Light. Specifying and measuring it: NOT so easy. I call shenanigans

[Theo]

So you want to buy lighting and you are looking at the specs, tests, experiences from your peers, and of course you want the latest and greatest.

In this first post (because it is going to be a series) I want to focus on specifications.

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How should a light/lamp/fixture be specified?

Basically there are only four specs that really matter:

1. PPF
2. Spectrum
3. Power use
4. Light maintenance.

In this post I am just going to touch the basics.

PPF
PPF, Photosynthetic Photon Flux, is a measurement of the amount of light that is generated by the source. It has got nothing to do with the intensity incident on a surface, nor can you measure it by just measuring the intensity on a surface.

The reason why you need to know PPF is to get a grip on the efficiency of the lamp/fixture. A higher PPF per W of used energy means a more efficient lamp/fixture.

Why is it no use measuring the intensity incident on a surface: That intensity depends on the concentration of the light by the optics (reflector or lens) and the distance to the source. Think about a focusing flashlight: you can, with the same light, create one focused beam of intense light on a small surface, or a lower intensity light on a much larger surface. If you would use 10 flashlights to light one square meter, then the average intensity would be the same id you would have 10 concentrated separate beams or 10 wide, overlapping beams. The latter would be a much better solution though, because the uniformity would be much better.

Which brings me to misleading specs. This is how many manufacturers do that:

• They show the intensity straight under the lamp
  They call it PPF, but it isn’t. It’s PPFD at a distance. That is never an indication of the total output of the light, as I explained here. Just reduce the beam angle and you get spectacular results. Yes, on a tiny spot. The total amount of light is what matters, because that is what you are going to bring to your crop! Divide PPF by lit surface in square meters and you get the intensity: 2000 umol s-1 (PFF of the source) spread over 2 square meters gives you 1000 umol m-2 s-1 (PPFD - intensity incident on the surface). This is also why 4x4 grid measurements are so awful: first of all you do not integrate all the light (a lot of light will be outside the measuring grid and not taken into account), and secondly because of the measuring points there is a focus on the spot straight under the lamp. ANY deeper reflector will give you a better result. Crap.

• Crazy energy savings
  “My 500W fixture does 2000 umol! It can replace a 1000W HPS” No it can’t and even scientifically it can easily be debunked based on that sentence. If you would be able to convert ALL energy into photons you would get 4-4.5 umol per Watt, and no heat generated. That is Star Trek technology. The most efficient LEDs in labs do about 3 umol per Watt and they would never be used in a fixture: Way too expensive and nor practical. HPS does 1.9 umol per Watt (max fixture output). So you can not be 50% more efficient, and even 30% more efficient would be a challenge! The best reliable PPF/W specifications from respected LED manufacturers I have here for you (though some UNPUBLISHED them):
  
  You see that the cost per umol is 3.3x up to an astonishing 17.7 times as expensive as HPS! Some manufacturers go completely crazy on their efficiency. I took the lowest average price I could find for the LED fixtures, some are 40+ or 100+ prices, and the advertized price for the Gavita at Growershouse.
  Take a look at this video. See if you can detect the bullshit. https://youtu.be/iNBJpTCIERY - make sure to visit their website to see if you find ANY PPF specifications (you won’t!). Their previous fixture, that used 460W, would be able to replace a 1000W HPS. Now their NEW fixture, which is much more efficient and outputs way more light at a higher power… you guessed it… replaces a 1000W HPS fixture (or probably 3 according to the video I shared with you)

Spectrum
This is a subject for a completely different discussion. suffice to say that most HPS lamps have a very similar spectrum, but god is in the details… high red/ far red ratios for example can have a great influence on your crop. But, and HPS lamp is NOT a narrow spectrum lamp. In fact, it has a way wider spectrum than any red/blue LED fixture! The only thing it lacks is primarily blue light: current HPS lights only emit about 3-4% blue light. 6-10 would be great. Talking about that: “My HPS lamp delivers 25% more blue light!”. Sounds great, right? That 25% is 1% or less extra blue light. Get over it.
At a horticultural lighting conference the researcher that led the discussion asked the attending lighting manufacturers to stand up if they could provide him a spectrum that yielded 10% more than the standard HPS spectrum. Nobody in the room stood up.

