Grow Lights
The Best Grow Light Bulbs for Indoor Plants
This is the one corner of plant lighting where manufacturers actually print the photon numbers. Here is how to read them, and who does not.
By Scooter M., enthusiast · Published
The short answer
Buy the bulb that publishes a photon figure with the distance it was measured at, because in this category some of them genuinely do. One bulb here states PPF 65.6 umol/s and PPFD 265.58 umol/m2/s at 1 ft; another states 1300 umol/m2/s at 6 in. A third publishes 1000 lumens, which measures what your eye sees rather than what the plant uses. Screw-in bulbs suit one plant at a time — they throw a cone — so if you are lighting a shelf you want linkable bars instead.
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This site has been mildly annoyed about plant light specifications for a while. The Barrina review spends several paragraphs on a bar that advertises "High PPFD" and then declines to publish a PPFD. It is the standard behavior of the category.
Screw-in bulbs, it turns out, are the exception. Two of the three new bulbs on this page print a photon figure and the distance it was measured at. That is a checkable specification, and it changes what this page can do.
The three units, and which one is about plants
| Unit | What it measures | Is it about plants? |
|---|---|---|
| Watts | Electricity consumed | No — an input, not an output |
| Lumens | Brightness as the human eye perceives it | No — weighted to green, which plants reflect |
| PPF (umol/s) | Total photons the fixture emits | Yes — the honest output figure |
| PPFD (umol/m2/s) | Photons landing on a square meter | Yes — but only at the stated distance |
| Kelvin | Color temperature, how white it looks | Indirectly — decides if you can live with it |
Lumens is the trap. It is a real measurement and it is weighted by the sensitivity of the human eye, which peaks in green — the part of the spectrum plants reflect rather than absorb. A bulb can be high in lumens and modest in photons. One bulb here publishes 1000 lm and no photon figure, which is better than an adjective and not comparable with the two that print PPFD.
What you can compute from published figures
PPF / watts = umol/J; PPFD x (d1/d2)^2 = PPFD at a new distance; PPFD x seconds / 1,000,000 = mol/m2/day
65.6 umol/s / 36 W = 1.82 umol/J. SANSI's own 10 W bulb publishes 16.8 umol/s, deriving to 1.68 umol/J. A PPFD of 1300 at 6 in, treated as a point source, is about 325 at 1 ft. A PPFD of 265.58 running 12 hours is 265.58 x 43,200 / 1,000,000 = about 11.5 mol/m2/day.
All three are DERIVED from manufacturer figures, not quoted. The inverse-square step is an approximation — a PAR38 reflector is not a point source, and treating it as one flatters a narrow beam. The daily light figure applies to the spot directly under the bulb, not to the whole plant.
Efficacy is the most useful of those and the one nobody prints. Photons per joule tells you how much light you get per unit of electricity, and it lets you compare a 36 W bulb with a 10 W one on something other than size. Here the bigger bulb is modestly the more efficient, which is not a given.
A bulb throws a cone. A bar throws a line.
This is the shape question, and it decides whether a bulb is the right product at all. A screw-in bulb radiates from a point into a cone — bright in the middle, falling off toward the edges. A linkable bar spreads the same watts along a row.
That makes a bulb excellent at lighting one plant well and poor at lighting a shelf evenly. It is the same arithmetic the Barrina review lays out from the other side: four 1-foot bars publish 20 W in total, about 5 W per foot, which is a supplement across a wide area. A single 36 W bulb is nearly twice that power aimed at one plant.
| You want to light | Use | Why |
|---|---|---|
| One floor plant in a dark corner | A bulb, in a lamp you own | A cone aimed at one plant is what a bulb does |
| A shelf of small pots | Linkable bars | Even light along a row; a bulb makes a bright middle |
| A tall plant from above | PAR38 reflector bulb | Concentrates photons and reaches further down |
| Seedling trays | Bars, mounted close | Flat even coverage at two inches |
| Several lamps around a room | A multipack of A19 bulbs | Cheapest conversion of fixtures you already have |
The fixture you screw it into matters
- E26 is the standard US base and every bulb here uses it, so they fit ordinary lamps, pendants and clamp fixtures without an adapter.
- Check the fixture's wattage limit. A 36 W LED draws far less than the incandescent bulbs old fixtures were rated for, so this is rarely a problem — but a fully enclosed shade traps heat, and heat is what shortens LED life.
