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Why don't we have different vegetative / flowering lights?

Can Black Dog LED grow lights be used for both vegetative and flowering growth?


There has been a popular belief that plants need more blue light for vegetative growth and more red light for flowering. People discovered this a long time ago when the available artificial light options lacked adequate spectral coverage; people were forced to choose from either red-deficient blue-heavy light (metal halide [MH] or most fluorescent lights), or a blue-deficient red-heavy light (high pressure sodium [HPS]).

Given a choice between these limited options, the blue-heavy light clearly works better for vegetative growth, and the red-heavy light works better for flowering. But this doesn't mean that the plants don't want more red light during vegetative growth, or more blue light during flower. Indeed, many people have noticed that running vegetative and flowering lifecycles with a combination of MH and HPS ends up working better than just one or the other.

People note they get a higher-quality product in flower when they include more blue (MH) in flower, but because MH is inherently less efficient than HPS in terms of lumens or PAR per watt, using 1000 watts of metal halide and 1000 watts of high pressure sodium together doesn’t yield as much weight as 2- 1000W HPS bulbs. Because total weight is typically more important to growers, most don’t use a combination and the "blue for veg, red for flower" mantra lives on.

Black Dog LED used to buy into this mantra as well, and sold two different LED lights- a "veg" and a "flower" version, where the veg light had more blue and the flower light had more red. But when we produced a full-spectrum light with the right balance of red and blue, we found in side-by-side grows that it worked better for both vegetative growth and flowering.

The advantages to using a single, full-spectrum LED grow light for both vegetative and flowering lifecycles include:

  • Plants don't experience shock when changing spectrums. When plants grow leaves, they optimize the leaves for the light they are currently receiving. Whenever light intensity or spectrum changes, the existing leaves aren't optimized for the new conditions, and the plant undergoes shock. Leaves grown under the new lighting conditions will be optimized for it, but until new leaves grow the plant isn't able to best use the new light it's getting. By using the same spectrum for vegetative and flowering cycles, we eliminate this shock, and have noticed a decrease in flower time (1-7 days) and an increased yield when the plant was grown for its entire life under one spectrum.
  • Better quality plants while flowering. Plants grown under a red-heavy spectra for flowering tend to get leggy with weak stems. In nature, the upper canopies of plants block most of the blue light, but the far-red light penetrates to lower leaves and other plants. Plants that want full sun have evolved to encourage rapid stem growth when exposed to a low blue-to-red light ratio-- this makes them increase internodal spacing to grow tall and try to "stretch through" whatever is shading them out. This is why plants grown under HPS lights get taller, with weak stalks. By including the right ratio of blue light throughout flowering, internodal spacing is shorter, stems stay stronger, are less prone to breaking, and the plant expends less energy growing stems, and more energy producing flowers or fruits.
  • Better quality, denser flowers. Shorter internodal spacing means flower inflorescences (buds) are denser.
  • More flexibility. Since the same light can be used for vegetative and/or flowering cycles, you can deploy your lights to best suit your needs.

Using LEDs, we can fine-tune, down to the nanometer, the light we are providing the plant. Our Phyto-Genesis Spectrum® provides the correct ratios of blue to red, and far red light (and even UV light) to encourage the plant to stay compact while growing and flowering vigorously. The result is higher quality and quantity of plant growth at the same time, without sacrificing efficiency or falling into the old "blue for veg, red for flower" way of thinking.