Power use
If you see, in a brochure, the total wattage of a fixture to be the same as VxA then you know that is probably invented by a clueless marketeer who never finished his high school physics class. There is always a power factor involved, and drivers for voltage ranges between 120 and 240V are usually no more efficient that 95%, which brings me to measurement of fixture efficiency: A 1000W HPS ballast should give 1000W to the lamp, and uses about 50-60W internally in the process of converting voltage and internal heat dissipation. Any ballast using under 1050W in a real life situation will underpower the lamp. There are small variances in the lamp output end electronics, up to 4%, so there is a variation, even when comparing fixtures. just by lamp output and electronic variances this already can easily be 5%.

A trick by many manufacturers is to actually overdrive the lamp a bit, let’s say 5-10%. So at 100% output you already get 5-10% more light. That doesn’t mean that the fixture is more efficient, it uses more power to do so. Without a measurement between the ballast and the lamp to measure what actually goes to the lamp, you can not detect that. We use a 30k power analyzer to measure that.

In any case: it is no use replacing a HPS fixture with an LED fixture that produces less umol per W.

Light maintenance
Why do people change their lamps? It is because, over time, lamps output less light. They become less efficient. MH is the champion: it can lose easily 20% of light over 3-4 months of use. A good, horticultural HPS light only loses 3-4% over a year. The year after that these losses could go up to 8%, which is why you change your lamp every year to get the optimal output.

Now when a distributor buys a light from manufacturer X in C, he usually asks for the output specs and they look great on paper: 2100 umol! Not so. While you are unable to measure the actual output yourself (having a calibrated Ulbricht sphere), 98% chance that this is not correct. Tests show that.

But what most people do not know is that many lamps do NOT have that good of a light maintenance. Some manufacturers, such as Eye Hortilux, give you recommendations when to change your lamp (8 months), which is usually at 5% or more light loss. Most however do NOT publish their light maintenance over time. Any reliable lamp manufacturer will.

For LEDs it is different. We work with an L90 (which means the time it takes to lose 10% of light). Let’s say this is in 25,000 hours - or 5 years of intense use. You will need to use them this long as they are way more expensive than HPS. After a few years you will see that the light output is lower already. Over the complete lifespan of the light it will be average 2.5% lower. (Good!!!) HPS loses about 3% per year and after that you just change the lamp. So average 1.5% lower (in reality a bit less than that as many lamps deteriorate not in a linear way).

So, there is just a little ramble about some things you should be aware of when looking at specifications.

Remember:

1. There is no magic spectrum that performs 30, or even 10% better as in photosynthesis and yield
2. There is no magic lamp that performs 50, or even 30% more efficient than HPS
3. There is a BIG difference between PPF and PPFD. Do NOT fall for the “PPF at a distance” trap, it is unscientific and does not represent fixture efficiency nor output,

Beware of snake oil!

[Theo]

For more information about PPF and PPFD, visit our YouTube channel. Here are a few relevant videos:

https://youtu.be/JXChaYYmzHg - about PPF and PPFD
https://youtu.be/9g3FTpKZ_pA - how to measure lamp and reflector output and efficiency

[nicholas]

Great topic @theo! Thanks for posting it.

[Theo]

One thing I need to add maybe:

50% more efficient is not the same as 50% energy savings, that would be 100% more efficient.

So be very aware of how these specs are worded. Neither of them by the way are true.

[CaliforniaLightworks]

Thanks Theo for this excellent overview!

This is a good defense of HPS technology and includes most of the standard arguments given by HPS manufacturers and you make some great observations on how lighting manufacturers provide misleading information. We agree that this is a problem.

However, there are so many inaccurate assumptions and conclusions in your post that I could not help but respond. I am responding as a representative of California Lightworks, an LED grow light manufacturer based in Southern California.

