Engineering Student Efficient Lighting Assistance

Hello,

First let me say a huge thank you to everyone who posts here for the wealth of valuable information they share. You guys and gals have an awesome community. I specifically want to thank @SupraSPL and @alesh, as their previous posts have provided me with tons of useful information.

Second, I've been scouring these forums for a while now because I'm currently a senior studying Mechanical Engineering and our project is to create a fully automated growing environment. Unfortunately, I don't go to school in one of the more progressive states, so we're stuck growing lettuce for now

Due to multiple project constraints we've decided to shoot for a PPFD of 150 umol/m^2-sec or, to be more clear, a DLI of 13. Although this light may seem low, our hope is to supplement CO2 at approximately 1000ppm to achieve similar results to this study.

http://www.cornellcea.com/attachments/CO2 and lettuce.pdf

Our system needs to light a space of approximately 8ft^2 (.743m^2), from approximately 1 foot above the canopy (possibly lower if necessary)...the catch is that it needs to be done for under 57.14 Watts.

I was lucky enough to stumble upon @alesh 's incredible post here:

https://www.rollitup.org/t/math-behind.868988/

and have been trying to wrap my head around the best way to approach this problem:

I'm thinking that I might be able to calculate the umol/J, multiply by the input watts to get PPF, and convert the PPFD to my area to get an accurate estimate.

For example:

If we take a full spectrum LED with 4.66 umol/J and drive it with 30 watts we would get 4.66 x 30 = 139.8umol/s of photons radiated from the light.

Now, I would guess that I have to assume about half of these photons actually got dissipated as heat? So that would only leave me with 69.9umol/s flying towards the canopy.

If I assume a height of approximately 1 foot above the canopy, and I want to cover a 2 foot by 2 foot wide area as well as possible, this would give me a necessary beam angle of 90 degrees. (I solved this elsewhere but can attach if desired).

So now I basically have all 69.9umol/s of my photons spread out over a 4ft^2 area (2ft x 2ft). If I divide by 4, this gives me a PPFD of 17.475 umol/ft^2-sec

Or, in a more familiar PPFD unit | 189.94 umol/m^2-sec

Everything looks good so far, except for the fact that I need to cover a 8ft^2 area (2ft x 4ft) which means I would need 2 of these LED's. This would put me at 60 watts, above my desired 57.14 Watts design constraint. Also, I have a hunch that the 189.94 umol/m^2-sec number I solved would be an average over the area (with directly under the light reaching around 300umol/m^2-sec and the edges maybe not even hitting 125umol/m^2-sec? These calculations also didn't take into account efficiency loss associated with the driver.

So finally, to my questions.

1. At the very least, does this seem like a decent process to try and make lighting design decisions?

2. Have I made any sort of major assumption errors here that would drastically throw off my estimates?

3. This whole design process hinges on having the umol/J number which takes a considerable amount of work (although @alesh has made this work much easier). I simply don't have time to compare all available LED's to find the most efficient/best one for my constraints. Is there a umol/J list for different LED's floating around anywhere that I could use to test against my constraints? This would be an absolute lifesaver.

4. Is what I'm trying to do even possible?

Thanks tremendously and I look forward to hearing any opinions or suggestions you guys/gals might have.

-Chase

i dont see cost in your budget. i get that its a university study but not considering cost is erroneous. you can probably achieve any of your flux goals by throwing money at it but thats not what engineering is about

Welcome:... sorry to say japanese 13yo students have beat you to the punch already

from above, lettuce does very well with your standard flouro's in the 6500 kelvin range

thats shop lights, (T*/T5) at a max of 2 inches above the top most leaf, they love heat at about 25c/77f

with high humidity, and C02 is totally unnecessary, as the only 'real' advantage is you can blast plants

with more lux, under higher temps with a slight increase in photo activity

select a plant similar to weed like Hops..? that like weed loves that light and can work under C02

with ok results

consider putting your hard earned efforts into guiding the membership into a DIY COB

thats gives good results at minimal cost

good luck

@CobKits - Thanks for the response. Was actually just on your site. Of course the budget is a constraint, budget is always a constraint. For the above listed goal, and with our current small sponsorship, we're trying to keep the lighting portion to approximately $70 but may be able to go as high as $100. Obviously the less spent the better. Thanks for your input and we'd love to hear any suggestions you have.