- A PAR38 face is 4.7 inches across. That will not fit every shade or every clamp reflector. Measure before buying the reflector format.
- Aim matters more than with a bar. A bulb pointing at a ceiling is lighting the ceiling. A gooseneck or clamp fixture that lets you aim it at the plant is worth more than a slightly better bulb in a fixed lamp.
- Put it on a timer. A plug-in timer costs less than the bulb and is the cheapest improvement to any lit setup.
Quick picks
Ranked, with the published figure each pick turns on. Tap a row for the full reasoning further down this page.
| # | Product | Best for | Price |
|---|---|---|---|
| 1 |  SANSI LED Grow Light Bulb, 36 W, E26, 4000 KPublishes photosynthetic photon flux, photon flux density and the distance it was measured at — three things most of the lighting on this site does not print at all. | One plant that needs real light, from the only listing that prints both photon numbers | $33.26 at Amazon $39.95 · 17% off |
| 2 |  Lonwon PAR38 Grow Light Bulb, 30 W, E26, 4000 KThe highest published photon density here by a distance — in a reflector format that concentrates it into a narrower cone, which is the trade nobody spells out. | Concentrating light on one tall plant from further away | $25.99 at Amazon $32.99 · 21% off |
| 3 |  Briignite A19 Grow Light Bulbs, 4 pack, E26, 4000 KThe cheapest way to convert existing lamps into plant lights — and the clearest example on this page of a listing publishing the wrong unit. | Putting a grow bulb in four lamps you already own, cheaply | $16.99 at Amazon $18.99 · 11% off |
| 4 |  Briignite A19 Full Spectrum Grow Light Bulb, 11 W, 5000 KAn ordinary-looking A19 bulb with a published PPF, sold at a price that makes it the cheapest experiment in this section. | The cheapest way to find out whether a plant wants more light | |
| 5 |  Barrina Clip On Grow Light, 22 W, 4000 KPublishes both its wattage and its color temperature, and clips to a shelf edge. The smallest useful intervention in this entire section. | One plant that needs more light than its corner gives | $25.99 at Amazon $32.99 · 21% off |
Links to Amazon are affiliate links. Prices and availability are Amazon's and change without notice.
How we ranked these
On whether photon figures are published at all, then on whether a measurement distance came with them, then on what the format is good for. The 36 W SANSI leads on a clean sweep of the specification question: PPF, PPFD and the distance, which lets you derive efficacy and daily light without guessing at anything. The PAR38 is second with the highest published density here, marked down only because quoting it at 6 inches flatters it against a bulb quoted at a foot, and because a reflector trades coverage for that intensity. The A19 four-pack is third and is the value purchase — four existing lamps converted — with the honest note that lumens is the wrong unit for the job. The existing 11 W A19 follows as the single-bulb version of the same idea. The clip light is last and is not a bulb at all: it is on the page because for one plant on a shelf edge, a 22 W clip light with its own arm often beats finding a lamp to put a bulb in.
What we deliberately do not recommend
Comparing two PPFD figures quoted at different distances, which is a factor of four in this set alone. Reading lumens as a plant-light specification. Buying a bulb to light a shelf evenly, which is a job for bars. Putting a reflector bulb in a fully enclosed shade. Taking a PPFD or daily-light target from a website that does not say where it got it — including the derivation on this page, which compares products and does not prescribe. And buying any of these without a timer, since an erratic photoperiod undoes most of what the light is for.
Every pick, in full
We have not handled any of these. What follows is what each listing publishes, what that means once you put a watered pot on it, and who should buy something else.
1. One plant that needs real light, from the only listing that prints both photon numbers
SANSI LED Grow Light Bulb, 36 W, E26, 4000 K
Publishes photosynthetic photon flux, photon flux density and the distance it was measured at — three things most of the lighting on this site does not print at all.
- What the listing publishes
- Published PPF 65.6 umol/s and PPFD 265.58 umol/m2/s measured at 1 ft; 36 W at 4000 K covering a stated 400-780 nm; stated Chip-on-Ceramic construction with a ceramic heat sink rather than an aluminum substrate; stated flame-retardant V0 body; ETL listed with a stated 5-year protection plan
- Against a 10-inch pot
- No weight rating is published for this product, so there is nothing to check. That counts against it here rather than being treated as neutral.