Your approach represents a typical discussion among commercial lighting manufacturers – it’s all about physics and economics. Period.

However, in the real world, growers do not care as much about physics or theoretical light output as they care about plant biology – how plants use light for yield, quality, chemical profiles, what they can sell their product for, long term operating costs and the environmental impact of their grow strategies.

On these key points HPS falls short and represents a technology in decline that is being quickly replaced by LED in almost all other lighting applications. This will be even more true in horticultural lighting. We are at the tipping point.

While this discussion can go much deeper and you fail to mention many key points, I will only respond briefly point by point to your post:

How should a light/lamp/fixture be specified?

PPF – NOT THE BEST WAY TO EVALUATE PLANT LIGHTING

While I agree with your point about surface intensity versus total output of a fixture, there are several problems with this approach.

First, PPF is only accurate when you are comparing two fixtures with identical spectrums. Once the spectrum varies between two fixtures you are no longer comparing apples to apples. Comparing HPS to
LED fixtures with widely varied spectrum is misleading if not irrelevant.

PPF ignores how plants use light. PPF accounts for the total number of photons generated by a fixture in the 400-700nm range in a closed sphere. However, ALL PHOTONS ARE NOT CREATED EQUAL. Peak photosynthesis occurs from 440nm to 475nm and from 620nm and 660nm. The photosynthetic efficiency outside of these ranges is extremely low - which is where much of the light from an HPS fixture is focused - not to mention the huge amount in wastful infra red heat.

If PPF were the only criteria, LED manufacturers could just use the highest output PPF spectrum and just forget about how plants use light. We’ve seen some LEDs in the green spectrum that can register off the chart PPF ratings but these will be horrible lights for plants.

Designing a grow light to maximize PPF ratings is not the goal. The goal is to provide the best possible spectrum at the best possible efficiency for the specific plants species and grower objectives.

HPS is a fixed spectrum and can only change slightly by changes in pressure. As the pressure increases, the spectrum shifts to the red, as bulbs get old the pressure decreases and the spectrum shifts more to yellow/green. Time to change the bulb again! PPF ratings between two HPS bulbs or fixtures is meaningful. PPF comparisons between two LED fixtures with identical spectrums is also relevant. PPF comparisons between HPS and LED is highly misleading if not irrelevant – in the same way PPF comparisons between two LED fixtures with different spectrums is misleading. Plants do not care about how many photons they are exposed to – they care about how many photons they can use. Much of the HPS photons that are counted in the PPF ratings are reflected by the plant and are of little use in photosynthesis.

Evaluation of horticulture lighting it must be based on the light output that is most relevant to the plant being grown and the specific objectives of the grower.

PPF measurements ignore this central fact.

We need other measurement criteria to compare two fixtures and even more so to compare two different lighting technologies.

CRAZY ENERGY SAVINGS – YES, WE CAN

Once again, you are assuming that all photons are equally efficient in photosynthesis. They are not. Plants use very specific light spectrums for photosynthesis and this is very well understood – even by HPS salesmen.

If you eliminate all the energy related to generating light spectrums that the plant does not use you can easily get the same grow results with significantly less energy. The savings with LED are more about better spectrum spectrum rather than light efficiency – even though LEDs are much more efficient in this measure as well.

This is the main savings offered by LED versus HPS – tailored spectrum for plants - and understanding this is critical in making light design and purchasing decisions.

While some LED manufacturers may exaggerate results – especially when it comes to yield - you can get crazy energy savings with LEDs over HPS. It happens every day! Just use a more efficient way to generate light and eliminate or reduce the useless spectrums. This is not rocket science.

LIGHTING EFFICIENCY TRENDS – SORRY, HPS IS DOOMED

Even if we ignore the spectrum argument, LEDs are already much more efficient from a pure efficiency point of view than any bulb based lighting technology. You say yourself that HPS efficiency has peaked at about 1.9 and LEDs have already passed 3.0 in the lab. You say that these higher efficiencies are will never be put into a fixture as they are too expensive. I have news for you – yes, they will. As with all things electronic, as the manufacturing quantities go up, the costs come down.

