LED vs. HPS: Truth about photosynthetic eff. & uniformity

Beta Test Team · Nov 21, 2014

[NOTE #1: The original thread title ("LED vs. HPS: A reality check") was from the first PDF below. But a few LED growers got mad at the title, so to try to keep the thread on-topic I changed the title - but not the content]

[NOTE #2: I added the following sentence to this post to try and keep this thread on-topic: "This thread is about the photosynthetic efficiency of luminaries, and their irradiance uniformity, that is, converting watts into photosynthetic photons and the uniformity of the footprint."]

This thread is about the photosynthetic efficiency of luminaries, and their irradiance uniformity. That is, converting watts into photosynthetic photons and the uniformity of the footprint.

This research includes some interesting data on the efficiency of LEDs vs. HID in terms of converting watts (j/s) into flux (umol/s, that is, photosynthetic photon output). The main metric is efficiency defined as photosynthetic umol/J.

When accounting for most LED price points, and lowish umol/s per joule compared to HPS, many LED brands may not be as efficient and powerful as their makers tend to claim, and the same goes for HID luminaires.

None of this is to say LEDs aren't great technology, it is, but it does suggest the way they're used make a huge difference in their efficiency and worth as compared to HID. In other words, for large grows of high irradiance plants, LEDs are not as efficient they're often claimed (when accounting for price, etc.).

Here's a short report by Dr. Runkle, Dr. Nelson, and Dr. Bugbee:
http://www.gpnmag.com/sites/default/files/14_TechnicallySpeaking_GPN0614.pdf

And another by Dr. Nelson and Dr. Bugbee:
http://cpl.usu.edu/files/publications/poster/pub__9913943.pdf

And here's the source material, a published study (April, 2014) by Dr. Nelson and Dr. Bugbee:

Economic Analysis of Greenhouse Lighting: Light Emitting Diodes vs. High Intensity Discharge Fixtures
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0099010

Beta Test Team · Nov 21, 2014

Here is interesting data from that 2014 study:

NOTE #1: The pricing info for some brands may be old, such as Cycloptics is old, the price is $420 per unit now.

NOTE #2: This study was about greenhouses, so it doesn't take wall or ceiling reflectivity into account, nor over-lapping irradiance from multiple lamps or LEDs, when listing photosynthetic umols. Therefore it's of limited value for indoor or growth chambers.

Note #3: These data were collected with an integrating sphere into which a single reflector or LED array was placed.

NOTE #4: This study was about efficiency in terms of turning watts (j/s) into photosynthetic umol (photons within 400-700 nm band). Therefore, again, these data need to be seen in that light (no pun intended).

NOTE #5: The pricing is by MSRP, and volume discount can reduce the sale price per unit considerably.

Beta Test Team · Nov 21, 2014

If we look at the two most efficient luminaires studied, the 1000W Gavita Pro DE, and the Light Science Grow Advantage Violet LED, we see that the wattage of the Gavita (1,033) is about 2.69 times greater than that of the LED (384), and so is the photosynthetic output (umol/s) of the Gavita (1,751) at 2.68 times greater than the LED (653).

Therefore, that LED isn't more efficient than that HPS, and visa-versa, watt for watt they produce about the same photosynthetic output as umol/s. And that's the best-of-breed for HPS and LED at this time.

These data are for photosynthetic photons.

Beta Test Team · Nov 21, 2014

One more good graphic from that study because the issue of LED irradiance uniformity is a huge consideration that's often overlooked. And granted, the same is true of HID growers, but LEDs are even worse than most HID in good reflectors. The inverse square law is not nice to many LED arrays. However, again, these data don't include reflection from walls, floor, or ceiling, nor overlapping radiation from other light sources:

---------------------

"Figure 1: The photon distribution of four fixtures with similar photon efficiency.

Each line represents a cross section of the photon intensity below the fixture. The LED fixture (Lighting Sciences Group) uses optics to achieve a narrow distribution, with the majority of the photons falling in a concentrated pattern directly below the fixture. Conversely, the Cycloptics ceramic metal halide fixture is designed for even light distribution, and therefore casts uniform radiation over a large surface area. Since the area increases exponentially as the distance from the center increases, an equal photon flux farther from the center represents a larger quantity of total photons."

Duke Diamond · Nov 21, 2014

Ive been a user of leds for awhile in my house, I love the power savings.
What I would love to see is 3 clones, one flowered under led and one under hps and one under mh. Then testing yeilds, and flavors, and potency followed with a lab sheet on the buds.
Thats the only thing I could get as proof enough to use them.
Maybe one day when I have some spare loot i'll do a little small grow like that. Thanks for the info, good read :tiphat:

Beta Test Team · Nov 21, 2014

True, there are considerations that aren't taken into account by these data. One of which is cooling power needed (regarding radiant heat from HPS), which would increase the cost to produce each gram, all other things being equal. Another is the actual spectrum - if the photosynthetic photon output is converted into YPF (weighing each nm in terms of photosynthetic action), LEDs can have greater YPF per PPF than HID due to the ability to tune the spectrum.

