LED Grow lights

Science
#18

LED spectral width (point at which lower power values are less than 50% of peak value) is typically 50 to more than 100 nm. That is, you won’t really see a ‘line’ rather a distribution centered on the stated LED frequency. (in contrast to a laser or laser diode that has a spectral width of maybe less than one nm).

Thus, when you mix a few LEDs of close frequency, you need a spectrophotometer to really see the net spectral power. You could sort of calculate the spectum, knowing all the LEDs and the powers and the angles, etc, but with the uncertainty of all the variables and whether you are really getting what you think you are getting, the photometer gives you the flux at the level of the exposure area.

I think it is probably wishful thinking to actually get such an instrument. They are really expensive and the money would probably be better spent on other things. Unless we found one on ebay.

But if we got serious and developed a product and wanted to make a bunch, it would be cool to have.

#19

I started googling it, and you’re right. It’s not nearly as spiky as I figured it’d be.

#20

Gentlemen,

I have recently used a spectrophotometer in my Biology lab and it is sourced from an educational products company which offers it at a relatively attractive price point and will give you a graphical wavelength distribution.

http://www.vernier.com/products/sensors/spectrometers/visible-range/svis-pl/

It runs about $470 and for measuring light emissions spectra, you also need an optical fiber adapter for $70. (+ tax and shipping)

The slight catch is that you also need a LabQuest interface and the LoggerPro software, (another $320 - $575 depending on the interface) but I already own both as I have been using Vernier sensor array products for over 12 years.

Let me know if you are interested.

380 nm–950 nm Wavelength reporting interval ~1 nm Optical resolution* 4.0 nm (at 656 nm) 25 nm (at 486 nm)

Wavelength accuracy† ± 3.0 nm (at 650 nm) ± 7.0 nm (at 450 nm)
Photometric accuracy‡ ± 13.0%
Typical scan time ~ 2 s Operating temperature 15–35ºC

BTW, they do have an even more accurate model that is specifically designed for light emissions, but it runs about $230 extra.

-JAG

#21

Thanks, JAG, that would not be a bad deal if we get to that point.

Do you know if your program or the instrument allows one to make measurements in micromoles of photons per square meter per second or some equivalent measurement of photon flux. That is the sort of ‘gold standard’ for measurement for photosynthetically active radiation (PAR) from a grow light.

I’ll look for a reference for this.

Here is a guy doing quantitative measurment.

Ultimately, we would want to be able to not only get the ‘curve’ but do the quantitative measurement as they are doing. Once again, I’m getting way ahead of things here because we need to determine the LED wavelengths we want and then source them based on reliability, form factor, drive voltage, power and lumens per watt efficiency.

Ideally -

reliability - long life
form factor - the same or close enough so we could heat sink them all on the same heat sink
drive voltage - hope to use the same voltages and / or driver circuit(s)
power - higher better - I’d say 3W minimum and maybe 5 watt units (this is what the others do)
efficiency - optimize lumens per watt
viewing angle - need close to the same angular intensity distribution

These are just my own ideas. I’m not an expert on it and have never built one so feel free to comment with your own ideas.

#22

Mr. David Jackson,

Thanks, JAG, that would not be a bad deal if we get to that point.
Do you know if your program or the instrument allows one to make
measurements in micromoles of photons per square meter per second or
some equivalent measurement of photon flux. That is the sort of ‘gold
standard’ for measurement for photosynthetically active radiation (PAR)
from a grow light.

Yes it does with another sensor that runs about $190.

And you can even cross correlate effects with other sensors: (CO2 sensor - I’ve used this one as well)

Joel-Anthony Gray

#23

Interesting. That seems close to what we need. I sent the guy a question. Look at the specs on the sensor and tell me if this makes sense:

I have a question about your PAR sensor. I watched the video and download the pdf spec sheet. You say it is sensitive to the PAR of the light spectrum.

“The sensor responds to visible light in the spectral
range that is used by plants in photosynthesis (400–700 nm).”

