Collection: Lighting for Greenhouse

Two Kinds of Greenhouse Lights

Greenhouse lights fall into two groups that are often confused, and buying the wrong one is a common and expensive mistake.

Grow lights supply the wavelengths plants use for photosynthesis, at an intensity high enough to matter. Ambient lights let you see what you are doing and make the space pleasant to sit in during the evening. A festoon string will not grow anything, and a grow light is unpleasant to sit under.

When Grow Lights Earn Their Place

Between November and February a British greenhouse receives few enough hours of usable light that growth effectively stops. Supplementary lighting extends the day and keeps propagation moving through the period when it would otherwise stall.

• Seed raising in January and February, where daylight alone gives leggy, weak seedlings.
• Overwintering plants that need to keep growing rather than go dormant.
• Any part of the house shaded by a wall, hedge or the frame itself.

Distance from the plant matters as much as output. Light intensity falls away sharply with distance, so a fitting mounted at the ridge delivers far less at bench level than the specification suggests.

Mounting

Overhead fittings suit general coverage across beds or benches. Side mounted bars work for vertical growing and wall shelving. Clip on and hanging fittings suit a propagation area where you want light concentrated in one spot.

Whichever you choose, it has to be adjustable. Plants grow towards the light and then get too close to it, so a fitting that cannot be raised will scorch what it was installed to help.

Damp and Electrical Safety

A greenhouse is a wet environment with a hard floor and a lot of glass. Fittings must be rated for outdoor or damp use, and any supply should be installed by a qualified electrician and protected by an RCD.

Indoor fittings and domestic extension leads are not suitable, whatever the temptation. Condensation runs down the inside of the glazing every night and finds any fitting that is not sealed.

Off Grid Options

Solar lighting suits allotments and any greenhouse without a supply. It works well for ambient light and for modest supplementary lighting, though it will not match a mains grow light for intensity.

If you are running power to the house anyway, consider what else will use it. An electric heater and a circulation fan are the usual companions, and planning the circuit for all three at once is cheaper than adding to it later.