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Sprout & Spectrum

Grow Lights for African Violets

The plant most associated with growing under lights, sized with the same arithmetic as everything else — plus the reason a shelf of them wants a strip rather than a bulb.

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

Close-up of blooming African violet flowers in a black pot

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.
A shelf of violetsNot published
2
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.
One plant on a table1.82 umol/J (ours)
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.
A dense tray, dimmed2.7 umol/J

The reasoning

If there is one houseplant people picture growing under a lit shelf, it is the African violet. The association is old and it is earned: violets are compact, they bloom repeatedly, they resent direct sun, and they respond well to steady artificial light — which makes them one of the few houseplants that genuinely does better under a fixture than on most windowsills.

That said, the arithmetic is the same as for anything else on this site. The violet is not magic; it just sits in a band a shelf light hits easily.

Where African violets sit in the published bands
150–250

µmol/m²/s — University of Minnesota Extension's medium band. Direct sun scorches them; the bottom of the low band leaves them leafy and flowerless.

Why violets and shelves go together

Three things about the plant line up with the fixture:

  • They are small and flat. A mature violet is a rosette a few inches high. A dozen fit on a 4 ft shelf, and they all sit at the same height — which is what a linear fixture is designed for.
  • They dislike direct sun. A south window is too much; a fixture at the medium band is exactly right and never changes with the weather.
  • Flowering tracks light. A violet that has stopped blooming is usually below the band. It will keep growing leaves in low light; it will not flower there.

Sizing a violet shelf

Required PPF (µmol/s) = target PPFD × area (m²) ÷ uniformity
A 4 × 1 ft shelf of violets at 200 µmol/m²/s

Area = 4 sq ft ÷ 10.7639 = 0.372 m².

200 × 0.372 ÷ 0.8 = 93 µmol/s.

That is a modest requirement, and it is spread along a 4 ft line — which is the case for bars rather than a panel. A square panel over a 4 ft shelf lights the middle violets and starves the ones at the ends.

The geometry argument is the same as for any shelf, and it is made in full in the best grow lights for a shelf or rack.

The honest complication with bars

Barrina strips are the natural fit — 4 ft long, linkable up to 8 on one plug, 20 W each, and they run cool enough to sit close over a low plant. They are our first pick. But Barrina publishes no photon flux, no light density and no efficiency figure for any strip in the range; we checked the product page directly. So the 93 µmol/s above tells you what the shelf needs, and nothing tells you what the strips deliver.

In practice, violets tell you quickly. Two strips per shelf at 8 to 12 inches is the common starting point; if the plants go leafy and stop flowering, add a strip or drop the height. If the leaves bleach or curl, raise it. That is a slower loop than arithmetic, and for violets it works.

Placing a single bulb, computed

For one plant, SANSI publishes light density with the distance attached — 265.58 µmol/m²/s at 1 ft — which makes the bulb placeable on paper:

SANSI BR30 over one violet

At 14 in: 265.58 × (1 ÷ 1.167)² = ~195 µmol/m²/s — the top of the medium band. This is the setting we would use.

At 16 in: ~150. At 12 in: 265, which is above the band and risks scorching the fuzzy leaves.

Hours

Iowa State University Extension suggests 12 to 14 hours generally for indoor plants under supplemental light. For violets we would run 12 to 14 on a timer and keep it consistent — a regular photoperiod matters for a plant grown for its flowers.

Daily light integral at the recommended setting

195 µmol/m²/s for 13 hours: 195 × 13 × 3600 ÷ 1,000,000 = 9.1 mol/m²/day.

Comfortably inside what a medium-band plant uses, and below the seedling target of about 12 published by University of New Hampshire Extension.

The picks and their honest limits

Matched to how violets are usually kept
FixtureSuitsThe catch
Barrina T5 4ft stripsA shelf or rack of violets — the classic setupNo photon data published at all; sized by result, not in advance. No dimming; run fewer strips instead
SANSI 36W BR30One plant on a table, in a lamp you own1.82 µmol/J — a third less efficient than a panel; lights one pot
AC Infinity IONBOARD S22A dense 2 × 2 ft tray, dimmed to the medium bandSquare, so it suits a block rather than a long shelf; publishes a PPFD figure with no distance, which is unusable

Running cost

A two-strip violet shelf, all year

2 × 20 W = 40 W. 40 × 13 h ÷ 1000 = 0.52 kWh a day.

0.52 × 365 = 190 kWh a year. At 18.34 cents per kWh: $34.79 a year, or about $2.90 a month — for a whole shelf, year-round.

Signs to read

  • Leaves but no flowers: below the band. Add light or lower the fixture.
  • Leaf stems stretching upward, rosette opening out: the plant is reaching. Same fix.
  • Leaves tight, pale or bleached, curling down: too much. Raise it.
  • Crown rot, mushy center: water on the leaves or in the crown — not a light problem.

The honest summary

A shelf of violets under two linked strips at 8 to 12 inches, 13 hours a day, is the setup this plant was practically made for, and it costs about $3 a month to run. You cannot size the strips in advance because nobody publishes their output — but violets report fast, and the adjustment is a strip or an inch. For one plant on a table, the bulb at 14 inches is the placeable answer.

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

A shelf of violets

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 screw-in LED grow bulb in a desk lamp aimed at a potted houseplant
02

SANSI 36W BR30 Grow Light Bulb

Grow bulb

One plant on a table

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

AC Infinity IONBOARD S22

LED panel

A dense tray, dimmed

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 grow lights good for African violets?
Yes — they are one of the few houseplants that genuinely does better under a fixture than on most windowsills. Violets sit in the medium band of 150 to 250 µmol/m²/s, dislike direct sun, and flower in response to steady light, all of which a shelf fixture delivers and a window does not reliably.
+How far should a grow light be from African violets?
For a bulb, about 14 inches from a SANSI BR30, which scales its published 265.58 µmol/m²/s at 1 ft to roughly 195 — the top of the medium band. For linked strips over a shelf, 8 to 12 inches is the usual starting point, adjusted by whether the plants flower.
+Why won't my African violet bloom?
Most often it is below the light band. A violet keeps producing leaves in low light but will not flower there. Raising the level into the medium band, on a consistent 12 to 14 hour photoperiod, is the usual fix.
+How many hours a day for African violets?
Twelve to fourteen, on a timer. Iowa State University Extension suggests 12 to 14 hours generally for indoor plants under supplemental light, and consistency matters more for a plant grown for flowers than for a foliage plant.
+Have you grown African violets under these lights?
No. We have not owned or measured any fixture on this site and have grown nothing under them. Every figure here is published by the manufacturer or an extension service with a link, or computed from those figures with the arithmetic shown.

Sources

Read next

Where this sits

This page belongs to Grow Lights for Houseplants and Winter. 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.