However, green light is specifically in the middle of the sensitivity range for your PAR sensor, around 530. See figure 1 at

Thus, a green light would show up on your PAR sensor as having plenty of PAR and yet this color should not be in the PAR.

How does the spectral sensitivity curve of your sensor support the claim to be sensitive only to the PAR?

#24

David,

Thus, a green light would show up on your PAR sensor as having plenty of PAR and yet this color should not be in the PAR. How does the spectral sensitivity curve of your sensor support the claim to be sensitive only to the PAR?

That is an understandable question as we are used to green leaves and grass, etc. But plants have other photosynthetic pigmentations other than Chlorophyll a and b.

As you can see, the entire spectrum of 400 - 700 can be potentially weighted as far as a plant converting light to chemical energy, depending on the mixture of pigments. Also, charts on these pigments differ from once source to another and I have seen beta-carotene extend somewhat past 532 nm green. Even the absorption percentages vary depending on the reference you consult - some drop it down to nearly 0 % at the green wavelengths, others show at least 10-15 %.

Ultimately what matters is what plant you are using and the CO2 sensor diagram from my previous post illustrates a good way to experiment with the optimal plant respiration wavelengths you are looking for.

I found this diagram interesting as well as it appears to weight numerous pigment wavelength responses simultaneously and add them up into the green “Output from photosynthesis” line which again covers the entire 400 - 700 nm wavelength.

From a technical perspective, I don’t see it as easy or even desirable to make a PAR sensor that selectively notches out certain wavelengths. Just looking at the curves, they are never just one simple peak and are at least bi-modal and not cleanly linear which complicates the formula along with more than one pigment being present. In my mind it is easier to use an optical filter over the light or to re-calibrate / post-process the data to fit the curves for the plant you are using more accurately.

Also the PAR sensor does have some calibration adjustment for electric lights vs. sunlight as you may have noticed.

-JAG

#25

You all seem to have done quite a bit of research. Can anyone explain to me whether lumens really matter? I have seen people on YouTube claim that it does and others that claim that it does not.

-Sebron

#26

JAG, thanks for more great info. Hope to talk about it soon.

Sebron,

Certainly lumens matter. But the PAR assay for grow lights helps to distinguish ‘quality lumens’ that are more beneficial to the plants. For instance, if you had two grow lights and they both had roughly equivalent spectrum, then more lumens = better.

I have seen at least one seller that does not quote any lumen information nor other spectral info and simply states that his lights are proven the ‘best’ and he specifically says he won’t provide that info because it is not useful. I either feel like he is hiding something or thinks that the rest of us cannot make sense of the data and either way I don’t feel comfortable buying that product.

#27

Here is the response I got re my question above to the vernier company:

Plant Physiologists have defined PAR as all of the wavelength across this range. The sensor responds equally to all quanta of light across the visible range, from 400-700 nm. The sensor head of the sensor is an Apogee Sensors PAR sensor.

You might be thinking of Yield Photon Flux. The Vernier PAR Sensor can be used to measure yield photon flux density (YPFD or YPF) - which is expressed in units of micromoles m-2 s-1, but is based on the ‘true’ photosynthetic action spectrum of plants.

Thus, YPFD is a more accurate measure of the amount of light available for photosynthesis.

However, PPFD (units for PAR) is simpler to define and is a more widely accepted measurement in the field of plant physiology.

To measure YPFD in sunlight the slope of the calibration equation needs to be decreased by 10% (from 500 to 450). To measure the YPFD from electric lights the slope of the calibration equation needs to be decreased by 11% (from 500 to 445). See the instructions above on how to adjust the slope calibration equation of the PAR Sensor that are located in the Specifications and User Guide included with each unit.

There are also specific adjustments that can be made to the calibration equation for different light types to make it even more accurate.

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#28

Hey guys, just wanted to let you all know that the Electronics committee is looking at a few new meters and scopes they’re wanting to buy–apparently there is interest over there to get a Spectrophotometer as well. I suggested that if this is something that would be beneficial to both committees that we may want to combine our efforts. I doubt that anyone will be using it so much to where we couldn’t share it. They want one for pretty much the same reason we do–to verify sourced LEDs for various lighting projects.

