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Ask Erik:RAW! - Full Spectrum Grow Lighting: Maximum Flux or Wasted Photons?


I have been growing for a while and have started to research ways to improve my garden. I know there are lots of different light sources to choose from, but what I want to know more about is spectrum. It seems that even if I want to stick with HID or whether I switch to LED or even Plasma, I have some choices to make regarding spectrum. I love the way my plants look and grow in veg under my high output fluorescent lighting which is full spectrum. What about full spectrum lighting for the bloom phase? Everyone says you’ve got to use HPS (orange light) or don’t expect much. What do you think?


Full Spectrum Building Steam

This is a big question. I am predicting a trend towards full spectrum lighting for the indoor growing scene coming up in the next while. There are some benefits to full spectrum lighting, although to some extent any increases in yield may be strain (varietal) dependent in the age old MH (metal halide) versus HPS (high pressure sodium) debate. To add more fuel to the fire, there is other intense full spectrum lighting available to growers besides Metal Halide these days including:

  • Induction lighting
  • Plasma Lighting
  • Full Spectrum LED
  • VHO Fluorescents

It’s Not Where You’re From, It’s Where You’re At

Over the last five years there has been a strong shift to growing strains that come from different growing regions than many of the strains that were popular when growing literature really started to come together. So in a sense, some of the old books don’t always apply 100% to today’s grow rooms, strains and the lighting technologies available.

In the past, growers almost always found they got bigger yields from the bloom phase when using more orange-red lighting sources like HPS, while more blue to full spectrum rich lighting sources like MH were reserved for keeping plants shorter and bushier in the vegetative growth phase. Today, savvy growers with the marbles to experiment are finding that some of their newly popularized strains are responding more favorably to full spectrum light sources in more ways than one.

PAR for the Course

A detailed answer as to exactly why full spectrum lighting sources create better results in some strains versus traditional orange-red sources is beyond the scope of this column.

In short, the full spectrum grow light source likely mirrors more closely the quality of the sunlight where the genetics originated, for example, in more northern latitudes rather than more southern or equatorial growing regions.

It could also be that natural plant growth is more seasonal in these northern varieties versus genetics originating from closer to the equator. The quality of light shifts with season in many parts of the world and not just day length as you get further from the equator.

Tailored lighting sources such as the intense pink to purple hue produced by high output and effective LED bloom grow lights can still be very effective, but consider how little we as growers and scientists really know about “lighting nutrition.” It’s like thinking that all plants would like the same balance of fertilizer elements. We know this isn’t true, so why is it that a lot of us think that one photosynthetic response curve applies to all plants and strains at all phases of growth? It’s because the ability to tailor plant growth spectrums from intense artificial light sources has been relatively limited until more recent times.

Full Tilt

Growers now have the ability to tailor very exacting spectrums, opening up an exciting time for discovery when using different qualities of full spectrum lighting. And yes, your standard MH lamp can produce some great results in the bloom phase with many of today’s popular indoor varieties, so it might be worthwhile for you to experiment. Also don’t forget that when it comes to flowers and fruits just because it looks bigger doesn’t mean it’s going to taste better or weigh more. This is an important consideration because MH is known to create denser, more compact flowers, buds and fruits in the bloom phase, although potentially every bit as heavy or greater versus HPS.

Cheers, Erik Biksa

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Metallica and indoor growers have more than a few things in common, including understanding the importance of hitting the lights.
Last modified on Monday, 08 October 2012 19:05

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