In our LED production, we use primarily Osram LEDs. We order in large batches about every six months. When each new batch arrives we quickly assemble a test fixture and measure the light output compared to the last bath. On average the output has gone up about 5% every six months – with no increase in cost! The last batch was up 15%. This trend is not slowing down – it is speeding up.

What we see in the lab today will be on the market in 18 months. It will be interesting to see how the HPS world responds. There is little or no R&D investment in HID technology in most all other lighting applications. These have gone overwhelmingly to LED.

So here is the real question – How long will the horticulture industry cling to HID?

COST PER UMOL – ACTUAL ROI IS KEY – NOT INITIAL FIXTURE COST AND PPF

You present an interesting chart showing cost per uMole with various fixtures. You show that this cost is so much lower with HPS that it is hard to imagine how anyone would consider LED. However, this is not really a fair analysis of what the real costs are.

Frist, much of the light put out by HPS is not used by the plant very efficiently. It is possible to eliminate about 40% of the light from HPS without affecting plant growth and yield. PPF is not the real measure of light output for plants.

Second, you are using a snap shot cost evaluation – the light output per dollar based on the initial purchase price. No grower looks at it this way. It is a combination of yield, plant quality, energy usage and bulb replacement cost over time – including the cost of the bulb and the cost to change it as well as environmental concerns.

In the old days when growers were under-financed and nervous about getting shut down they only cared about their next harvest. Obviously, a cheap HID fixture was an attractive proposition. However, as cannabis production moves into the light of day it is all about return on investment – not immediate light output per dollar.

You say yourself that any grower considering LED needs to think at least on a five-year basis. Obviously, this paints a different picture. When considering all the costs; initial fixture cost, bulbs, the cost to change bulbs, energy usage, cooling issues, etc. HPS loses its cost advantage entirely.

Here is a simple example:

• Assuming equal yield and quality per fixture (A big assumption, I admit)

•   1000 watt HPS DE and a top level 600 watt LED optimized for bloom.
  

•   Over a five or ten year period for 100 lights
  

• Flowering continuously for 12 hours per day

•   Fixture Costs – assuming the costs per your example
  

•   Bulbs – Using once a year replacement and a cost of $ 75.00
  

•   Bulb replacement cost – assuming $ 20.00 per bulb
  

•   Energy Savings – assuming 40% savings with LEDs at an electricity cost of $ .15 per kilowatt hour
  

HPS @ 5 years

Fixture cost 100 @ $ 450.00 = $ 45,000
Bulbs 500 @ $ 75.00 = $ 37,500
Labor to change bulbs 500 @ $ 20.00 = $ 10,000
Power – 21,900 hours @ $ .15 = $ 65,700
Total cost with HPS = $ 158,200

LED @ 5 years

Fixture cost 100 @ $ 899.00 – $ 89,900
Power - $ 65,700 @ .40 = $ 39,420

Total cost with LED = $ 129,320

A net savings of $ 28,880 with LEDs over HPS over five years – over 18%. A pretty solid return on investment.

Obviously, these savings will only increase every year. Most quality LEDs are rated for 50,000 hours. This represents over 11 years of continuous flowering.

Let’s say the LEDs last only 10 years (although they will last much longer):

HPS @ 10 years

Fixture cost 100 @ $ 450.00 = $ 45,000
Bulbs 1000 @ $ 75.00 = $ 75,000
Labor to change bulbs 1000 @ $ 20.00 = $ 20,000
Power – 21,900 hours @ $ .15 = $ 131,400
Total cost with HPS = $ 271,400

LED @ 10 years

Fixture cost 100 @ $ 899.00 – $ 89,900
Power - $ 65,700 @ .40 = $ 78,840
Total cost with LED = $ 168,740

Savings with with LED over ten years - $ 102,660 – or a savings of over 35% over HPS. Maybe a new Tesla?