Feel free to hop over and chime in, especially Andrew, as such collaboration will likely need both committee chairs.

#29

JAG would be the one to ask about photometry. He may have some software that would otherwise have to be purchased. I responded to the guy from Vernier and asked exactly what we would need to make the measurements we want. I await his reply and will let you know what he says.

BTW, I want to set up a sort of mini electronics lab in the Bio area. I have a surplus of some decent equipment (scope, power supplies, meters, parts) and I would be willing to supply these although we have a problem with space. This brings up another idea. A sort of satellite electronics area might not be such a terrible idea. The Bio elect lab would be an option for this if we could find some space, say, in the shop area not too far from Bio. It could be used by anyone with a need just as we share the printers. I have seen folks bring equipment to other areas like the class rooms and do testing and development there.

The focus of this satellite area would be embedded processors / sensors / actuators. I have in mind PIC processors, Arduino and RPi but others would be welcome.

#30

@rice81 Why would you not want to use space in the electronics lab? I’m still new to the space, but I was under the impression that all work areas were accessible to everyone.

#31

No reason except as a matter of convenience. We have some things planned in the bio area with sensors and automation at some point. I’ll probably just bring in some of my equipment rather than drag elec lab stuff over to bio. Meanwhile, if I brought equipment and we had the space, I wouldn’t mind anyone else using it in the area if that was more convenient than the elec lab.

But you are correct, I believe. I’m still a bit new and except for equipment and areas that need safety and other training (wood shop, mill / lathe, 3D printers, large scale printer and maybe others) all is open to all members.

#32

Clayton,

Why would you not want to use space in the electronics lab? I’m still
new to the space, but I was under the impression that all work areas
were accessible to everyone.

A sensible question and one that I have a definitive take on:

Yes, there is space in the electronics lab, but sometimes it is in heavier use than other areas and there has been several instances where I had a project set up to work on (such as putting a 3D printer together) in the warehouse and it is a real pain to have to run back and forth gathering a soldering iron, solder, flux, wire, etc.

David, I would like to propose that the mini-space be a moveable cart that has commonly used items in electronics fabrication/repair so that it can be wheeled to wherever someone needs it. As long as the tools are clearly labeled as belonging to the cart, it could minimize running back and forth. (and reduce the chance of not returning a tool to the electronics lab where it belongs)

Probably a two tier model with drawers and a tabletop workspace would be ideal.

Thank you for the kudos, BTW. Also to clarify, I definitively do have the software and could at least temporarily supply an interface. I have thought about upgrading to the LabQuest Mark II, so perhaps some kind of deal could be struck that would benefit everyone. I am a strong proponent of the Vernier system as they have over 70 different types of sensors, can interface with Arduino, Palm, and National Instruments, and I like the fact that you can track up to 6 sensors (2 digital, 4 analog) simultaneously with the option of a Digital Control Unit which can be programmed to trigger a voltage in case of an event.

And being an educational company, they have a number of ready to go experiments, workbooks and a quarterly applications newsletter. Perhaps I should bring a catalog up there for you to peruse through. They cover everything from Human Physiology to Physics and Environmental Science, so it is a versatile platform.

Joel-Anthony Gray

#33

A shared electronics cart would work well for my vision for the Laser Department, also. I am trying to encourage the expansion of the Laser Department to include a wide range of types of lasers and uses of these lasers, as well as experimentation and use of optical sensors.

1 Like
#34

Joel,

I really like the idea of a moveable electronics cart. That’s a great idea. I’ll give it some thought.

BTW, sorrry to sort of hijack this LED thread. If I knew how and had privileges, I believe it could be split into a separate thread on the electronics cart idea.

DJ

#35

One of us could simply start a new thread, perhaps in the general DMS area, letting the other groups know of our proposal.

#36

This has already picked up interest in another thread…both the LEDs and I think the cart and shared electronics as well…

Continuing the discussion from Equipment for electronics lab:

#37

Richard and Everyone,

One of us could simply start a new thread, perhaps in the general DMS area, letting the other groups know of our proposal.

Done.

JAG