Opinions on the best spectrum for growing

[Futuregrow]

Hello everyone!

The LED grow community worldwide have widely adopted warm white as an excellent flowering spectrum, with great results to show for it. We're seeing high yields with high quality, even where the light output has relatively low to no UV, and also relatively low 660nm frequency.

What we're also seeing is a push toward standardisation to some degree of the nomenclature around LED lights, in an attempt to do away with the bullshit we've all been force fed for the last seven years or so.

Right now it seems there is a big focus on the efficiency of grow lights, with primary players now quoting efficiency values in uMol/J... and rightly so, as it's easily calculable and quantifiable.

Something that isn't so quantifiable however, is the direct effect on plant growth that the spectrum has... it paints an incomplete picture.

Say for example you take two different hypothetical grow lights rated at the same wattage... the first one producing 2.0 uMol/J, the other 2.4 uMol/J. Upon initial inspection, one would assume the 2.4 uMol/J should grow more and better plants with a higher yield, right?

But much like judging the value of a car on mileage alone, this isn't really everything is it? After all, discrete 660nm red LEDs return very high uMol/J values in isolation.

We have some science such as the McCree study which has created a fairly universal curve, reporting on the photosynthetic efficiency of a wide variety of plants. And using this we can therefore convert PPFD from a known spectrum, into YPFD, a McCree weighted version of PPFD which is one supposed way to know the actual efficiency of a given light.

But how can we really quantify the true efficiency gain of spectrum quality, alongside the known electrical efficiency?

Going back to my hypothetical lights... what if the 2.0 uMol/J light had a much better spectrum for not only photosynthesis, but accessory pigment stimulation which has been shown to further improve and accelerate biological processes within the plant, leading to healthier plants with better terpene profiles and so forth?

What if the resultant synergy between spectral quality and efficiency actually led to the 2.0 uMol/J light being capable of producing higher yields and better quality than the 2.4 uMol/J light?

Personally I think taking warm white and adding discrete 660nm is somewhat rudimentary and almost lazy... and I haven't seen anybody produce any quantifiable evidence that there's a huge benefit in doing so. Only very recently for example, has it been determined that plants make much better use of green spectrum light when PPFD is high, and that it has better canopy penetration power than the reds and the blues.

Plants have been evolving under the sun for over 400 million years. Natural sunlight varies, and doesn't have this big red spike in the spectrum. I do wonder whether everybody is barking up the wrong tree thinking 660nm is all that. I have been configuring grow lights with a higher blue to red ratio since 2011; stretch sucks balls, more blue reduces it.

I'd love to hear your opinions on the best way to go forward:

Do you think we should be configuring grow lights to match the McCree curve? If so, then the McCree curve shows a lot more variety of blues in the mix.

Or should we be trying to mimic the sun more accurately, given that plants evolved under it?

Do you think efficiency in and of itself is sufficient to make a choice about grow lights?

Do you think we need a new unit or a new way of expressing the true efficiency of a grow light, not just the uMol/J by itself?

Knowing what I know and having studied this at university level, being able to control the biological processes that result from the light spectra seems to be massively overlooked by conventional spectrum grow lights... with almost too much of a focus on raw "horsepower" if you will. I believe having some control over plant morphology, phytochrome switching and all that good stuff should be the standard now... and we should really be considering spectral quality on top of efficiency.

Just remember, diodes are very cheap, and you can just use a whole bunch more at the same current if you want to up your efficiency... but designing an optimal, adjustable spectrum board... that's where it's at. I'm developing something like this at the moment.

[Hyakutak]

The thing is that there is probably no "best spectrum" and if there is one, it's probably not a static spectrum.

The "best spectrum" is probably depending on too many factors:

- Strain
- Environment (Temperature, humidity, growing medium, feeding, light schedule, light intensity)
- Grow stage (Days since seed/flowering)

In the case of MJ, The fact that we are selecting plants that grow better under HPS for decades make everything even more confusing/problematic...

One utopian solution would be to have a big database of grows with all the factors cited above perfectly monitored. We could create a "best spectrum" for each specific case.

My 2 cents...

[unkle_psycho]

There is a clear trend in the western approach to information, where we get so exited about new discoveries, that we loose sight of the big picture. We look for solutions, when all that exists are trade-offs. General discussions on what really matters (and how much) are very necessary.

You asked about efficiency, but really this is a point hyped by politicians and marketing folk. It is a balancing between light and heat. Very significant for those people growing in extremely hot environments (where outside grows are easy).
Cold areas that developed inside growing out of necessity, are often heating their space anyway, so really there is a question of quality of heat radiated from above vs what other heat source you have at hand. In a previous grow I switched 2 HID's for leds, and I had to add quite a bit of heating to compensate. I think the plants preferred the HID radiating heat on the top leaves, rather then the battery which was placed in the middle of the pots.

I have no belief in a perfect spectrum. In veg almost every plant has different node distances, and different size flower clusters. The right temperature in veg is the temperature that allows max stretch with solid colas. Too much stretch and you start having space between the nugs, which is inefficient. Do you think that a landrace sativa and stumpy indica would give best results with the same temperature? At least not inside, and at least not if comparing yield to area (cubic volume of useful area under the light, rather then yield per m2).

So claims of perfect spectrum are made by hustlers with a product to sell. Even the research side shows many plants reacting differently to different spectrum's. The heavy claims on universal spectrum's are made by industry, rather then researchers. Claims of superior 'propriety' spectrums should normally need quite strong proof to back them up.

I visited a friend recently, and he had just brought a new HID. Efficiency was actually not far from the most efficient commercial leds. The guys claiming absolute revolution to sell their stuff usually compare the best leds to the worst HID's.

Where leds offer the greatest benefit is in their ability to be taken close to the canopy. Halving the distance to the light quadruples the intensity (which is a greater benefit then efficiency), but all the led manufacturers I see are ignoring this potential, and trying to prove they can function like 1000w HIDs. They still benefit from multiple diodes and better penetration, but ignoring the potential to spread the diodes and get close to the canopy seems pretty damn stupid.

OH, one more thing. People talk about too much light intensity. I imagine its related to spectrum in some way. I put a bunch of seedlings under my 730w LG sulfur plasma light... distance to plants varied, starting at perhaps 10cm and not a single one was damaged in any way. HID's seem to damage them by heat.