The Best Grow Lights for Seed Starting
Five fixtures, each sized against a published target rather than a marketing claim — plus the one that everybody buys and nobody can verify.
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
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.
| # | Product | Best for | Efficacy | Price |
|---|---|---|---|---|
| 1 |  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. | Whole shelves of trays | Not published | |
| 2 |  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. | One tray, verifiable | 2.5 umol/J | |
| 3 |  Mars Hydro TS 1000 The most photons of anything on this list, and one of only three fixtures here that publishes both PPF and efficacy so the claim can be checked against itself. | Most photons | 2.3 umol/J | |
| 4 |  AC Infinity IONBOARD S22 The highest published efficacy of any fixture here at 2.7 umol/J, on Samsung LM301H diodes, with dimming in real 20% steps rather than a vague knob. | Lowest running cost | 2.7 umol/J | |
| 5 |  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. | A single pot | 1.82 umol/J (ours) |
The reasoning
Seedlings are the least forgiving thing you can put under a light. Give a pothos too little and it sulks for a month; give a tomato seedling too little and it stretches into a pale, floppy stem within four days and never fully recovers. So the question “which grow light for seed starting” has an actual right answer, and it starts with a number rather than a product.
The University of New Hampshire Extension puts the target plainly: seedlings want about 12 moles of light per square meter per day. That is a daily light integral (DLI), and it is the figure every pick below is sized against.
Daily light integral for seedlings, per University of New Hampshire Extension. Everything below is an attempt to hit that number over a specific area, for a specific number of hours.
How we picked
We have not tested any of these fixtures. What we did instead was find every photon figure each manufacturer publishes, divide it against the area it claims to cover, and check the result against the 12 mol target at a realistic photoperiod. Three rules governed the list:
- A published PPF beats a big number on the box. PPF is photons per second out of the fixture, in µmol/s. It is the only figure you can divide by an area, and roughly half of the popular seed-starting lights do not publish it at all.
- Efficacy decides the running cost. Photons per joule (µmol/J) is how much of your electricity becomes usable light. Across this list it ranges from 1.39 to 2.7 — nearly a factor of two on the same bill.
- Form factor has to match the shelf. A 2 × 2 ft panel over a 4 ft tray wastes half its output on the edges. Bars beat panels for trays; panels beat bars for a single dense block.
The full method, including the formulas, is on our methodology page. Everything in the table above is either quoted from a manufacturer or divided out in view.
Sizing a seed-starting light in one division
You do not need a light meter to work out whether a fixture will do. You need its PPF, the area you are lighting, and the number of hours you plan to run it.
DLI (mol/m²/day) = PPFD × hours × 3600 ÷ 1,000,000
The SF1000 publishes 249.21 µmol/s. A standard 1020 seed tray is about 11 × 21 inches, so 1.6 sq ft, or 0.149 m².
249.21 ÷ 0.149 = 1,672 µmol/m²/s at perfect uniformity. That is far more than a seedling needs, which is the useful finding: hang it higher and spread it over four trays instead of one.
Over four trays (6.4 sq ft, 0.595 m²) at a 0.8 uniformity factor: 249.21 ÷ 0.595 × 0.8 = 335 µmol/m²/s. At 14 hours a day, DLI = 335 × 14 × 3600 ÷ 1,000,000 = 16.9 mol/m²/day — comfortably past the 12 mol target, with margin for the corners.
Run your own numbers in the coverage calculator, which does exactly this arithmetic and shows its working.
Bars or panels?
This is the decision that actually matters for seed starting, and it is decided by the shape of your shelf, not by the brand.
| Setup | Better form factor | Why |
|---|---|---|
| One or two 1020 trays on a shelf | Linked LED bars | A 4 ft bar matches a 4 ft shelf. A square panel over a long tray dumps most of its output past the ends. |
| A dense 2 × 2 ft block of pots | LED panel | Square output over a square area. This is the geometry panels are designed for. |
| A three-shelf rack of trays | Bars, one run per shelf | Panels cannot be mounted close enough under a shelf without hot spots and shadowed corners. |
| One pot on a desk | Grow bulb or clip light | A 249 µmol/s panel over one pot is 90% waste, and you still pay for it. |
What we could not tell you
The most-purchased seed-starting light in this category is also the one we can say least about. Barrina publishes no PPF, no PPFD and no efficacy figure for any strip in its T5 range — we checked the product pages directly. It is still our first pick for whole shelves, because the form factor is right and the price per linear foot is unbeatable, but you should buy it knowing that nothing about its light output can be verified in advance. That is not a criticism of the hardware; it is a statement about what is knowable.
If you want a fixture whose output you can check before you buy, the SF1000 is the one on this list that publishes both PPF and efficacy, and whose two figures agree when you divide them.
How much will running it cost?
Less than people expect. A 160 W string of eight linked bars, run 16 hours a day for the eight weeks of a typical seed-starting season, at the US residential average of 18.34 cents per kWh:
160 W × 16 h ÷ 1000 = 2.56 kWh a day.
2.56 × 56 days = 143.4 kWh for the season.