PPF and PPFD with a stated distance is the specification that makes a plant light checkable. PPF, 65.6 umol/s, is the total photon output of the bulb. PPFD, 265.58 umol/m2/s at 1 ft, is what actually lands on a square meter directly underneath. Publishing both with a measurement distance is rare enough in this category to be the reason this leads.
It also lets you compute efficacy, which nothing on a box ever shows you: 65.6 umol/s divided by 36 W is about 1.82 umol per joule. SANSI publishes 16.8 umol/s for its own 10 W bulb, which derives to 1.68 umol/J — so the bigger bulb is modestly more efficient per watt as well as brighter, and both figures come from the manufacturer rather than from us.
Ceramic rather than aluminum is a heat-path claim, and heat is what kills LED output over years. It is not something a buyer can verify, but it is at least a statement about construction rather than an adjective about brightness.
What is good
- Publishes PPF, PPFD and the distance PPFD was measured at
- Enough published output to be one plant's main light source
- ETL listed with a stated 5-year protection plan
What is not
- Most expensive bulb here by a wide margin
- 36 W in a table lamp is a lot of light to sit beside in the evening
- PPFD is a figure directly underneath; it falls off steeply toward the edges
Skip it if you are lighting a shelf rather than a plant. A bulb throws a cone; linkable bars spread the same watts along a row, which is a different job.
2. Concentrating light on one tall plant from further away
Lonwon PAR38 Grow Light Bulb, 30 W, E26, 4000 K
The highest published photon density here by a distance — in a reflector format that concentrates it into a narrower cone, which is the trade nobody spells out.
- What the listing publishes
- Published PPFD of 1300 umol/m2/s at 6 in; 30 W PAR38 format with a stated 184 LEDs and a 4.7 in face; stated 4000 K with enhanced 660 nm and 730 nm wavelengths; E26 base
- Against a 10-inch pot
- No weight rating is published for this product, so there is nothing to check. That counts against it here rather than being treated as neutral.
Thirteen hundred umol/m2/s at 6 inches is a big number, and the distance it is quoted at is the reason. Treating the bulb as a point source and stepping back to a foot, the inverse-square rule puts it near 325 umol/m2/s — a derived figure, and an approximation, because a PAR38 reflector is not a point source. It is still the right order of magnitude for comparing against a bulb quoted at 1 ft.
PAR38 is a reflector format: a wide glass face with the light aimed forward into a cone. That is why the density is high. It also means the lit area is narrower than an omnidirectional bulb of the same wattage, so you are trading coverage for intensity and the listing does not frame it that way.
Enhanced 660 nm and 730 nm is a specific spectral claim rather than "full spectrum", which counts for something — those are named wavelengths rather than a marketing phrase. No spectral distribution chart is published to check it against.
What is good
- Publishes a PPFD figure with the distance it was taken at
- Reflector format puts more photons on a small target
- Names specific wavelengths rather than only "full spectrum"
What is not
- Reflector concentrates, so the lit area is narrower than the number suggests
- PPFD quoted at 6 in, which flatters it against bulbs quoted at 1 ft
- A 4.7 in face will not fit every shade or fixture
Skip it if the plant is wide rather than tall. A cone of light over a spreading plant lights the middle and leaves the edges out.
3. Putting a grow bulb in four lamps you already own, cheaply
Briignite A19 Grow Light Bulbs, 4 pack, E26, 4000 K
The cheapest way to convert existing lamps into plant lights — and the clearest example on this page of a listing publishing the wrong unit.
- What the listing publishes
- Published 1000 lm output across a stated 180 degree spread; A19 format on an E26 base, stated 4000 K white with a red and blue spectrum; stated equivalent to a 100 W traditional bulb; 4 bulbs per pack; no PPF or PPFD figure published
- Against a 10-inch pot
- No weight rating is published for this product, so there is nothing to check. That counts against it here rather than being treated as neutral.
A thousand lumens is a real, measured figure and it is not a plant measurement. Lumens weight light by how bright the human eye perceives it, which peaks in the green that plants reflect. A bulb can be high in lumens and modest in photons, or the reverse. It is better than an adjective and it is not comparable with the PPFD figures elsewhere on this page.