@vostok - I know we're not the first people to do something like this and likely won't be the last. Regardless, we're viewing it as a learning experience. The automated part of the project is what we really hope to sink our teeth into. I'd rather not use T5's (the non LED versions that is) as I know they're not very efficient.

As for the statement that blasting plants with CO2 only has an effect with increased light levels... the study I posted actually showed that you can compensate for decreased light levels with extra CO2.

Because we're trying to keep energy usage as low as possible, and because we're very aware of budget (@CobKits, CO2 is much cheaper than KWh's), we're going to give this gamble a try.

As far as DIY COB's, I'm very into that idea, just trying to learn where to go to get the best information and actually do the math. Would like to compare the COB numbers with some smaller LED numbers to see what ends up being more efficient/cost effective. All opinions welcome!

Thanks again for both of your responses!

-Chase

cbrum11 said:

@CobKits - Thanks for the response. Was actually just on your site. Of course the budget is a constraint, budget is always a constraint. For the above listed goal, and with our current small sponsorship, we're trying to keep the lighting portion to approximately $70 but may be able to go as high as $100. Obviously the less spent the better. Thanks for your input and we'd love to hear any suggestions you have.

Click to expand...

well i understand your constraints but am just saying.. as far as horticulture under artificial lighting its been done. you need to offer the angle of economics to your study if its going to be useful

cbrum11 said:

CO2 is much cheaper than KWh's

Click to expand...

gimme a well-to-wheel analysis of your average guy driving to the store to pick up a tank and its resulting cost savings vs $0.10/KWh electricity

https://www.rollitup.org/t/diy-cob-led-calculator.890214/

cbrum11 said:

Hello,

First let me say a huge thank you to everyone who posts here for the wealth of valuable information they share. You guys and gals have an awesome community. I specifically want to thank @SupraSPL and @alesh, as their previous posts have provided me with tons of useful information.

Second, I've been scouring these forums for a while now because I'm currently a senior studying Mechanical Engineering and our project is to create a fully automated growing environment. Unfortunately, I don't go to school in one of the more progressive states, so we're stuck growing lettuce for now

Due to multiple project constraints we've decided to shoot for a PPFD of 150 umol/m^2-sec or, to be more clear, a DLI of 13. Although this light may seem low, our hope is to supplement CO2 at approximately 1000ppm to achieve similar results to this study.

http://www.cornellcea.com/attachments/CO2 and lettuce.pdf

Our system needs to light a space of approximately 8ft^2 (.743m^2), from approximately 1 foot above the canopy (possibly lower if necessary)...the catch is that it needs to be done for under 57.14 Watts.

I was lucky enough to stumble upon @alesh 's incredible post here:

https://www.rollitup.org/t/math-behind.868988/

and have been trying to wrap my head around the best way to approach this problem:

I'm thinking that I might be able to calculate the umol/J, multiply by the input watts to get PPF, and convert the PPFD to my area to get an accurate estimate.

For example:

If we take a full spectrum LED with 4.66 umol/J and drive it with 30 watts we would get 4.66 x 30 = 139.8umol/s of photons radiated from the light.

Now, I would guess that I have to assume about half of these photons actually got dissipated as heat? So that would only leave me with 69.9umol/s flying towards the canopy.

If I assume a height of approximately 1 foot above the canopy, and I want to cover a 2 foot by 2 foot wide area as well as possible, this would give me a necessary beam angle of 90 degrees. (I solved this elsewhere but can attach if desired).

So now I basically have all 69.9umol/s of my photons spread out over a 4ft^2 area (2ft x 2ft). If I divide by 4, this gives me a PPFD of 17.475 umol/ft^2-sec

Or, in a more familiar PPFD unit | 189.94 umol/m^2-sec

Everything looks good so far, except for the fact that I need to cover a 8ft^2 area (2ft x 4ft) which means I would need 2 of these LED's. This would put me at 60 watts, above my desired 57.14 Watts design constraint. Also, I have a hunch that the 189.94 umol/m^2-sec number I solved would be an average over the area (with directly under the light reaching around 300umol/m^2-sec and the edges maybe not even hitting 125umol/m^2-sec? These calculations also didn't take into account efficiency loss associated with the driver.

So finally, to my questions.