143.4 × $0.1834 = about $26 for the whole run.
Work it out for your own fixture and tariff with the running-cost calculator, or read how much electricity grow lights actually use.
Every pick in full
Barrina T5 4ft Grow Light Strips
LED barWhole shelves of trays
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.
Spider Farmer SF1000
LED panelOne tray, verifiable
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.
Mars Hydro TS 1000
LED panelMost photons
The most photons of anything on this list, and one of only three fixtures here that publishes both PPF and efficacy so the claim can be checked against itself.
What Mars Hydro publishes
- Power draw
- 150 W +/-5% at 100-277 V AC (source)
- PPF (photon output)
- 343 umol/s (source)
- Efficacy
- 2.3 umol/J (source)
- Stated coverage
- 2.5 x 2.5 ft vegetative, 2.3 x 2.3 ft flowering (source)
- Spectrum
- 660-665 nm, 730-740 nm, 3000 K, 5000 K (source)
- Diodes
- Bridgelux (source)
- Dimming
- Yes, 0-100% dimmer knob (source)
- Dimensions
- 406 x 326 x 50 mm (source)
Our arithmetic
- Average PPFD across its stated 2.5 x 2.5 ft vegetative footprint: about 470 umol/m2/s
2.5 ft x 2.5 ft = 6.25 sq ft = 0.581 m2. 343 umol/s divided by 0.581 m2 = 590 umol/m2/s at perfect uniformity; applying a 0.8 uniformity factor gives about 472 umol/m2/s average. - Electricity used at 14 hours a day for 30 days: 63.0 kWh a month
150 W x 14 h x 30 d / 1000 = 63.0 kWh.
Who should skip it
Skip it if you are lighting a bookshelf. 343 umol/s concentrated into a 2.5 ft square is far more light than a monstera wants, and you pay 150 W to deliver it.
AC Infinity IONBOARD S22
LED panelLowest running cost
The highest published efficacy of any fixture here at 2.7 umol/J, on Samsung LM301H diodes, with dimming in real 20% steps rather than a vague knob.
What AC Infinity publishes
- Power draw
- 115 W (source)
- Efficacy
- 2.7 umol/J (source)
- PPFD
- 1098 PPFD (no measurement distance published) (source)
- Stated coverage
- 2 x 2 ft (source)
- Spectrum
- Samsung LM301H, plus 660 nm, 730 nm, 3000 K, 6500 K (source)
- Diodes
- 272 diodes (source)
- Dimming
- Yes, 0-100% in 20% increments (source)
- Dimensions
- 30.0 x 30.0 cm board, 1.1 cm thick (source)
- Rated life
- 50,000 hours (source)
Our arithmetic
- Photon output implied by the published wattage and efficacy: about 311 umol/s
115 W x 2.7 umol/J = 310.5 umol/s. AC Infinity does not print PPF directly, so this is our arithmetic from two figures it does print.
What AC Infinity does not publish
- PPF in umol/s — only efficacy is given, so photon output has to be derived
- The measurement distance for the 1098 PPFD figure, without which the number cannot be compared to anything
Who should skip it
Skip it if you want to place it by the numbers. AC Infinity prints 1098 PPFD with no measurement distance attached, which makes that figure impossible to use or compare.
SANSI 36W BR30 Grow Light Bulb
Grow bulbA single pot
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.
Questions people actually ask
+How many hours a day should a seed-starting light be on?
+Do I need a special grow light, or will a shop light work?
+Is more light always better for seedlings?
+Have you tested these lights?
Sources
- University of New Hampshire Extension — Growing Seedlings Under Lights — consulted September 2, 2026
- University of Minnesota Extension — Lighting for indoor plants and starting seeds — consulted September 2, 2026
- Iowa State University Extension — Important Considerations for Providing Supplemental Light to Indoor Plants — consulted September 2, 2026
- Virginia Cooperative Extension — Calculating and Using Daily Light Integral (DLI), SPES-720 — consulted September 2, 2026
- Spider Farmer — SF1000 published specification table — consulted September 2, 2026
- Barrina — T5 ML20 4ft 20W product page — consulted September 2, 2026
- US Energy Information Administration — Electric Power Monthly, Table 5.3 (US residential average, June 2026) — consulted September 2, 2026
Read next
Seed Starting
How Far Should Grow Lights Be From Seedlings?
Distance by fixture type, in a table, with the inverse-square arithmetic that explains why an inch matters so much.
Seed Starting
How Much Light Do Seedlings Actually Need?
The 12 mol/m2/day seedling target, converted into the PPFD and hours you can actually set.
Coverage & Sizing
Grow Light Coverage Calculator
Put in PPF, area and hours; get PPFD and DLI scored against published extension bands.
Running Cost
The Most Efficient Grow Lights by µmol/J
Every fixture we cover ranked on published photon efficacy, with derivations shown.
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.