Grow Lights – Do they work?

As I start carefully wrapping up my grow lights and put them away for another year in the loft – where they’re safe – I thought I’d answer a few of the questions I often get about grow lights.

Propagators with Lights

Propagators with Lights – Vitopod with 3 tiers, Vitopod with 2 tiers and Geopod (without lights) on the right.

I get quite a few emails about grow lights, some asking very basic questions and some very technical questions where I think the questioner probably knows more about grow lights than I do – or want to know, for that matter.

The very technical questions tend to be about what wavelengths of light are best to initiate flower formation and suchlike. The answer is that I don’t know and they need to do their own research. I think I know what they’re growing.. and it’s not a vegetable or a fruit and I’ve no experience growing it!

What Grow Lights to Buy?

Most often I’m asked what sort of lights to go for. There are quite a range of lights available – fluorescent, LED and mercury tungsten etc. At first glance the choice would seem obvious – LED although fluorescent lighting is still popular. LED (Light Emitting Diodes) offer flexibility in the spectrum of light they can offer so could be ‘tuned’ to suit the plant’s optimum for different stages of growth.

LEDs are cheaper to run as they give out more light per watt of electricity than fluorescents because less energy input ends up as heat. However, because of the way I use grow lights the heat given off by fluorescents is usually a benefit and the cost of running the lights is offset by a reduction in heating costs.

Lifespan of Growlights

In theory LED lights could last about 10 times as long as fluorescent lights but in practice it depends on the electronics that power the actual diodes. I’ve had too many cheap LED house light bulbs that haven’t lasted as long as an old fashioned incandescent bulb. Fluorescent tubes are a very proven technology.

Reviews of LED grow lights aren’t a lot of help when it comes to lifespan – a 50,000 hour lifespan would take over 5 years to test. Fluorescents are an older and simpler technology, well proven with known lifespans.

Early in the season I use the grow lights for 12 hours a day to extend the daytime and supplement the low light levels of late winter and early spring. By late spring when the actual daylength is 12 hours or greater, I just have them on for 3 hours from dawn and 3 hours before sunset. This adds extra energy to the plants when the natural light is weakest.

So my lights are on for roughly 1,200 hours a year and should last about 8 years, perhaps 10 years with luck.

Sunblaster Grow Lights

My favourite lights are the Sunblaster fittings. They comprise a fitting which can be interlinked with another fitting and a reflector that is claimed to reflect 99% of ‘wasted’ light back into the plants. The tube is a T5 (5/8 inch diameter) fluorescent grow light with a 10,000 hour life.

Do Grow Lights Work?

Tomatoes under Grow Lights

Tomatoes under Grow Lights – The plants directly under the lights are 2 to 3 ins. higher.

One simple question I loved was “Do grow lights work?”. The answer is a resounding Yes! You can grow purely under artificial lights which proves they work but even as supplementary lighting which is how I use them, you can tell the difference in the plants. The tomatoes and peppers are sturdier and more advanced than most of the ones in the garden centres.

With my Vitopod propagators there are 2 Sunblaster grow lights which is adequate but the plants directly under the lights are actually about 3 ins. taller than the plants to the edges – even those who are getting more natural light.

Because you can add extra side layers to the Vitopod it is easy to keep the lights just above the top of the plants as they grow. This maximises the light energy the plants get without burning the growing tip. The Geopod is fixed height – so good for getting things going but not so useful once the plants are getting larger.


Overall, I feel that grow lights are a good investment for the serious gardener wanting to bring things on ahead of the season. They’re not expensive to buy given a good lifespan and they’re not expensive to run – particularly when you’re paying for heating anyway.

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Posted in Allotment Garden Diary
12 comments on “Grow Lights – Do they work?
  1. g evans says:

    I wonder if solar string lights would work, as they come on automatically at dusk, and stay on till dawn.

  2. euan campbell says:

    Good stuff, I was trying to figure out whether I should invest in some Led grow lights and you have convinced me to go for it!
    much thanks

  3. Simon says:

    I only have north facing Windows in my flat, so I will have them in again as soon as a few green tips show. Onions, Chilis and Red peppers should come through next week. You might get a visit from the drug Squad, people use them for that sort of plant as well.

  4. Shiv says:

    Hi, your article is informative. Do you know whether using grow lights in an outbuilding with no heating works for germinating plants? I can cover the makeshift enclosure in a polythene sheet if that helps. Being in southern England, I am looking to germinate my vegetable plants around end of winter under grow lights in order to transplant a healthy grown plant to my veg patch a bit earlier. Thanks.

    • John Harrison says:

      Hi Shiv
      Growlights won’t help germinate seeds. They need the right temperature to break out. See Best Temperatures for Seed Germination Once they are germinated, lighting will help ensure strong growth. If you can power lights, then you must have electricity so can set up a propagator to provide heat. You could start them in half trays or pots then prick out and move into larger pots or modules in cooler conditions. I like fluorescent lights rather than LED because of the warmth from them.

  5. Rachel Firth says:

    I am wondering where you got your fittings for the sunblaster lights. I just bought some and I assumed they would just sit on top of my propagator lid (the photos on selling sites suggest that), but no…

    • John Harrison says:

      Greenhouse Sensations sell the perspex supports that hold the lights on my Vitopods. They’re pricey but you only buy them once and use year after year.

      • Rachel Firth says:

        Hello I bought some of those Greenhouse Sensation light supports, as I see you have in the photo. I am really struggling to get them to stick. (I have tried cleaning the surfaces, used a little moisture etc.) Do you have any tips? I am considering resorting to superglue…

        • John Harrison says:

          Make sure both the suckers an sides of the pod are clean (damp cloth with drop of detergent) then press on the sucker, balancing the pressure on the other side of the perspex – so you’re squeezing two hands together.
          They work pretty well for me.

  6. Ruffy Ruffles says:

    I don’t know the science but, yes, they do work and plants are earlier, bigger and stronger.
    Tip – use two Vitopods. One unlit for germination at recommended temperatures, the second with Sunblaster lights for growing on and kept at a lower temperature.

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