Skip to content
Sprout & Spectrum

How Much Electricity Do Grow Lights Use?

Less than almost everyone assumes. Here is the exact figure for each fixture we cover, and what it looks like next to the rest of your house.

By Scooter M. — An enthusiast who's genuinely into this. I read the manuals, compile the published specs, and do the math. No lab coat.

Published · How we pick

An electricity meter mounted on an exterior wall

Photographs on this site are licensed stock and are illustrative of the fixture type. We do not own the units we write about.

How this page is funded: the buy links here are Amazon Associates links, and we earn a commission on qualifying purchases at no extra cost to you. We have not been paid to feature anything on this page, we accept no free product, and commission plays no part in the ranking. Full disclosure.

We have not tested these units. Everything below comes from the manufacturer’s own published specifications, or from arithmetic we have shown our working for. Where a figure is not published, we say so instead of estimating one. Read the method.

Quick picks

Efficacy is photons out per joule in. Where a manufacturer publishes it we quote theirs; where they publish photon output and wattage but not efficacy, we divide and label it as ours; where they publish neither, the cell says so rather than guessing. Tap a row for the full write-up.

#ProductBest forEfficacyPrice
1
Linked LED strip lights mounted under a wire shelf above trays of seedlings
Barrina T5 4ft Grow Light Strips
The default seed-starting bar for good reasons — 4 ft long, linkable in series, cheap per foot — and the reason we built a coverage calculator, because Barrina publishes no photon data whatsoever.
20 W per stripNot published
2
A screw-in LED grow bulb in a desk lamp aimed at a potted houseplant
SANSI 36W BR30 Grow Light Bulb
The rare grow bulb that publishes both PPF and a PPFD figure with the measurement distance attached, which is the only reason it can be sized honestly.
36 W for one plant1.82 umol/J (ours)
3
A square white LED grow panel hanging above leafy seedlings indoors
Spider Farmer SF1000
Publishes PPF to two decimal places and an efficacy figure that actually divides out of it. That internal consistency is rarer in this category than it should be.
100 W for a shelf2.5 umol/J

The reasoning

The answer is a multiplication, so let us do it for every fixture on this site rather than describing it in the abstract. All figures below assume 14 hours a day for 30 days, at the US residential average of 18.34 cents per kWh. Change any of those and the numbers scale proportionally.

kWh per month = watts × hours × 30 ÷ 1000
Cost = kWh × rate

Every fixture we cover, per month

Monthly consumption at 14 hours a day, computed from published rated power
FixtureRated powerkWh/monthCost at 18.34¢
GooingTop clip lightabout 10 W4.2$0.77
Barrina T5, one strip20 W8.4$1.54
SANSI 36W BR3036 W15.1$2.77
Soltech Aspect Gen 236 W15.1$2.77
Spider Farmer SF1000100 W42.0$7.70
VIVOSUN VS1000100 W42.0$7.70
ViparSpectra P1000100 W42.0$7.70
AC Infinity IONBOARD S22115 W48.3$8.86
Mars Hydro TS 1000150 W63.0$11.56
Barrina T5, eight linked strips160 W67.2$12.32

What that is, in household terms

The most useful thing to know is not the kWh figure but where it sits against loads you already pay for without thinking. A 100 W grow light on 14 hours a day draws 1.4 kWh daily. For comparison, within a typical home that is broadly comparable to running a modern refrigerator, and a small fraction of what a 1500 W space heater consumes in a couple of hours.

A grow light against a space heater

A 1500 W space heater run for 2 hours: 1500 × 2 ÷ 1000 = 3.0 kWh.

A 100 W grow light run for 14 hours: 100 × 14 ÷ 1000 = 1.4 kWh.

The heater uses more than twice as much in two hours as the grow light uses all day. If your winter bill jumped, heating is a far more likely explanation than the shelf of seedlings.

The two things that actually move the number

  • How many fixtures. This is the big one. A three-shelf rack with two 4 ft bars per shelf is six strips: 120 W, not 20. People price one fixture and buy six.
  • How many hours. Going from 12 to 16 hours a day is a third more electricity. That is usually a good trade — it is the cheapest way to raise daily light integral — but it should be a decision rather than an accident.

Efficacy matters too, but indirectly: a more efficient fixture lets you hit the same light level at a lower draw. That is the subject of the most efficient grow lights by µmol/J.

A realistic whole-setup example

A three-shelf seed-starting rack, February to April

Two Barrina 4 ft strips per shelf, three shelves: 6 × 20 W = 120 W.

At 16 hours a day: 120 × 16 ÷ 1000 = 1.92 kWh a day.

Over 10 weeks (70 days): 134.4 kWh.

At 18.34 cents per kWh: $24.65 for the entire season.

That is the whole electricity cost of starting every transplant you will plant out in spring. It is roughly the price of the seedlings it replaces.

Run your own configuration through the running-cost calculator, and if you are worried about the bill specifically, we take that apart in do grow lights raise your electric bill.

