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Grow Lights, Explained

After reading, you'll understand how PPF, PPFD, efficiency and coverage decide whether a grow light will actually grow your plants.

Updated September 25, 2026 · Companion to our Home & Kitchen review

Soltech Aspect Gen 2 LED Growlight - our top pick
In this guide

Grow lights are often sold on lumens, watts and bulb-equivalent claims, none of which tell you how well they grow plants. The useful numbers are photon output and the light reaching your plants. Hanging height and coverage matter just as much. Here is how to read the listing.

The 30-second version

  • PPFD is the key number, because it measures light at the plant.
  • Lumens are for people, not plants.
  • Efficiency is µmol per joule, so compare it across lights.
  • Height changes intensity, so hang lights to suit the plant.
  • Full-spectrum white works well, and looks natural indoors.

The products this guide is about

Our verdict on each, with the full reasoning on the companion review.

What actually matters

  • PPF - total plant-usable light from the fixture, in µmol/s. Higher means more light overall.
  • PPFD - light reaching a surface, in µmol/m²/s. It depends on distance.
  • Efficiency - µmol/J. It shows light per watt.
  • Coverage - the footprint a light serves. Panels list it by growth stage.
  • Spectrum - white, red and far red. Full spectrum suits most plants.
  • Dimming and timers - control intensity and hours. They make care easier.
  • Certifications - ETL or UL listings. They matter for long daily use.

The specs, in plain English

PPFPhotosynthetic photon flux, the total plant-usable light a fixture emits each second, in µmol/s.
PPFDPhotosynthetic photon flux density, the light landing on a spot, in µmol/m²/s. It falls as you raise the light.
µmol/JPhoton efficacy, how many micromoles of plant light per joule of electricity. Mars Hydro lists 2.0 for the TS 600.
LumensBrightness as seen by human eyes. It weights green light heavily and says little about plant growth.
Kelvin (K)The colour tone of white light. 3000K is warm, 5000K to 6500K is cool.
Full spectrumLight across the visible range, usually white, sometimes with added red and far red.
Far redLight around 730nm that influences flowering and stretching in some plants.
PhotoperiodThe number of light hours a day. Most houseplants do well with 12 to 16.

Green flags vs red flags

Green flags

  • Published PPF and PPFD.
  • An efficiency figure in µmol/J.
  • Coverage or PPFD at stated heights.
  • Dimming or a timer.
  • ETL or UL certification.

Red flags

  • Lumens as the only output figure.
  • "Equivalent to 600 W" claims.
  • Percentage energy-savings promises.
  • "High PPFD" with no number.
  • No certification information.

Who's who: the brands

  • Soltech - Known for design-focused pendant and bar grow lights for homes.
  • Mars Hydro - A grow light maker known for efficient panels for tents and indoor growing.
  • Barrina - A budget maker of linkable T5 and T8 LED strips and shop lights.
  • Sansi - A lighting brand known for ceramic LED bulbs and clip-on grow lights.

How to read a listing without getting fooled

Start with PPF and PPFD, and ignore lumens and wattage equivalents. Check efficiency in µmol/J, then the coverage or PPFD at your intended hanging height. Look at the spectrum, dimming and timer options, then certifications and warranty. Finally, match the style to where the plants live.

How much should you spend?

Budget grow lights include strips and clip-ons, often with little published data, fine for a few plants up close. Mid-range panels publish PPF, efficiency and coverage and suit seedlings and tents. Premium lights add design, dimming and published PPFD at real distances for living spaces.

Questions, answered

Can a regular LED bulb grow plants?

A bright white LED can help low-light plants, but it is not optimised for them and rarely lists plant figures. A dedicated grow light gives more usable light. For seedlings, use a proper grow light close to the plants.

Why are my seedlings leggy?

They are stretching for more light. Lower the light or increase intensity, and make sure it runs long enough each day. A timer helps.

Can grow lights burn plants?

Too much intensity too close can bleach or scorch leaves. Follow the maker's hanging height and use dimming. Raise the light if leaves pale.

Do I need a grow light in winter?

Many houseplants slow down in winter because days are short and light is weak. A grow light keeps them growing, especially in north-facing rooms. Herbs and seedlings benefit most.

Ready to choose? See our top pick, the alternatives, and the one we'd skip See the Grow Lights verdicts

Or jump to the head-to-head: Soltech Aspect Gen 2 LED Growlight vs Mars Hydro TS 600.

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