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Sprout & Spectrum

The Best Grow Light Bulbs

Screw-in fixtures do one job well. Here is the job, the efficiency you pay for it, and the one bulb whose placement you can compute in advance.

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 desk lamp beside a small potted plant in a bright room

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
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.
The one with real data1.82 umol/J (ours)
2
A gooseneck clip-on grow light clamped to a shelf beside a small houseplant
GooingTop Clip Grow Light
The cheapest way to put real light on one plant on one desk, and honest about being exactly that — a 10 W clip lamp with a repeating timer.
No socket requiredNot published
3
A pendant grow light hanging over a large indoor plant in a living room
Soltech Aspect Gen 2
The only fixture here you would willingly hang in a living room, and the only one publishing PPFD at three separate distances so it can actually be placed by the numbers.
A fitting, not a bulb1.39 umol/J (ours)

The reasoning

A grow bulb is the right answer to a narrow question: you have one plant, you have a lamp, and you do not want to mount a fixture. Within that description it is genuinely the best tool. Outside it, the economics turn against you fast.

What the form factor costs

Efficacy of the screw-in form factor, computed

SANSI 36W BR30: 65.6 µmol/s ÷ 36 W = 1.82 µmol/J.

Soltech Aspect Gen 2 (a pendant rather than a bulb, but the same compact-fixture constraint): 50 ÷ 36 = 1.39 µmol/J.

Panels in the same catalog publish 2.3 to 2.75 µmol/J. So the compact form factors run roughly a third to a half less efficient.

The reason is physical: a bulb has almost no surface for heat sinking and has to fit an E26 socket. Panels are wide flat aluminum for exactly that reason.

Efficiency penalty of a screw-in bulb against a panel
~34%

1.82 µmol/J against 2.75. You are paying that penalty in exchange for using a lamp you already own and not mounting anything.

The one that publishes enough to place

SANSI publishes 65.6 µmol/s and — the important one — 265.58 µmol/m²/s at a stated 1 ft. That distance is what makes the figure usable, and it makes this the only bulb we cover whose placement can be worked out on paper.

What the SANSI bulb delivers at various heights, scaled by the inverse-square relationship from its published 1 ft figure
DistancePPFD (µmol/m²/s)Band
6 in~1,062Far above the published bands
9 in~472Above the high band
12 in265.58 (published)High
15 in~170Medium
18 in~118Low
24 in~66Low, near the floor

Read down to the band your plant wants — the targets are in PPFD targets by plant type — and you have your lamp height before you have bought anything. That is not possible with any other bulb we found.

When a bulb stops making sense

Roughly at the second plant. 65.6 µmol/s spread into a cone serves one specimen properly. Two plants means either two bulbs and two lamps, or one bulb hung higher over both — at which point the inverse-square relationship has cut the intensity to a fraction.

By the third or fourth bulb you have spent more than a panel would have cost and you are running at two-thirds the efficiency. The crossover is earlier than most people expect.

The alternatives at the same scale

  • No socket available? A clip light. The GooingTop clamps anywhere, draws about 10 W and has a repeating timer built in. Nobody publishes photon data for it, so it cannot be placed by arithmetic — see the clip light write-up.
  • Somewhere people will see it? A pendant. The Soltech Aspect is a light fitting that grows plants rather than a grow light you tolerate, and it publishes PPFD at three distances.
  • More than one plant? Stop looking at bulbs. A panel or a strip is cheaper and more efficient from roughly the second plant onward.

Running cost

36 W at 12 hours a day is 12.96 kWh a month, about $2.38 at the US residential average, or roughly $14.42 across an October-to-March winter. At that level the efficiency penalty is real in principle and negligible in dollars — which is exactly why the form factor survives.

Every pick in full

A screw-in LED grow bulb in a desk lamp aimed at a potted houseplant
01

SANSI 36W BR30 Grow Light Bulb

Grow bulb

The one with real data

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 gooseneck clip-on grow light clamped to a shelf beside a small houseplant
02

GooingTop Clip Grow Light

Clip light

No socket required

The cheapest way to put real light on one plant on one desk, and honest about being exactly that — a 10 W clip lamp with a repeating timer.

What GooingTop publishes

Power draw
About 10 W (source)
Spectrum
6000 K, 74 white plus 10 red LEDs, CRI 95 (source)
Dimming
Five brightness levels; repeating 4 / 8 / 12 hour timer (source)

What GooingTop does not publish

  • PPF in umol/s
  • PPFD at any distance
  • Photon efficacy in umol/J
  • The manufacturer publishes no spec sheet at all; the figures above come from the retail listing

Who should skip it

Skip it if the plant is more than about a foot across, or if you want any number at all before you buy — nobody publishes photon data for this fixture.

A pendant grow light hanging over a large indoor plant in a living room
03

Soltech Aspect Gen 2

Pendant

A fitting, not a bulb

The only fixture here you would willingly hang in a living room, and the only one publishing PPFD at three separate distances so it can actually be placed by the numbers.

What Soltech publishes

Power draw
36 W (source)
PPF (photon output)
50 umol/s (source)
PPFD
about 50 umol/m2/s at 1 m, 34.9 at 4 ft, 15.5 at 6 ft (source)
Spectrum
3000 K warm white, CRI 98 (source)
Dimming
Yes, in-line dimmer 10-100% (source)
Dimensions
3.5 x 3.5 x 6.2 inches (source)
Rated life
50,000 hours (source)

Our arithmetic

  • Efficacy, computed from the published figures: 1.39 umol/J
    50 umol/s / 36 W = 1.39 umol/J. Roughly half the efficacy of a 2.7 umol/J board — the design premium is paid twice, once at purchase and again every month on the meter.

Who should skip it

Skip it if photons per watt is the metric that matters. At 50 umol/s from 36 W it is the least efficient fixture on this page, and much of the price is industrial design.

Questions people actually ask

+Do grow light bulbs actually work?
For one plant at close range, yes. The SANSI BR30 publishes 65.6 µmol/s and 265.58 µmol/m²/s at a stated one foot, which is a high light level for a single specimen. Spread that same output over a shelf and it becomes negligible.
+How far should a grow bulb be from a plant?
Scaling the SANSI bulb's published figure by the inverse-square relationship: about 12 inches for a high light level, 15 for medium, and 18 for low. Pick from the target your plant actually wants rather than from a general rule.
+Is a grow bulb worth it compared to a panel?
For a single plant beside a lamp you already own, yes — you skip mounting entirely. Per watt it is roughly a third less efficient than a panel, but at 36 W and about $2.38 a month, that penalty costs pennies. From the second or third plant on, a panel wins clearly.
+Can I use a grow bulb in a normal lamp?
That is the whole point of the form factor. The SANSI is a BR30 in an E26 socket, which is a standard fitting. Check the lamp's maximum rated wattage, though 36 W is inside almost any modern fixture's limit.

Sources

Read next

Where this sits

This page belongs to Fixture Reviews and Roundups. 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.