Chonk monster reading a folded plant-care map

CHONK DIRECTORY · Indoor plant care · Guide 7 of 9

Choose a grow light

Match the beam to the plant space, compare measured output, then install and time it safely.

2 min picture guideReviewed 29 August 202610 sources

Picture guide · three scenes

Light the canopy, not the label.

Check daylight first, match the beam to the plant space, then compare measured output and install safely.

01Match the footprint

Scene 1

Right beam, right space

Keep healthy window plants there; use a bulb for one plant, a bar for shelves or a panel for areas.[1][2][3]

  • Bulb: one plant
  • Bar: one shelf
  • Panel: wider area
02Read the map

Scene 2

Coverage beats big claims

Compare PPFD maps at the same distance and dimmer setting; check canopy edges, not only the bright centre.[2][4][6]

  • Ignore equivalent watts
  • Match test distance
  • Check canopy edges
03Set and watch

Scene 3

Timer on, water away

Begin at the maker's distance, use a timer, introduce stronger light gradually and let new leaves guide adjustments.[2][3][9][10][4]

  • Follow stated distance
  • Keep a dark period
  • Plugs stay dry
Open the full grow-light checklist

01

Start with the plant and the footprint

A healthy plant making well-shaped new leaves beside a bright window may already have enough light. Add a lamp for darker rooms, shelves, windowless positions or short winter days, then match its beam to the canopy: a bulb for one plant or compact group, a linear bar for a shelf and a panel for a dedicated area.[1][2][3]

  • Possible low-light signs include stretched growth, progressively smaller leaves, leaning, weaker flowering and loss of colour or variegation in some cultivars.
  • Pale, bleached or scorched leaves can signal too much light. Roots, watering, pests and nutrition can cause similar symptoms, so check the whole plant.
  • Light needs vary within broad groups such as ferns, Anthurium, Philodendron and Hoya. Use the exact species or cultivar and the growth you want as your guide.
  • “Full spectrum” describes the mix of wavelengths; it does not prove useful intensity or even coverage.

02

Read useful numbers, not equivalent watts

Ignore claims such as “400 W equivalent”. Actual watts describe electricity consumed; PPF describes total photosynthetic output; PPFD describes the useful light reaching the canopy; and DLI adds that light up across the day. Compare PPFD maps only at the same height, footprint and dimmer setting—a bright centre reading does not describe the edges.[2][4][6]

  • Look first for actual input power, then PPF and a PPFD map measured at a stated distance.
  • A wider plant or shelf needs even coverage, not only a high number directly below the centre of the lamp.
  • Distance changes intensity quickly. A 36 W bulb and a 100 W panel at the same height are not equivalent.
  • Dimming gives a panel useful headroom, but only if you record the height and setting when comparing results.

03

Set the timer, distance and safety

For general foliage plants, 12–14 hours of supplemental light is a sensible starting point; do not normally exceed 16 hours of total light a day. Begin at the maker’s stated distance, introduce stronger light gradually and watch the next leaves. Change one thing at a time so you know what worked.[2][3][9][10][4]

  • Use a timer and keep a consistent light-and-dark schedule; flowering plants may need a crop-specific photoperiod.
  • Buy the exact UK-market version. Check the rating plate, UK voltage and frequency, fused three-pin plug, mounting hardware and permitted link count.
  • Secure overhead lights mechanically. Keep plugs, drivers, timers and connectors dry and above watering level, and unplug before fitting, cleaning or adjusting.
  • For a heavy bulb such as the SANSI 36 W, use an open E27 fitting rated for its power, size and roughly 0.45 kg weight; do not use a tightly enclosed shade.
  • Second-hand: ask for the exact model and age, test every LED and dimmer, and inspect the plug, cable, driver, heat sink and mounting parts. Check whether any warranty transfers.

Explore the plants

Plant Index entries connected to this guide:

Bulb, bar or panel

Three grow-light setups to compare

Selected from current published specifications and UK availability for different jobs. Chonk has not laboratory-tested these lights. This is an unranked comparison, not an endorsement; verify the exact model, plug, voltage, output data, stock and warranty before buying.

Evidence used (10 sources)
  1. 1
  2. 2
    Important considerations for supplemental light ↗Iowa State University Extension and Outreach
  3. 3
    Lighting for indoor plants ↗University of Maryland Extension
  4. 4
  5. 5
  6. 6
  7. 7
  8. 8
  9. 9
  10. 10