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Sprout & Spectrum

T5 vs T8 Grow Lights

These are tube diameters, not technologies — and most fixtures sold under both names today are LEDs in a fluorescent shape. Here is what the labels still tell you.

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

Rows of linear light fixtures mounted above plants in a growing space

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.
The T5 form factor, in LEDNot published
2
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.
Skipping tubes entirely2.7 umol/J
3
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.
When shape is not the constraint2.5 umol/J

The reasoning

This comparison is asked constantly and is, in 2026, mostly the wrong question. Here is why, in one paragraph, before the detail.

T5 and T8 are tube diameters, not technologies. The T stands for tubular and the number is the diameter in eighths of an inch: a T5 is 5/8 of an inch across, a T8 is 8/8 — a full inch. Both designations were coined for fluorescent tubes. Today the great majority of products sold as “T5 grow lights” and “T8 grow lights” are LED strips in that physical shape, which means you are frequently comparing two LEDs that differ only in how thick the housing is.

What the number in T5 and T8 actually measures
⅛ inch

T5 = 5/8 in diameter, T8 = 8/8 in. A physical dimension inherited from fluorescent tubes, carried over to LED replacements that fit the same fittings.

How to tell what you are actually buying

The wattage gives it away immediately, and it is the single most useful check on any listing in this category.

Reading the technology from the power draw on a 4 ft fixture
What you seeWhat it almost certainly isWhy
4 ft tube, around 54 WT5 HO fluorescentHigh-output fluorescent tubes of this length sit around this draw
4 ft tube, around 32 WT8 fluorescentThe standard 4 ft T8 fluorescent rating
4 ft strip, around 20 WLED, in a T5 form factorBarrina publishes 20 W per 4 ft strip — roughly a third of T5 HO fluorescent
Sold as 'T5' with no wattage at allUnknown — treat with suspicionThe wattage is the one figure that distinguishes them, so its absence is telling

The running-cost consequence of that table is substantial and is worked through in LED versus fluorescent running cost: four 4 ft tubes over a seed rack for a ten-week season come to about $44 in fluorescent and about $16 in LED.

If both are genuinely fluorescent

The comparison still means something in this case, and it is the historical answer people are half-remembering:

  • T5 HO is brighter per tube and was the standard choice for seed starting, because the higher output let you cover a tray from a fixture that could sit close.
  • T8 draws less per tube and is the older shop-light standard, generally dimmer and cheaper.
  • T5 fixtures are physically slimmer, which matters under a shelf where clearance is tight.
  • Neither publishes photon data in the consumer market, so neither can be sized arithmetically — the same problem that runs through the whole linear category.

If you already own working fluorescent tubes of either type, our view is not to replace them on efficiency grounds alone. Replace them with LED as they fail, which converts a sunk cost into a decision you were going to make anyway.

If both are LED, which is the common case

Then the diameter is close to irrelevant. What actually differs between two LED strips is what it always is: output, efficacy, length, and whether the manufacturer publishes any of it.

And here the category has a consistent problem. Barrina publishes 20 W per 4 ft strip, 5000 K, a 120-degree beam angle and a link limit of 8 fixtures — and no PPF, no PPFD and no efficacy for any strip in the range. We checked the product page directly. So the honest position on comparing two LED tube-format fixtures is that you usually cannot, on the figures that matter.

What to compare instead

The questions that actually separate linear fixtures
QuestionWhy it matters more than T5 vs T8
Does it publish PPF in µmol/s?The only figure you can divide by an area to predict what lands on your plants
How long is it?A 4 ft strip over a 4 ft shelf is the entire argument for linear fixtures. Length beats diameter
How many link in series?Barrina publishes a limit of 8, which is 160 W on one plug — this is what makes a multi-shelf rack practical
What is the power draw?Your bill tracks actual watts, and it is also how you identify the technology
How thin is the housing?Under a shelf, clearance is the binding constraint. This is the one place diameter genuinely matters

The one case where diameter still decides it

Clearance. If you are mounting under a shelf or a cabinet with 10 or 12 inches to the plants, a slimmer housing buys you usable distance. That is a real consideration and it is the legitimate remnant of the T5 versus T8 question — see the best under-cabinet grow lights.

Worth noting that the thinnest fixture we cover is not a tube at all: the AC Infinity IONBOARD S22 is a flat board 1.1 cm thick, which is slimmer than a T5 and publishes an efficacy figure a tube fixture will not give you. If clearance is the reason you were looking at T5, that board is the answer you actually wanted.

Sizing, whichever you buy

What a 4 ft shelf needs, so you can judge any fixture against it

A 4 × 1.5 ft shelf = 6 sq ft ÷ 10.7639 = 0.557 m².

For seedlings at the 12 mol/m²/day target and 14 hours a day, the required PPFD is 12 × 1,000,000 ÷ (14 × 3600) = 238 µmol/m²/s.

So PPF = 238 × 0.557 ÷ 0.8 = 166 µmol/s for the shelf.

Any fixture publishing its output can be checked against that number in one division. A fixture that publishes only a diameter and a color temperature cannot be checked against anything.

The verdict

Stop choosing on T5 versus T8 and start choosing on published output and length. If a fixture is 4 ft and links in series, it will light a shelf well regardless of which tube designation is printed on the box. If it publishes a photon figure, you can prove that before you buy — and if it does not, you are buying on shape and price, which is a reasonable decision as long as you know that is the one you are making.

For the seed-starting version of this question, including the light quality side rather than just the form factor, see T5 versus LED for seed starting.

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

The T5 form factor, in LED

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 thin aluminum LED grow board above a row of potted houseplants
02

AC Infinity IONBOARD S22

LED panel

Skipping tubes entirely

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.

A square white LED grow panel hanging above leafy seedlings indoors
03

Spider Farmer SF1000

LED panel

When shape is not the constraint

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

+What is the difference between T5 and T8 grow lights?
Tube diameter, nothing more. T is for tubular and the number is eighths of an inch, so a T5 is 5/8 in across and a T8 is a full inch. Both terms come from fluorescent tubes, and most products sold under either name today are LED strips in that physical shape.
+Is a T5 grow light fluorescent or LED?
Both exist, and the wattage tells you which you have. A 4 ft T5 HO fluorescent tube is typically around 54 W, a 4 ft T8 fluorescent around 32 W, and a 4 ft LED strip in the same form factor around 20 W — Barrina publishes exactly that figure.
+Is T5 better than T8 for growing plants?
Among genuine fluorescent tubes, T5 HO is brighter per tube and slimmer, which is why it became the seed-starting standard. Among LED strips, which is what most listings now are, the diameter barely matters — output, length and whether the manufacturer publishes any photon data matter far more.
+Should I replace my T8 fluorescent tubes with LED?
Not urgently if they work. The saving is real — four 4 ft tubes over a ten-week seed season differ by roughly $28 between fluorescent and LED — but that pays back over more than one season for most people. Replacing them as they fail is the sensible path.
+Have you tested T5 and T8 fixtures side by side?
No. We have not owned or measured any fixture on this site. The wattages above are published manufacturer figures and standard ratings for the tube types, and the sizing arithmetic is shown step by step so you can check it against whatever fixture you are considering.

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.