You can argue with any of the specific figures in my example – but the moral of the story is the same. Assuming equal yield and plant quality, LEDs are much cheaper to operate than HPS.

Of course, this is a big IF - can a 600 watt LED actually get the same yield as a 1000-watt double ender?

In our experience, this is certainly possible, but not always easy. It depends a lot on the LED fixture as well as the style of growing. There is a huge boost by using spectrum control – this is discussed below.

The good news is that we keep getting more light out of a 600 watt LED with every new batch of LEDs – with no increase in cost. There may have been a gap in the past but we are at the tipping point now as far as real light output used by the plant.

It is very hard to argue that HPS will be the lighting technology of choice going forward or that this represents the best lighting investment long term.

In the most recent tests our latest LED has gotten better yield than a 1000 watt DE at an average actual power consumption of 650 watts - using advanced programmable spectrum control. Video and actual statistics to follow.

SPECTRUM – HPS IS GOOD FOR BLOOM BUT NOT IDEAL

Now we come to the weakest part of your post.

The major advantage of LED over HPS is spectrum. The HPS spectrum is fixed and always will be. LED spectrum is unlimited. This is the number one advantage of LED over HPS – not efficiency. Yet, you gloss right over this and talk about the level of blue from one bulb to another. Not so fast!

First, any grower knows that plants respond differently to different light spectrums. We could get into a very interesting discussion on light spectrum and plant growth, but I will save that for another day.

Many light technologies never worked well for plants due to their spectrum – incandescent and halogen never caught on as grow lights because their spectrum is wrong and they don’t work - inspite of their PPF ratings. HPS works great for bloom because it has a lot of high intensity red in the right spectrum, MH works well for veg because it has a lot of high intensity blue in the right spectrum, T5s are great for early veg as the have a lot of low intensity blue. But these are accidents! These ligths were never designed for plants. Much of the light produced by HPS and MH is not used at all or is absorbed by plants at a very low rate. Both technologies also put out huge amounts of heat which must be removed with even more energy.

LEDs are composed of emitters with very specific spectrums for very specific jobs. They can be tailored to any spectrum or power level for any application. This can even be varied over time. Therefore, LED is the most effective lighting technology for plants. No fixed spectrum light technology can make this claim.

If I was in the room at your lighting conference I would have stood up and talked on this subject for an hour. The HPS spectrum is inefficient when looking at chlorophyll absorption rates. We can do so much better! i would love to dive deeper into this subject in another thread.

VARIABLE SPECTRUM IS THE KEY

Variable spectrum in a single fixture offers additional advantages over any fixed spectrum light – HPS or even fixed spectrum LEDs. The spectrum of the sun varies over the day and over the seasons. Plants have evolved to best take advantage of this changing sunlight. they did not evolve under a single fixed spectrum. Understanding this and building a light that delivers it will give better results than any other lighting technology.

This is what we have done at California Lightworks – our mission is to free growers from stone age technologies, save the planet and grow incredible weed!

ENVIRONMENTAL IMPACT

As cannabis moves into the mainstream, there is a growing outcry from environmental groups regarding the huge energy waste in indoor growing – especially using HPS. Many states are offering significant rebates to encourage the shift to LEDs and away from HPS – and they should. This is the only planet we have.

What do we do with the HPS bulbs after they are used? They contain mercury and many of these bulbs end up in landfills contaminating our water and air supply.

We have seen several grass roots movements to ban HPS bulbs outright and this seems to be gathering steam.

LEDs represent a much more responsible solution to these issues.

In summary, Theo, I will make you a friendly wager. In five years, there will not even be a debate regarding the best grow light technology and you will no longer be selling HPS. A hundred bucks?

You seem like a bright guy and we are always looking for good sales and technical people at California Lightworks.

Thanks for stimulating this discussion!

Craig

[nicholas]

Thanks for the very in-depth posts @clones and @Theo. It’s clear you guys are both passionate about your work and very knowledgeable. The debate is very informative and shows off the pros and cons of both technologies.