1. At the very least, does this seem like a decent process to try and make lighting design decisions?

2. Have I made any sort of major assumption errors here that would drastically throw off my estimates?

3. This whole design process hinges on having the umol/J number which takes a considerable amount of work (although @alesh has made this work much easier). I simply don't have time to compare all available LED's to find the most efficient/best one for my constraints. Is there a umol/J list for different LED's floating around anywhere that I could use to test against my constraints? This would be an absolute lifesaver.

4. Is what I'm trying to do even possible?

Thanks tremendously and I look forward to hearing any opinions or suggestions you guys/gals might have.

-Chase

Click to expand...

Thanks @nogod_

Just briefly playing around with the calculator, it looks like what I would like to do is very possible. Maybe even for much lower Watts than I thought! My only concern now is having significant hot spots if I go with COB's instead of a bunch of smaller LED's.

Anyone suggestions on this front? Or links to PPFD maps for specific COBS?

If maps aren't available, is it a fair thing to take the beam angle graphs within the CREE datasheets and just do some simple math? The parabolic looking graphs that graph beam vs. percent?

Page 8 here: http://www.cree.com/~/media/Files/Cree/LED-Components-and-Modules/XLamp/Data-and-Binning/ds-CXA3070.pdf)

For example, let's say that COB put out 200 umol/m^2-sec (it doesn't but I'm just using an easy number). Would it put that out directly underneath it, and, if no lens were used, only put out 60% of that ( 200 x .6 = 120 umol/m^2-sec) at the location on my canopy at an angle of +- 50 degrees from the center?

Thanks again for all your help.

-Chase

@CobKits - The total system is assumed to run at about 500 Watts for a 7 week growing cycle.

500 Watts x 24 hours per day x 7 days a week x 7 weeks = 588 KWh

Let's say by supplementing CO2 to 1000ppm we can decrease total system Watts to 300 Watts per 7 week growing cycle and achieve equal growth.

300 Watts x 24 hours per day x 7 days a week x 7 weeks = 352.8 KWh

588 - 352.8 = 235.2 KWh Saved

At your price of 0.10 per KWh | 235.2 x .10 = $23.50 energy cost

I won't go into full CO2 details because it's getting late, but my calculations say a 5 lb bottle (apprx $15.00) should last at least 1 growing cycle.

23.50 - 15.00 = $8.50 savings every 7 weeks in choosing to supplement with CO2 instead of going with stronger lights.

I admit @CobKits ... not near as attractive as I first thought. However, the savings do grow in areas that have higher energy costs. Savings would also increase if I could get the lighting watts even lower by switching, 300 Watts was just a guess. Would have thought it would have been a lot more though, that's for sure.

If anyone see's errors with my calculations, please let me know.

Thanks,
-Chase

cbrum11 said:

For example:

If we take a full spectrum LED with 4.66 umol/J and drive it with 30 watts we would get 4.66 x 30 = 139.8umol/s of photons radiated from the light.

Now, I would guess that I have to assume about half of these photons actually got dissipated as heat? So that would only leave me with 69.9umol/s flying towards the canopy.

Click to expand...

These values, QER, are property of a spectrum. Meaning that each radiated joule from the LED is equal to whatever the value is for your spectrum of photons. Electrical efficiency (ratio of energy radiated and dissipated) is another story.

If your space is vertically restricted, smaller single-die LEDs might be a better choice for you. Or COBs with wide angle street light (batwing) optics.

To reach DLI of 13 in your setup (8 sqft & 24 h on light period), I'd say you need, considering all the losses, about 150 µmol/s at LED level. With maximum power dissipation of 57W, you need to choose LEDs that would be able to produce 2.6 µmol/J at LED level.

Just take 4 1212s and run them around 12w each at about ~18-24" above.

Or grab a bunch of used, discarded, chinese burple and other assorted panels and hook them all up to 1 50w driver. As long as they turn on, they will give you photons.

CobKits said:

gimme a well-to-wheel analysis of your average guy driving to the store to pick up a tank and its resulting cost savings vs $0.10/KWh electricity

Click to expand...

Already on an existing delivery route or there is a local supply that needs it discarded as a waste by product.

Don't let this get into energy credit cap and trade talk.

Look into smd strips or something like the hard strips from cutter<link.

