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.
How should a light/lamp/fixture be specified?
Basically there are only four specs that really matter:
- Power use
- Light maintenance.
In this post I am just going to touch the basics.
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)
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.
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.
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.
- There is no magic spectrum that performs 30, or even 10% better as in photosynthesis and yield
- There is no magic lamp that performs 50, or even 30% more efficient than HPS
- 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!