LEDs have a few really useful and cool benefits as compared to HID. And same goes for HID as compared to LED. So I guess it's all in the application, use the best tool for that job

Duke Diamond · Nov 21, 2014

Absolutely , The rate the research and development is going now, I believe in the near future there will be something substantially better than what we have available now. It seems now everyones on the right path with the LED lighs and with research and tweaking, sky is the limit. Your right about the production cost as a whole to equal weight. Once the quality is there on the other side of the light, then its a wrap

Thanks to you folks putting in the work and research, it ends up helping our industry exponentially. The canna community to me is more impressive than all other industry I have been involved in, simply because the love and the heart is there...and stoners arent stupid like some folks are lead to believe

Thank you again :tiphat:

3dDream · Nov 22, 2014

Unless you change your hps bulbs every 3 grows led wins the long race. Do you want something to run down to 70% of it's brightness in 1 year or 5? I think this is a key issue: To be at peak levels with a HPS I would need to buy 5 bulbs to out-do one led. Forget about MH, those are worse.

Also, a DIY cree cob light can cost 1/2 of what is out there.

2 Legal Co · Nov 22, 2014

3dDream said:
Unless you change your hps bulbs every 3 grows led wins the long race. Do you want something to run down to 70% of it's brightness in 1 year or 5? I think this is a key issue: To be at peak levels with a HPS I would need to buy 5 bulbs to out-do one led. Forget about MH, those are worse.

Also, a DIY cree cob light can cost 1/2 of what is out there.

So where is the supply, design, etc for a DIY cob?

I'd be interested in seeing what Can be cone.

hazyfontazy · Nov 22, 2014

3dDream said:
Unless you change your hps bulbs every 3 grows led wins the long race. Do you want something to run down to 70% of it's brightness in 1 year or 5? I think this is a key issue: To be at peak levels with a HPS I would need to buy 5 bulbs to out-do one led. Forget about MH, those are worse.

Also, a DIY cree cob light can cost 1/2 of what is out there.

got any evidence to prove a hps is down to 70% after 3 grows or 1 year ?

most industry lighting is changing to led technologhy ,,i recently had a job changing all the streetlights in Birmingham uk to leds ,the efficency is amazing ,,lots of shops and factories also switching over ,,

the horti industry is lagging i feel

Beta Test Team · Nov 22, 2014

3dDream said:
Unless you change your hps bulbs every 3 grows led wins the long race. Do you want something to run down to 70% of it's brightness in 1 year or 5? I think this is a key issue: To be at peak levels with a HPS I would need to buy 5 bulbs to out-do one led. Forget about MH, those are worse.

Also, a DIY cree cob light can cost 1/2 of what is out there.

You're not taking all kinds of things into account, like the insane price for most LEDs and their lack of claimed efficiency in most cases (about ROI). See the first post, read at least the first two PDFs.

CMH have re-lamping time of around 10,000 hours when we want to keep radiation above around 90%, and high-end HPS have around 5,000 to 7,000 hours. LEDs also have life-spans, normally well above 20,000 hours, though.

It's like I wrote above, LED is a tool for a specific type of job. This isn't a LED is better than HPS thread, or a HPS is better than LED thread. They're both great for different reasons.

For example, LED are not well suited be used in a large warehouse setting for Cannabis, or even large room, to produce the same as HID (including HPS).

Well, let me back up, LED can be used in a warehouse, but it would: (a) cost so much you'd likely never get your money back vs. HID (see ROI); (b) it would make working in the facility inefficient, and; (c) you would likely get very low irradiance near the bottom of the plant relative to the top of the plant (so no trees, which is how most warehouse growers grow).

As I see it, the main problem with LEDs are:
1. Cost (see ROI)
2. Efficiency (see ROI and the info I wrote above, many are less efficient than HPS and even some MH and CMH)
3. Inverse-square law (physics) is not kind to most LEDs, which is why they must be kept close to plants for uniform canopy irradiation.

As I see it, the main problem with HPS are:
1. Spectrum
2. Useful life-span
3. Heat

LEDs are great, and will get better (and hopefully cheaper), but they're not a replacement for HID in many situations, and they are unlikely to ever be such, especially for Cannabis in large indoor growth areas.

Beta Test Team · Nov 22, 2014

2 Legal Co said:
3rdDream said:

Unless you change your hps bulbs every 3 grows led wins the long race. Do you want something to run down to 70% of it's brightness in 1 year or 5? I think this is a key issue: To be at peak levels with a HPS I would need to buy 5 bulbs to out-do one led. Forget about MH, those are worse.