Many ways to skin this cat, at this point I think you have enough tools to D....I.....Y.

cbrum11 said:

Thanks @nogod_

Just briefly playing around with the calculator, it looks like what I would like to do is very possible. Maybe even for much lower Watts than I thought! My only concern now is having significant hot spots if I go with COB's instead of a bunch of smaller LED's.

Anyone suggestions on this front? Or links to PPFD maps for specific COBS?

If maps aren't available, is it a fair thing to take the beam angle graphs within the CREE datasheets and just do some simple math? The parabolic looking graphs that graph beam vs. percent?

Page 8 here: http://www.cree.com/~/media/Files/Cree/LED-Components-and-Modules/XLamp/Data-and-Binning/ds-CXA3070.pdf)

For example, let's say that COB put out 200 umol/m^2-sec (it doesn't but I'm just using an easy number). Would it put that out directly underneath it, and, if no lens were used, only put out 60% of that ( 200 x .6 = 120 umol/m^2-sec) at the location on my canopy at an angle of +- 50 degrees from the center?

Thanks again for all your help.

-Chase

Click to expand...

Hi Chase,

If we can come to a meeting of the minds, I am interested in sponsoring your project with free materials, design ideas and more. (Ron, CEO, fasterharvest.com) In return, I would want access to your results.

cbrum11 said:

our project is to create a fully automated growing environment.

Click to expand...

This implies much more than lighting... for sure would include:
1) Automated nutrient supply.
2) Climate control.

If by "fully automated growing environment", the prof means "fully automated growing environment system"... then it would include robotics to go fully automated from seed to packaged product.
(I have ideas for this too.)

If "fully automated growing environment" is your only stated primary objective, I think you are under the false assumption that you must have artificial lighting. Options could be natural lighting, artificial lighting and supplemental lighting (a combo of both).

cbrum11 said:

Due to multiple project constraints

Click to expand...

Can you please give us a list of those constraints?

Also, what is the judging criteria?
ie (percentage of automation), (plant mass produced), (cost per gram of plant mass produced) etc

Are you actually going to have to build what you design?

cbrum11 said:

http://www.cornellcea.com/attachments/CO2 and lettuce.pdf

Click to expand...

Many commercial environments need supplemental heat during a portion of the year. Consider using the waste CO2 during these times. This will lower your carbon footprint while increasing growth.

cbrum11 said:

Our system needs to light a space of approximately 8ft^2 (.743m^2), from approximately 1 foot above the canopy (possibly lower if necessary)...the catch is that it needs to be done for under 57.14 Watts.

Click to expand...

I can provide at least three options.

cbrum11 said:

I was lucky enough to stumble upon @alesh 's incredible post here:
https://www.rollitup.org/t/math-behind.868988/
and have been trying to wrap my head around the best way to approach this problem:

Click to expand...

My advice is to not fall into the "McCree Curve" black hole. The McCree Curve was never intended to be used as a method to select artificial lighting. In a nutshell, McCree studied very limited bandwidths of light (in the absence of other bands) and determined that red was the most efficient of these limited bandwidths. McCree does NOT consider combined bandwidths.
Other studies have shown that 1) 50% blue combined with red produces more and 2) up to 24% green will improve growth and over that is ignored.
In my opinion, the DIN is a better measurement of "grow power"... but even DIN is flawed. I don't know of anything better... and in general, studies are lacking.

cbrum11 said:

I'm thinking that I might be able to calculate the umol/J, multiply by the input watts to get PPF, and convert the PPFD to my area to get an accurate estimate.

Click to expand...

Considering only PPF/PPFD is only part of the equation to find the best grow light. For instance, our green lamp has a high PPF/PPFD, but since much of green light is reflected by most plants... it is highly doubtful that the green lamp alone will achieve high growth.

cbrum11 said:

1. At the very least, does this seem like a decent process to try and make lighting design decisions?

Click to expand...

In my way of thinking, you are putting way too much time and energy into lighting design. Keep it simple and use off-the-shelf lighting. You would be wise to concentrate more of your efforts into the other aspects of your "automated growing environment". Again, I have many ideas and some current products.

My company is slowly working towards a "cost effective semi-automated growing environment system" ... most normally used for leafy greens... and I think we might be able to help each other. If interested to explore this conversation further, please contact me directly.

Thanks,
Ron