Every pick in full

Linked LED strip lights mounted under a wire shelf above trays of seedlings
01

Barrina T5 4ft Grow Light Strips

LED bar

20 W per strip

The default seed-starting bar for good reasons — 4 ft long, linkable in series, cheap per foot — and the reason we built a coverage calculator, because Barrina publishes no photon data whatsoever.

What Barrina publishes

Power draw
20 W per fixture; an 8-pack draws 160 W (source)
Spectrum
5000 K (source)
Dimming
No; on/off switch per fixture, linkable up to 8 in series (source)
Dimensions
4 ft strip, 120-degree beam angle, 120 V AC (source)

What Barrina does not publish

  • PPF in umol/s — for any strip in the range
  • PPFD at any stated distance
  • Photon efficacy in umol/J
  • LED count per strip, and rated lifespan

Who should skip it

Skip it if you need to know what you are getting before it arrives. There is no published PPF, no PPFD and no efficacy figure, so nothing about its output can be verified in advance.

A screw-in LED grow bulb in a desk lamp aimed at a potted houseplant
02

SANSI 36W BR30 Grow Light Bulb

Grow bulb

36 W for one plant

The rare grow bulb that publishes both PPF and a PPFD figure with the measurement distance attached, which is the only reason it can be sized honestly.

What SANSI publishes

Power draw
36 W (source)
PPF (photon output)
65.6 umol/s (source)
PPFD
265.58 umol/m2/s at 1 ft (source)
Spectrum
4000 K, 400-780 nm, CRI close to 100 (source)
Rated life
25,000 hours (source)

Our arithmetic

  • Efficacy, computed from the published figures: 1.82 umol/J
    65.6 umol/s / 36 W = 1.82 umol/J. That is roughly a third less efficient than the panels on this page — the price of a screw-in form factor.
  • Electricity used at 12 hours a day for 30 days: 12.96 kWh a month
    36 W x 12 h x 30 d / 1000 = 12.96 kWh.

What SANSI does not publish

  • Beam angle
  • Fixture dimensions

Who should skip it

Skip it if you are lighting more than one plant. 65.6 umol/s is a small amount of light spread over a cone — it lights a single specimen, not a shelf.

A square white LED grow panel hanging above leafy seedlings indoors
03

Spider Farmer SF1000

LED panel

100 W for a shelf

Publishes PPF to two decimal places and an efficacy figure that actually divides out of it. That internal consistency is rarer in this category than it should be.

What Spider Farmer publishes

Power draw
100 W +/-5% at 100-277 V AC (source)
PPF (photon output)
249.21 umol/s (source)
Efficacy
2.5 umol/J (source)
Stated coverage
2 x 2 ft core, 3 x 3 ft maximum (source)
Spectrum
650-665 nm, 730-740 nm, 2800-3000 K, 4800-5000 K (source)
Diodes
Bridgelux (source)
Dimming
Yes, dimming knob (source)
Dimensions
32.5 x 29.0 x 5.9 cm (source)
Rated life
55,000 hours (source)

Our arithmetic

  • Does the published efficacy check out against the published PPF?: Yes — 2.49 umol/J computed against 2.5 umol/J published
    249.21 umol/s / 100 W = 2.4921 umol/J. The published 2.5 umol/J is that number rounded. Not every brand's two figures agree like this, which is exactly why we divide them.
  • Average PPFD across its 2 x 2 ft core footprint: about 536 umol/m2/s
    2 ft x 2 ft = 4 sq ft = 0.372 m2. 249.21 / 0.372 = 670 umol/m2/s at perfect uniformity; at a 0.8 uniformity factor, about 536 umol/m2/s.

Who should skip it

Skip it if raw output is what you are buying — the TS 1000 delivers 38% more photons per second, at the cost of 50 W more draw.

Questions people actually ask

+How much electricity does a 100W grow light use?
About 1.4 kWh a day at 14 hours, which is 42 kWh a month and roughly $7.70 at the US residential average of 18.34 cents per kWh. Change the hours and it scales directly.
+Are grow lights expensive to run?
Not at home scale. Most single-fixture setups land between one and twelve dollars a month. The cost only becomes noticeable with several hundred watts running long hours for months, and even then it is typically tens of dollars rather than hundreds.
+Do grow lights use more electricity than a TV?
It depends on the hours far more than the wattage. A modern television draws more when it is on, but runs a few hours a day; a grow light draws less but runs 14 or 16. Over a month the grow light often uses more, which is the general lesson: duration dominates.
+Does dimming a grow light save electricity?
Yes, roughly in proportion. Running a 100 W panel at 50% draws about half the power and delivers about half the photons, which is worth doing when you are over your target light level rather than under it.

Sources

Read next

Where this sits

This page belongs to Running Cost and Efficiency. Every figure on it is either quoted from a named published source or derived in view — the full method is on our methodology page, and how the site is funded is on the affiliate disclosure.