Since this is the first time we’re having a vendor debate like this on the community, I wanted to hop in with a quick reminder of the rules of the ring. To avoid flamewars and things getting personal, we want to avoid any personal attacks and stick to the debating the technology. There hasn’t been anything you guys have said that is clearly over the line, but in my experience as a community manager it’s easy for people to get caught up in the heat of the moment. Thanks for keeping it professional and please continue to help educate the community on the respective merits of your products.

[CaliforniaLightworks]

Noted – just trying to liven up the conversation…

[Theo]

first of all (and I will respond in much more detail later) here are a few major flaws in your reasoning:

1. if you invest in LED now, in a year or two (or less), as you indicate yourself, the efficiency will me much higher. If you reason that you are going to use your fixture for ten years, you will be looking at using fixtures that in a few years probably use 20-35% more energy than what is current because technology has advanced and your light has depreciated.
2. The spectrum of the sun does not change over seasons. It does change during sunrise and sunset, and slightly during overcast.
3. I totally disagree with your argument of huge energy waste. This would only apply if LED fixtures would be much more efficient, and they are not at the moment.
4. The industry will move more to a greenhouse type of cultivation, as indoor rooms are not a sensible choice and do waste lots of energy. In the coming years you will see a lot of hybrid lighting, as you will see in orticulture.

It may seem like I am an “LED hater” and fight for HPS: That I do not. I love LED, but in horticulture in most types of grows it is still impossible to calculate a break even point with HPS on short term and for some crops it is not even a valid option at this moment because of the lack of IR from the LED fixtures.

If LED would be viable, wouldn’t you think that horticulture in particular would have already moved en masse to LED?

I will share some calculations with you later. I am looking forward to see PPF specs on your fixtures.

[nicholas]

@clones

Noted – just trying to liven up the conversation…

Thanks, I appreciate the understanding. By all means keep the conversation lively - I don’t want to stop you guys debating the merits of the technology!

[Hunter]

I’m enjoying the debate guys! Keep it friendly.

To your point @Theo about IR spectrum, there are some LED lights that emit in the IR spectrum (it depends on what material the semiconductor is), but I can’t say whether or not they’re being included in commercial LED grow fixtures. That’s something for @clones to answer.

[Theo]

Infrared comes in many forms. I suppose you mean far red, 730 nm. What I am talking about is more the longer wavelength infrared, the heat radiation. LEDs by definition do not emit heat at the front, but at the back.

[Theo]

So here is a calculation. Given a fixture that has the same output as a 1000W lamp, and the same efficiency, because I do not believe or see that a 600W LED has the same output as a 1000W HPS fixture. So that is already making a big assumption. To make it more comparable, I have included HPS + plasma, which has the big advantage of also adding UVA and UVB (LED fixtures that claim to have UV mostly have 380 nm, hardly any functional UV). I took the retail prices (Growershouse) to compare the two, and calculate what the fixture would cost you if you write it off over 1 year to five years, to see where they break even.

Then let us assume that the LED fixture is 10% more efficient:

I’m not calculating even interest, current present value etc. I replace lamp AND reflector each year and included labor for that. I took an average electricity price but I can fill in any value of course.

The up front costs are 4 times as high with LED, so that has a considerable impact on the investment costs. I calculated, based on the total costs, the price per umol, to be able to compare the two technologies.

In our opinion price needs to come down, and efficiency needs to go up to become a viable replacement of HPS. In many environments we believe a mix of HPS and LED will be a future solution, specifically in greenhouses, where you have a maximum natural cooling capacity, so if you go beyond 300 umol m-2 s-1 you will need additional cooling, HPS is beneficial there because we know that an average full LED greenhouse uses 15% more energy on heating the crop (already using lots of rest heatfrom the own energy production).

Then there is another issue. At lower PPFD the yield per W invested energy is higher than at high PPFD. That means you get more yield per Watt invested, but NOT per square meter, and this is what defines your profitability. I see lots of people reporting high yields PER WATT, and of course that is natural and true. The higher you get to the saturation point, the less influence adding more light has. So going from 500 umol m-1 s-1 to 1000 umol m-2 s-1 will not give you 100% more yield. But it will give you 30, or even 40% when you add CO2 extra. That easily pays for the energy you put in it, be it LED or HPS.

