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Sprout & Spectrum

Bar vs Panel Coverage and Uniformity

The same photons, distributed two different ways. The right choice is decided by the shape of your shelf, not by the brand on the box.

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 LED light strip glowing against a dark background

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.
Long, shallow shelvesNot 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.
Square footprints2.5 umol/J
3
A thin aluminum LED grow board above a row of potted houseplants
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.
Flat mounting2.7 umol/J

The reasoning

Two fixtures can emit the same number of photons per second and produce completely different results, because distribution is a separate property from output. This is the part of grow-light selection that a photons-per-area calculation deliberately averages away, and it is worth understanding before you spend anything.

What each form factor physically does

A panel concentrates its emitters into a compact rectangle, usually around 30 cm square for the 100 W class. All the light originates from that small region and spreads outward in a cone, so intensity is highest directly underneath and falls off toward the edges of the footprint.

A bar distributes its emitters along a line, typically 4 ft. Light originates all along that line, so the intensity profile is roughly even along the length of the bar and falls off across the width. Multiple bars spaced across an area approximate an evenly lit plane.

Distribution properties of the two form factors
PropertyPanelBar
Source geometryCompact, roughly a pointLinear, along 4 ft
Intensity profilePeaks in the center, falls toward the edgesEven along the length, falls across the width
Best-suited shapeSquare footprints of similar dimension to the panelLong, shallow rectangles
MountingHangs; needs a crossbar or ceiling hookScrews or ties flat under a shelf
ScalingAdd another panel; distribution stays lumpyAdd another bar; distribution improves
Typical dimmingUsually included on the 100 W classOften none; you run fewer strips instead

The geometry argument, in numbers

Why a square panel wastes output on a long shelf

Take a 4 × 1.5 ft shelf: 6 sq ft, 0.557 m².

A panel with a published 2 × 2 ft footprint covers 4 sq ft. Even perfectly centered, roughly a third of the shelf area sits outside its stated footprint, while part of its footprint spills off the front and back edges of a 1.5 ft-deep shelf.

Two 4 ft bars laid along the shelf put emitters over the whole 4 ft length. Every point on the shelf is under a run of diodes.

The area-average calculation reports the same PPFD in both cases. Your plants at the ends of the shelf report something very different.

Where panels genuinely win

  • Square areas. A 2 × 2 ft block of pots is exactly what a 2 × 2 ft panel is designed for, and a bar arrangement there is fussier for no benefit.
  • Height available. A panel hung 18 inches up spreads into a much wider, more even footprint. If you have the headroom, the uniformity problem shrinks considerably.
  • Published data. This is the underrated one. Panels from the brands we cover publish photon output; the dominant bar product does not. Buying a panel means you can compute what you will get.
  • Dimming. Panels in this class almost all dim. Bars mostly do not.

Where bars genuinely win

  • Shelves and racks. The shape matches, and they mount flat underneath without hanging hardware. See the best grow lights for a shelf or rack.
  • Low clearance. Under a shelf you may have 10 inches total. A bar works at that height; a panel produces a hotspot.
  • Seed trays. Trays are long rectangles and seedlings want the light close, which is precisely the bar case. Covered in the shelf setup for seed trays.
  • Cost per square foot. Linked strips are the cheapest way to light a length of shelf, by a wide margin.

The honest summary

Measure the area you are lighting. If its longest side is more than about twice its shortest, buy bars. If it is roughly square, buy a panel. If you need to know exactly what you are getting before it arrives, buy a panel regardless, because that is where the published data is.

Whichever way you go, size it in the coverage calculator and remember that the uniformity factor in that sum is an assumption — it is precisely this distribution question wrapped up in a single number.

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

Long, shallow shelves

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

Square footprints

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.

A thin aluminum LED grow board above a row of potted houseplants
03

AC Infinity IONBOARD S22

LED panel

Flat mounting

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.

Questions people actually ask

+Are LED grow light bars better than panels?
For long, shallow areas like shelves and seed trays, yes, because their emitters run along the shape you are lighting. For square footprints a panel is the better match. Neither is better in the abstract; the shape of your growing area decides it.
+Do bars give more even coverage?
Along their length, clearly. Several bars spaced across an area approximate an evenly lit plane far better than one panel of equivalent output, which concentrates its light at a point and falls off toward the edges.
+Can I mix bars and panels?
Yes, and it is often the practical answer on a multi-shelf rack: bars where clearance is tight, a panel where one shelf holds a dense square block of plants. Photons add regardless of the fixture that emitted them.
+Why do bars usually cost less?
Simpler construction, no heat sink of any size, no driver housing, no dimming circuit, and passive cooling. It also means fewer published specifications, which is the trade-off you accept for the lower price.

Sources

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Where this sits

This page belongs to Coverage and Sizing Math. 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.