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Sprout & Spectrum

Shop Light vs Grow Light for Seedlings

The shop light usually works. The problem is that you cannot find out whether it will before you buy it.

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

A metal wire shelving rack set up with lighting for indoor plants

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.
Shop-light shapeNot published
2
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.
Actual photon specs2.5 umol/J

The reasoning

Gardeners have raised excellent seedlings under plain white shop lights for decades, and the internet’s insistence that you need a purpose-built horticultural fixture is mostly wrong. Seedlings are driven by intensity far more than by exotic spectrum, and a modern white LED shop light produces plenty of usable photons.

There is one real difference, and it is not about the light. It is about the specification.

The unit problem

A shop light is sold in lumens. A grow light — a good one — is sold in PPF, in µmol/s. These measure different things and are not interconvertible without knowing the fixture’s exact spectrum.

  • Lumens weight light by the sensitivity of the human eye, which peaks in the green around 555 nm — the region plants reflect most, which is why leaves look green.
  • PPF counts every photon between 400 and 700 nm equally, because that is the range that drives photosynthesis.

A fixture heavy in green light scores well in lumens and poorly for plants. A fixture heavy in deep red scores poorly in lumens and well for plants. So a lumen figure cannot be converted into a PPFD figure, and any published conversion factor has silently assumed a spectrum. We do not publish one, and you should distrust anyone who does.

Shop light versus horticultural fixture, for a seedling shelf
White LED shop lightHorticultural LED
Will it grow seedlings?Yes, if it is bright enough and close enoughYes
Published inLumens, and sometimes wattsPPF (µmol/s) and often efficacy (µmol/J)
Can you size it before buying?No — no photon figure exists to divideYes, if the manufacturer publishes PPF
SpectrumUsually 4000–5000 K white; fine for seedlingsWhite plus supplemental deep red and far red
Cost per foot of coverageUsually lowerUsually higher
Mounting for a shelfExcellent — designed for itDepends on form factor
DimmingRarelyCommon on panels; useful over young seedlings

What to do with a shop light you already own

Use it, and compensate for the missing specification with distance and hours rather than arithmetic:

  1. Get it close — 4 to 6 inches above the seedlings for an LED strip fixture, and raise it weekly.
  2. Run 14 to 16 hours a day. If a fixture is dimmer than ideal, hours are the lever you have.
  3. Read the plants rather than a spec sheet. Stocky green seedlings mean it is working; pale stretched ones mean lower it, lengthen the photoperiod, or add a second fixture.
  4. Prefer 4000 K or 5000 K over warm 2700 K if you are choosing. It is a small effect for seedlings, but a free one.

The verdict

If you already own a bright white LED shop light, use it — it will almost certainly do the job. If you are buying new and want to know in advance that the fixture will hit your target, buy something that publishes PPF. Paying a premium for a “grow” label on a fixture that still only publishes lumens gets you the worst of both: the price of a horticultural product and the unverifiability of a shop light.

That test — does the manufacturer publish a photon figure — is a more reliable buying filter than any brand name, and it is how our seed-starting picks are ordered.

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

Shop-light shape

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 square white LED grow panel hanging above leafy seedlings indoors
02

Spider Farmer SF1000

LED panel

Actual photon specs

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

+Can I use a regular LED shop light to start seeds?
Yes. A bright white LED shop light produces plenty of usable photons for seedlings, and gardeners have raised good transplants under them for years. The limitation is that shop lights are specified in lumens, so you cannot calculate in advance whether a given one will hit your target — you have to hang it, run it and read the plants.
+What is the difference between a shop light and a grow light?
Increasingly, mostly the specification and the price. Both are usually white LEDs. A horticultural fixture typically publishes photon output in µmol/s and often adds deep red and far red diodes; a shop light publishes lumens, which weight light by human eye sensitivity rather than by what plants use.
+How many lumens do seedlings need?
There is no honest answer, and that is the point. Lumens cannot be converted to a plant-usable figure without knowing the fixture's exact spectrum, so any lumen target is an assumption in disguise. If a fixture publishes only lumens, size it by distance and hours and judge it by how the seedlings look.

Sources

Read next

Where this sits

This page belongs to Grow Lights for Seed Starting. 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.