Also, a DIY cree cob light can cost 1/2 of what is out there.

Click to expand...

So where is the supply, design, etc for a DIY cob?

I'd be interested in seeing what Can be cone.

Ditto, me too

I'm the first to admit I don't know much about future trends in LED technology. In fact we would like to carry out a few research projects using LED with Cannabis, so this topic is of interest.

Though can I request it be started as a new thread?

tenthirty · Nov 22, 2014

Really??

http://www.cree.com/~/media/Files/Cree/LED%20Components%20and%20Modules/XLamp/Data%20and%20Binning/ds%20CXA3070.pdf

and

http://www.cree.com/LED-Components-and-Modules/Products/XLamp/Arrays-NonDirectional/XLamp-CXA3070

and

and can be done for about $1.60 a watt or less and 30 watts a sq ft will do the trick quite nicely!

Beta Test Team · Nov 22, 2014

Not sure what you're responding to?

If to the LED array price points, those are for commercial units that most growers will use (most won't DIY), and in many cases growers legally can't DIY (building codes and whatnot).

Those photosynthetic umol/s values and photosynthetic umol/joule values are calculated from placing the whole light source (e.g. reflector + lamp, or LED array) into an integrating sphere.

How is PAR Watt defined and calculated in that spreadsheet image you posted? If by power it's not really PAR Watts, because PAR Watt is the energy emitted from the light source which can be converted into umol using Plank's constant.

Also, the issue of distance to canopy, its irradiance, and irradiance uniformity is important when considering the canopy area a LED array can irradiate effectively. LEDs are well suited for narrow benches and smaller areas, but not as well suited for large growth areas with large canopies.

tenthirty · Nov 22, 2014

Here is the Cree characterization tool.

http://pct.cree.com/dt/index.html

Beta Test Team · Nov 22, 2014

Thanks for that, interesting tool.

I don't see PAR W there, though. Only the human eye's use of photons (lumens). Maybe I'm missing something?

It would be very cool and useful if CREE would make that same type of tool for horticulture, and get rid of all the lumen data and lumen efficiency data, etc., using umols and other plant relevant radiation characteristics instead. Such a tool would be very useful indeed to CREE's customers.

luxcultivars · Nov 22, 2014

Duke Diamond said:
Ive been a user of leds for awhile in my house, I love the power savings.
What I would love to see is 3 clones, one flowered under led and one under hps and one under mh. Then testing yeilds, and flavors, and potency followed with a lab sheet on the buds.
Thats the only thing I could get as proof enough to use them.
Maybe one day when I have some spare loot i'll do a little small grow like that. Thanks for the info, good read

I'd like to see the same, but with 5+ plants in each of those 3 categories to get statistically conclusive numbers. Single-plant comparisons can be subject to inconsistencies.

luxcultivars · Nov 22, 2014

hazyfontazy said:
got any evidence to prove a hps is down to 70% after 3 grows or 1 year ?

most industry lighting is changing to led technologhy ,,i recently had a job changing all the streetlights in Birmingham uk to leds ,the efficency is amazing ,,lots of shops and factories also switching over ,,

the horti industry is lagging i feel

Yes. I've tested this repeatedly by measuring the lumens of my bulbs' output before and after changing bulbs. With an Eye-Horti bulb after 10 months of use the output has dropped to 70%. I've checked at least 3 times now.

Duke Diamond · Nov 22, 2014

that would be awsome lux. your right the more the more control for a good consistent average. :tiphat:

3dDream · Nov 23, 2014

You're not taking all kinds of things into account, like the insane price for most LEDs and their lack of claimed efficiency in most cases (about ROI).

This is why I built my own, but my needs are small. I know exactly how many lumens my led puts out because it was binned by cree, although I have to trust cree on that.

As far as the lumen drop: Google image search "Lumen Depreciation chart" or "lumen maintenance chart" - Ok, I overstated things a bit from memory. From what I see a hps vs led around one year of 12/12 would be at or below 85% and a led would be above 98%. I guess if you buy a better hps bulb you could be in the low 90's, but now you are into led pricing.

To each their own, I am done with the mercury and explosions.

So where is the supply, design, etc for a DIY cob?

Hi, all over the place? There are quite a few designs on this site and even more elsewhere. Google search cxa3070 and marijuana.

I made a small 40-100w dimable light with no moving parts with a big old heatsink, a cree cob, and a driver for around $150. I made a thread in the led section. I imagine a large heatsink (http://www.heatsinkusa.com/) with a dozen cobs would be easy to hang.

LED vs. HPS: Truth about photosynthetic eff. & uniformity

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