It’s an interesting discussion. But again, I am not against LED. We have been making LED fixtures for years, just not for horticultural top light solutions. We produce a great aquatics light, iphone controlled, WiFi, fully automatic for example.

We will come with LED fixtures, for sure. Until now however we did not see that the time was right to launch one in horticulture. We can not justify the investment to the grower and believe me, Philips is all about LED at the moment, they are investing millions into it and provide even financing to get the projects going. And for many projects, such as multi layer, research, lettuce etc. you may be able to build a long term case given the right price.

But again, when are you going to get on board of the LED wagon? At what price and efficiency, because LED is still a maturing technology and there is a lot of efficiency to be gained still. Choosing LED now means that you will have to stick with your investment for a long while. I refer you to the specs of respectable LED manufacturers.

[nicholas]

@theo the images you uploaded appear to be a bit small for the text to be read. Do you have larger versions of those images? If you need assistance with the upload I’m happy to help.

[Theo]

I’m sorry the pictures are a bit low resolution, that’s a forum limitation. Here is the PDF

led vs hps.pdf (97.3 KB)

[nicholas]

Thanks, the PDF is more readable. For anyone clicking on the link, it defaults to download rather than opening in a new tab, so you’ll need to open up the file after you’ve downloaded it.

Also, @theo it should let you upload images up to 10MB, and anything that is larger than the space of the post will create a thumbnail version that will expand when you click on it. If you’re having any issues with image uploads let me know and I can help get it sorted out.

[Hunter]

Great charts @Theo! What’s your thought on the spectrum argument though?

For comparison, here’s a few charts of the absorption spectra of the different pigments found in most plants:

Here’s a typical HPS emission spectrum:

@clones argument seems to be that you’re missing a huge portion of the chlorophyll/carotene spectrum, and putting in a lot of light in an unused section. What say you?

[Theo]

About your invitation, forgot about that:

@clones

You seem like a bright guy and we are always looking for good sales and technical people at California Lightworks.

Thanks but I don’t think you can afford me ;).

I would be happy already if you can provide me the PPF of your 400W fixtures equipped with Osram LEDs. We are very familiar with those LEDs, we use them as well.

[Theo]

@Hunter

What’s your thought on the spectrum argument though?

Well, the thing is, in horticultural research we already found out that photosynthesis is not so much influenced by spectrum directly. Of course there are minimum requirements to a spectrum and HPS is far from full. I refer to Bruce Bugbee’s experiment with different lightsources, from LPS to incandescent, and there was hardly any difference in photosynthesis. The big difference however is morphogenesis, which can result in gain on gain. So yes, you can grow a different plant under a wider spectrum light and it will stay a lot healthier under that light.

Of course we already know the beneficial effects of UV, and there is also a minimum of blue light you should have for a healthy crop. What if I were to say to you that I believe that in full spectrum high intensity light green light is more efficient than red and blue light?

There is still so much we don’t know, but we do know one thing: The spectrum of the sun never shifts. We know that we can manipulate a plant with different spectra. We can make it shorter with lots of blue light, and there is where LEDs come in handy, or make the plant stretch with just a little bit of far red light. We can make it more open with green light, and get better leaf positioning in a combination with blue.

It would be good to realize that the scientific community is still experimenting with light recipes for different crops, and we are very lucky that this industry is here solely by the virtue of a plant which in fact does quite well under this HPS spectrum.

[Theo]

Before we are going to discuss all lighting, let us stay on topic for a bit.

My point is: I take offense in how many LED manufacturers do their marketing and try to mislead the customer by not providing basic information.

I would very much like to see a situation such as in professional horticulture, where we do all share these specs.

I want to warn you against false information and misleading half-truths. I am not an LED hater, I just hate misleading marketing.