Four bulbs is the actual argument. An A19 in an E26 base fits essentially every table lamp, floor lamp and pendant in a US home, so four bulbs is four existing fixtures converted for the price of one purpose-built bulb.
"Equivalent to 100 W traditional" is an energy-consumption comparison, not a plant-light claim, and it should not be read as one. It tells you about your electricity bill.
What is good
- Four bulbs, so several existing lamps become plant lights at once
- Publishes a lumen figure and a beam spread, unlike most of this category
- 4000 K white rather than a magenta glow in a living room
What is not
- No PPF or PPFD published, so it cannot be compared on photons
- Lumens measure what the eye sees, not what the plant uses
- 180 degree spread means a lot of the light goes where no plant is
Skip it if you want to know what the plant is receiving. Two bulbs on this page publish photon figures and this one publishes a brightness figure.
4. The cheapest way to find out whether a plant wants more light
Briignite A19 Full Spectrum Grow Light Bulb, 11 W, 5000 K
An ordinary-looking A19 bulb with a published PPF, sold at a price that makes it the cheapest experiment in this section.
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- What the listing publishes
- Published 11 W A19, 5000 K white; 1000 lumens; PPF stated at 25 umol/s; stated 25,000 hour life
- Against a 10-inch pot
- No weight rating is published for this product, so there is nothing to check. That counts against it here rather than being treated as neutral.
A lot of grow-light shopping is really a diagnosis: is the plant struggling because of light or because of something else? An 11 W bulb in an existing lamp answers that for less than the cost of a takeout order, and if the answer is yes, the next purchase is a bar set with a clearer conscience.
The listing publishes 25 umol/s of PPF, which is more than the SANSI bulb's 16.8 — but it does not publish a PPFD at any distance, so how much of that reaches a leaf depends entirely on the lamp it is in and how close the plant sits.
5000 K is cooler and whiter than 4000 K. In a bedroom lamp it looks like daylight rather than lamplight, which some people want and some do not.
What is good
- Publishes PPF, which most bulbs at this price do not
- Standard A19 shape fits lamps a grow bulb usually will not
- Low enough cost to be a diagnostic rather than a commitment
What is not
- No published PPFD at any distance, so real delivery is unknown
- 5000 K reads as clinical in a warm-lit room
- Marketed at vegetables — useful for houseplants, but the listing is not written for them
Skip it if the plant is a succulent or a cactus. 11 W in a lamp is a low-light fix, and sun plants need the clip or bar options rather than a bulb.
5. One plant that needs more light than its corner gives
Barrina Clip On Grow Light, 22 W, 4000 K
Publishes both its wattage and its color temperature, and clips to a shelf edge. The smallest useful intervention in this entire section.
- What the listing publishes
- Published 22 W (2 by 11 W) at 4000 K; clip mount
- Against a 10-inch pot
- No weight rating is published for this product, so there is nothing to check. That counts against it here rather than being treated as neutral.
22 W on one plant is a genuinely useful amount of light. The same 22 W spread across a six-tier shelf would be nothing, which is why per-plant clip lights outperform their wattage.
4000 K is warmer than the 5000 K bars and noticeably less clinical in a living room, at a small cost in usable output for the plant.
A clip needs something to clip to, with a lip. Shelf edges work; a windowsill usually does not.
What is good
- Publishes watts and color temperature
- 22 W concentrated on one plant does real work
- No mounting, no fixing, and it moves with the plant
What is not
- Needs a shelf edge or similar to clip to
- Lights one plant, not a collection
- Two heads means two points of aim to get right
Skip it if you have a whole shelf to light. Clip lights do not scale, and a linkable bar set is the right tool at that point.
Questions people actually ask
Do grow light bulbs actually work?
What is PPFD and why does it matter for a grow bulb?
Are lumens a good measure for a grow light?
Grow light bulb or grow light bar?
What wattage grow light bulb do I need?
Will a grow light bulb fit a normal lamp?
What color temperature should a grow bulb be?
Sources
- University of Illinois Extension: Houseplants — lighting
- University of Georgia Extension B1318: Growing Indoor Plants with Success
- Michigan State University Extension: Smart Gardening — growing houseplants indoors
Product specifications are quoted from each seller's own listing and are the seller's claim, not a measurement of ours.