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Grow lights

Morning, sorry if this is a silly question. I now have an LED grow light in the greenhouse over my seedlings. How long should I leave it on for during the day/night? Does it need to be a minimum distance above the top of the seedlings to help with air circulation and stop too much heat hitting them.
Many thanks


  • Pete.8Pete.8 Posts: 10,254
    You shouldn't really need additional light now we're past the Spring equinox.
    But typically 18 hours on and 6 off is the way to go.
    LED lights can be just a few inches above the plant tops, but depends on the wattage. Hold your hand just below the light where the plant tops will be, so long as it's just warm that's ok.
    Knowledge is knowing that a tomato is a fruit.
    Wisdom is not putting it in a fruit salad.
  • KiliKili Posts: 1,042
    edited April 2020
    You don't need lights on during the day if your plants are in the greenhouse.  I aim for 17 hours a day of light so adjust your lighting to suit that or more if you think you need it. My seedlings are in the house under grow lights on a timer. However its not just light, you need a combination of light and heat if your trying to bring seedlings on with faster growth. Its still a bit cold for rapid growth outside, unless your using a heat source of some sort to raise temperatures although, temperatures are set to rise as we approach May ( I hope)

    The distance above your seedlings depends on what type of grow light it is. The T5 grow lights give off very little heat so can be positioned much closer to the plants, LED lights I have no idea as I have never used them. What type of light is it?

    'The power of accurate observation .... is commonly called cynicism by those that have not got it.

    George Bernard Shaw'

  • Hi, I've bought them this year as I always seem to end up with really leggy, weedy looking seedlings. I bought a couple from Ikea, they're not giving off a lot heat so are a few inches about the tops. The blurb on the website says the PPFD is 100 umol/m2/s - whether that's a good thing or not I've no idea. I think next year I'll invest in something a little more substantial and not plant too early - thanks for your advice. Will put them on the timer for a few hours evening/night time
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