods of the day or night.

If your lighting schedule and growing environment allow it, operating high-powered equipment during lower-cost periods may reduce overall electricity costs without reducing the amount of light delivered to the plants.

However, tariff structures vary considerably, so always compare the actual peak and off-peak rates before changing a lighting schedule purely for cost reasons.

Use a Timer to Avoid Wasting Electricity

A timer doesn’t reduce the amount of electricity a grow light consumes while it is switched on, but it prevents the fixture being left running longer than intended.

Even one unnecessary hour each day adds up.

For example, one additional hour of a 720W LED every day uses:

0.72kWh × 30 days = 21.6kWh per month

At 26.32p/kWh, this costs approximately:

£5.69 per month

Browse our grow light timers and contactors, including the LUMii 24-Hour Heavy Duty Timer, for automatic daily lighting control.

Don’t Forget the Rest of the Grow Room

The grow light can be one of the largest electrical loads in an indoor growing setup, but it isn’t the only equipment consuming electricity.

You may also be operating:

• extractor fans
• circulation fans
• water pumps
• air pumps
• humidifiers
• dehumidifiers
• heaters
• environmental controllers

Equipment that operates continuously can use a surprising amount of electricity even when its individual wattage seems relatively low.

Example: 50W Fan Running 24 Hours a Day

A 50W fan consumes:

0.05kW × 24 hours = 1.2kWh per day

At 26.32p/kWh, that is approximately:

32p per day

Over 30 days, it works out at approximately £9.48.

If you’re trying to correctly size your extraction equipment rather than unnecessarily oversizing it, read our Grow Tent Extractor Fan & Carbon Filter Sizing Guide and browse our Fans, Filters & Environment range.

How to Reduce Grow Light Electricity Costs

Choose an Efficient LED

Don’t compare fixtures using wattage alone. Look at total PPF output, efficacy in µmol/J, PPFD distribution and usable coverage.

A more efficient fixture can produce more usable plant light from the same amount of electricity.

Match the Light to the Grow Space

A 720W or 1000W LED may be unnecessary in a small growing area.

Choosing the correct fixture size from the beginning avoids paying for electricity you don’t need.

Use our grow light wattage by tent size chart as a starting point.

Use the Dimmer

Maximum light output isn’t required throughout every stage of plant development.

Reducing output when plants need less intensity can lower electricity consumption while also making temperature and environmental control easier.

Use a Reliable Timer

Automating the lighting schedule prevents unnecessary runtime and keeps the photoperiod consistent.

Check Actual Wall Draw

If electricity cost is important to you, use a suitable plug-in energy monitor to find out how much power the complete fixture actually consumes.

Use the Correct Hanging Height

Hanging an LED unnecessarily high can allow useful light to fall outside the growing area, while hanging it too close can create excessively high PPFD in the centre of the canopy.

The objective is to achieve useful, even canopy coverage without using more power than necessary.

Compare Electricity Tariffs

A difference of only a few pence per kWh can become significant when high-powered grow equipment operates for many hours every day.

Frequently Asked Questions

How much does a 720W LED cost to run in the UK?

At an electricity rate of 26.32p/kWh, a 720W LED at full power costs approximately £2.27 for 12 hours, £3.03 for 16 hours or £3.41 for 18 hours. Running it for 12 hours every day for 30 days costs approximately £68.22.

How much does a 600W grow light cost to run for 12 hours?

If the complete lighting system draws exactly 600W, it consumes 7.2kWh over 12 hours. At 26.32p/kWh, that costs approximately £1.90 per day or £56.85 over 30 days.

How much does a 1000W grow light cost to run?

A fixture drawing 1000W consumes 1kWh every hour. At 26.32p/kWh, it costs approximately 26.3p per hour, £3.16 for 12 hours or £4.74 for 18 hours.

Are LED grow lights expensive to run?

It depends mainly on wattage, operating time and your electricity tariff. Small propagation lights may cost only a few pounds per month, while high-output fixtures running for long periods can cost more than £100 per month.

Does dimming a grow light save electricity?

Usually, yes. If dimming reduces the actual wall draw of the grow light, electricity consumption will also fall. The precise saving depends on the fixture and driver.

Does a 720W LED use 720 watts all the time?

Not necessarily. 720W normally represents the maximum input power. A dimmable fixture operating below full output should generally consume less electricity.

Is LED cheaper to run than HPS?

LED can be cheaper where a more efficient fixture delivers the required light intensity and coverage using fewer watts. Electricity itself costs the same per kWh regardless of the lighting technology.

How do I calculate grow light electricity cost?

Divide the fixture wattage by 1,000, multiply it by the number of hours the light operates, then multiply that figure by your electricity price per kWh.

Should I include my electricity standing charge?

Normally not when calculating the additional cost caused by the grow light, because you would usually pay the standing charge whether or not the grow light was operating.

What electricity rate should I use?

Use the price per kWh shown on your latest electricity bill. The examples in this guide use 26.32p/kWh as a current UK reference rate for late 2026, but your tariff may be different.

Final Advice: Calculate the Cost Before Choosing the Light

Working out grow light electricity costs doesn’t need to involve guesswork.

Take the actual wattage, divide it by 1,000, multiply by the number of hours the light operates and then multiply by your electricity price per kWh.

For a 720W LED at the current example rate of 26.32p/kWh, this works out at approximately £68.22 per 30 days when running for 12 hours every day at full power.

However, running cost shouldn’t be considered in isolation.

A lower-powered light isn’t good value if it cannot provide sufficient usable light for the growing area, while an oversized fixture can waste electricity if you never need its full output.

Choose a grow light that matches your space, compare PPF and efficacy as well as wattage, use dimming where appropriate and control the lighting period with a reliable timer.

For help choosing the correct fixture, read our LED Grow Light Wattage by Grow Tent Size Guide, browse our LED grow lights, or explore our grow light timers and contactors.