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Grow light for seedlings

Updated: October 2026

A grow light for seedlings in the UK is most useful when chillies, tomatoes or herbs are sown before spring daylight becomes reliable. A warm propagator on a dull windowsill can produce fast germination followed by pale, stretched stems because heat does not replace light. Put an adjustable lamp above the tray as soon as shoots emerge, aim for a consistent day and retain a dark period. Our [plant lamps comparison](/hub/plant-accessories/plant-lamps) includes several 16-hour clips, while many cheaper models stop at 12 hours. The mount and timer therefore matter more than a dramatic wattage in the title. A qualifying purchase can earn us a commission at no extra cost to you.

A grow light for seedlings in the UK is most useful when chillies, tomatoes or herbs are sown before spring daylight becomes reliable.

Our top picks

Aumtrly Aumtrly 2-head clip

Best overall

Aumtrly Aumtrly 2-head clip
9.4/10about £18.99
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Garpsen Garpsen floor lamp, 80 LEDs

Rank 2

Garpsen Garpsen floor lamp, 80 LEDs
8.8/10about £32.99
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Ainiv Ainiv 48-LED stick

Best value

Ainiv Ainiv 48-LED stick
8.4/10about £8.99
View offer
On this page
  1. 1.Why a British windowsill stretches seedlings
  2. 2.Set the hours, then adjust the distance
  3. 3.Lamps in this set that suit a seed tray
  4. 4.If the seedlings are already leggy

Why a British windowsill stretches seedlings

Late winter and early spring bring short days, cloud and low sun angles. A window may look bright while supplying too little light for compact growth, especially when seedlings are warm. Chilli growers warn that bottom heat after germination can worsen stretching when light remains weak. Light germinated seedlings from above. Side light encourages leaning. A clip fixed to a shelf above a tray usually stays closer than a floor lamp several feet away. Do not leave the lamp on continuously. More hours cannot compensate for a weak head too far away. The grow light buying guide compares timers, mounts and electrical claims.

Set the hours, then adjust the distance

The Royal Horticultural Society gives about 16 hours for early tomatoes, and UK grower guidance commonly uses 14–16 hours for seedlings. That is a starting range. Daylight, output and temperature still change the result. Leaf & Cause suggests an LED roughly 5–10 cm above tomato tops. An RHS example puts T5 tubes around 60 cm above a group. Do not average those figures. If stems lengthen, move an adjustable LED closer in small steps if the leaves stay cool. If leaves bleach or feel warm, increase the gap. Timer faults are in how to use a grow light. A 12-hour button will not hide a 16-hour setting.
Aumtrly Aumtrly 2-head clip

Testsieger

Aumtrly Aumtrly 2-head clip
9.4/10about £18.99
View offer

Lamps in this set that suit a seed tray

The Aumtrly at about £18.99 is the clearest tray-shaped option: two heads, up to 16 hours, and 50 of 50 captured texts from the UK, including chilli and tomato seedlings. The clip is called fierce, one timer fault is reported, and 40 W is printed beside 5 V. The Wolezek at about £19.53 is another 16-hour clip, with three heads, 4.4 from 473 and 21 of 27 captured texts from the UK. Some reviewers call it dim, and one unit arrived with a broken earth prong. Garpsen also lists 16 hours, but a 67-inch floor lamp suits a plant stand better than a short sill. That choice is in the clip-on or floor comparison. Ainiv, Bamworld, SANSI, OHFAMO, vsshe, the dual-head Sonamindary and Uocub stop at 12 hours. Ainiv is the best value for one small plant, and it cannot run a 16-hour seedling plan. Fayleer and the single-head Sonamindary list 18 hours, with little or no UK review text in this capture.

If the seedlings are already leggy

Centre the lamp, reduce the gap if the leaves stay comfortable, and keep a consistent day. Take off ongoing bottom heat after germination unless the crop still needs it. Warm compost and weak light make stretching worse. When potting on tomatoes, you can plant them more deeply because buried stems can form roots. Do not transfer that to every herb or chilli. Elongated tissue will not shorten. Stronger new growth is the aim. A collapsed or rotting seedling is not fixed by more light. These lamps are not waterproof, so keep adapters off wet compost.

Common questions

Do UK seedlings need a lamp before April?
Not every seedling does, but early indoor sowings often benefit because UK days can be short and dull. Chillies and tomatoes started in late winter are common examples. Use the brightest available daylight first, then add a lamp if stems lean or stretch rather than treating the calendar date alone as proof.
How many hours should a seedling lamp run?
UK guidance commonly uses about 14–16 hours for early seedlings in weak natural light, with a daily dark period. Start within that range and account for daylight already reaching the tray. A lamp that stops at 12 hours may still supplement a bright sill but cannot reproduce a 16-hour setting by itself.
How close should the grow light be?
There is no universal distance. One UK tomato guide suggests 5–10 cm for its LED advice, while an RHS example uses about 60 cm for T5 tubes. Follow the instructions for your lamp, keep it above the tray and adjust gradually if seedlings stretch or leaves show heat, bleaching or dryness.
Which lamps here can run for 16 hours?
Aumtrly, Wolezek and Garpsen list a 16-hour timer option. Aumtrly and Wolezek are clips that fit naturally over trays. Garpsen is a floor lamp. Ainiv, Bamworld, SANSI, OHFAMO, vsshe, Uocub and the dual-head Sonamindary stop at 12 hours.
What should I do with already leggy tomato seedlings?
Improve the overhead light and consistent daily schedule first. When potting on tomatoes, you can bury part of the stretched stem because tomatoes can root from buried stem tissue. Do not assume the same method suits every species, and remember that old stretched growth will not become shorter.
Does a heat mat replace a grow light?
No. A heat mat warms compost and can speed germination, but it supplies no light. After shoots emerge, continued warmth with weak light can make stretching worse. Manage temperature and illumination separately, and follow crop-specific germination guidance rather than leaving every tray on heat indefinitely. Sowing timing is in seedling heat mats before the last frost.

Related pages

Plant lamps

Best plant lamp: Garpsen floor lamp or Ainiv stick

Grow light buying guide UK: check mount before watts

Clip-on grow light vs floor lamp: which shape fits?

How to use a grow light: hours, distance and safety

Sources

Public UK sources used for hours, photoperiod, plugs, and lighting labels, plus the amazon.co.uk listing facts in this comparison. Shelf prices and star lines are those UK figures. No listing in the set prints a PPFD.

  1. RHS: Artificial lighting for houseplants (retrieved 16 October 2026)
  2. RHS: How plants sense the environment (retrieved 16 October 2026)
  3. RHS: How plants use light to grow (retrieved 16 October 2026)
  4. GOV.UK: Electrical Equipment (Safety) Regulations 2016 (retrieved 16 October 2026)
  5. legislation.gov.uk: Electrical Equipment (Safety) Regulations 2016, regulation 35 (retrieved 16 October 2026)
  6. GOV.UK OPSS: Fecida LED grow light UFO600, report 2305-0074 (retrieved 16 October 2026)
  7. legislation.gov.uk: Ecodesign for Energy-Related Products and Energy Information (Lighting Products) Regulations 2021 (retrieved 16 October 2026)
  8. Mike’s Garden: Which grow light to buy (retrieved 16 October 2026)