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How High to Position Growlights

Growlights will certainly help you grow very early crops but where should they be placed for maximum benefit?

Propagators with Grow Lights

Vitopod propagators with Sunblaster T5 grow lights in my solar shed

A reader emailed:

I have a heated bench. This uses a yellow cable which heats sand and it is successful. Last year I purchased two of growlights to prevent leggy seedlings. What is the best way to set these up on the heated bench, how high above the compost etc.? The brand is Sunblaster 39 Watts.

Where to position growlights is a bit of an art. The nearer the lights are to the leaves, the more energy will be transmitted to them powering the plant’s growth. However, as the lights get nearer to the plants, it spreads less. So we want the lights high enough to spread light evenly over plants.

The other thing to consider is heat. The Sunblaster T5 lights are fluorescent and do give off heat as well as light. They convert much of the energy input to light and are roughly five times more efficient than an old-fashioned incandescent light bulb. Even so, they still give out a considerable amount of heat. Much of this heat will rise away from the plants but a fair amount will go down and heat them.

LED Grow Lights

Incidentally, there is a lot to be said for the newer LED growlights. They are more efficient and in theory should last longer than fluorescent lights. The problem in the past has been the cheap electronics that make the LEDs work. They’ve tended to burn out well before they should. Happily, the technology is becoming mature now and reliability is improving.

The light can be tuned to the ideal spectrum for the type of growth required although I don’t think that is particularly useful for a home grower.

Being more efficient, LED lighting systems generate less heat but that is less of a benefit than you might think at first for home growers. We tend to need heat at the time of year we need additional light, so that ‘waste heat’ is actually useful.

Vitopod Propagators with Lights

I use a Vitopod propagator which is thermostatically controlled and has a 100 watt heating element. I actually measured the electric consumption with and without growlights and found much of the extra electricity used by the lights was compensated by reduced electricity consumption by the propagator.

Generally I use growlights for two purposes; firstly to extend the very short days of mid-winter, convincing the plant it’s time to grow out of season. Secondly, providing additional energy to the plants. There’s little strength in the light on a grey, overcast winter’s day.

The Vitopod lighting kit comes with brackets that hold the lights about 10 ins., 25 cm above the level of the compost in a seed tray. This seems ideal to start with. Once the plants grow above 6 ins., 15 cm, I put another layer onto the side of the Vitopod. This automatically raises the level of the lights.

Posted in Allotment Garden Diary
2 comments on “How High to Position Growlights
  1. Morene Griggs says:

    Having had (and loved) a big and a small vitapod for many years, following your article last month I bought the growlights for my small one. I have not been able to get the suction valves of the support kit to grip securely and then found there was no way to lift the lid off the vitapod for watering and maintenance of the plants without removing the lights completely. I have ‘Heath Robinson’d’ some wedges to ease the support brackets apart sufficiently to slide the lid off but it is not ideal. How do you manage, am I missing a trick somewhere? Greenhouse Sensation had no suggestions other than ‘Remove the Lights.’

    • John Harrison says:

      Hi Morene – With the supports ensure the sides and suckers are clean. Press firmly, I balance the pressure with one hand inside the sides and the other pressing the sucker. I’ve not had a problem getting them to stick.
      As for watering etc., I tend to put the light at the front on top of the rear one which allows me enough access to water etc. (after slipping the lid off) and then replace the light after. Even taking them both off the top and replacing takes but a few seconds.
      Good luck – I wouldn’t be without mine.

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