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Need advice for greenhouse supplemental lighting  RSS feed

 
Posts: 6
Location: Efland, North Carolina
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I am building a 20x8' greenhouse.
I'd like to get a light to supplement the sun on cloudy days.
What kind of inexpensive lights do people recommend?
 
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I'm curious what everyone says.  My plan when I build a greenhouse has been to use the LED grow lights that come on a strip about 16' long.  I've used fluorescent bulbs for seed starting and the power meter really spins when they're all on (8 fixtures).  But they work...
 
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Can you link to those LED lights? I've not found any LED's that use less W for a given area of use than florescent tubes do.
Personally I doubt it's worth running lights for cloudy days, it's still going to be pretty bright.
 
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I haven't done much research to say if these are particularly good lights, but this is one example of what I was thinking of.  I would attach one to each rafter in the greenhouse, which happen to be about 16' long.

LED Grow Light Strips
 
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Location: Pennsylvania, Dauphin County
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I really like the CMH, Cermaic Metal Halide lights.  Dimlux as an example.

they are closer to full spectrum and the bulbs last longer than HPS lighting.  I prefer these over LED lights as the LED lights will diminish and need to be replaced where you can change the bulb in the CMH light systems.

Heat dissipation is similar in CMH to LED.

The main problem I have with LED is the light footprint and penetration but their are models that do a better job of that but is still pricy.  CMH is not cheap either.

A traditional MH, Metal Halide light is an option to consider as well as well as potentially HPS lights but these put out more heat. 
 
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Location: Central Virginia USA
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I have not yet started to use them, so I speak only from research re: plant growing leds

site comparing cmh to LED

From this site it claims LEDS last longer and can be fine tuned as far as frequencies emitted, CMH have too much yellow and green, burn out much sooner and use probably two-four times more energy, plus they contain mercury.

another site opinion

    Ballast has 50,000-hour lifespan
    Recommended to change bulbs for veg and flower stages
    Higher PPF and canopy penetration
    Better standalone lights
    Offers full spectrum lighting in one bulb

LEDs

    Initial costs are steep
    Bulb lifespan is 50,000 hours
    Manufacturer guarantee of 5 years, Unit has 100,000-hour lifespan
    Numerous narrow bands of spectrum to create a full spectrum
    Dimmable
    Better supplemental lights


It's difficult to say reading between the lines, but I think the second site is less focused on conserving energy, and less conscious of mercury because at one point it suggests staying with flourescents. So it likely did not consider that in it's comparisons
 
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I have been pleased with LED strip fixtures.  I found some that are 4500 lumens per 2 bulb, 4-foot fixture.  Timer turns them on for a few hours at dawn and dusk.  Wow the plants have taken off under it.  Seems SO bright compared to my older fluorescents.
 
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Laura what distance do you have them from your plants?  Is there anyway you could post a pic or diagram?
 
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Jon Singinton wrote:
I'd like to get a light to supplement the sun on cloudy days.



Suppose the light intensity is 10,000 foot-candles when sunlit, and 1,000 ft-cd when overcast.
The photosynthesis rate when cloudy is not 10%, it's more like 50%.  Depending on what you're growing, light-saturation is reportedly around 2,000 ft-cd , as seen on a bright cloudy or partly-cloudy day. 

So there's a tendency for indirect sunlight to be undervalued.  It's worth noting that this indirect sunlight has more blue light (due to atmospheric scattering), having higher energy per photon and making it more valuable for photosynthesis.  So 1000 ft-cd of scattered light could be comparable to something like 1500 ft-cd of more yellow-ish direct sunlight. Indirect sunlight is more than half way to the saturation level.  The common use of opaque north-walls in greenhouses is mainly a strategy for saving heat, not for maximizing light use.  Indirect light is being sacrificed in order to reduce heat loss.  This is often a good design decision and trade-off to make, however it is probably one reason why reportedly a fully-glazed greenhouse can have twice the yield of a Chinese style greenhouse for example with only south glazing.  While it probably wouldn't be worth the trouble and expense, energy-wise it might technically be more efficient have a glazed north-side that was normally covered in thick opaque insulation but removed on warmer days, and particularly on warmer, cloudier days.

If you're on the electric grid, artificial lighting is probably more economically used well into the night.  As I recall plants might need some darkness but not much.  The slope of the photosynthesis curve is steeper at low light levels, so it's more efficient to provide a little extra light at night than a little extra on a cloudy day. 

A much more efficient and less expensive way to increase light levels on a cloudy day, especially for off-grid greenhouses, is to use reflecting concentrators; either white or silvered.  Although it's a design challenge to make them handle wind and snow loads outside, or to minimize floor space inside, and to minimize the labor of adjusting them.

Jon Singinton wrote:
What kind of inexpensive lights do people recommend?



In terms of minimizing both purchase cost and operating cost, I'll make two-categories for high and low light levels.  For lower light levels, I figure the standard white LEDs and florescents are high on the list. It's tough to beat their value.  Florescents are more efficient in the long tubes and with electronic ballasts.  They do contain something like a few milligrams of inorganic mercury vapor which may or may not concern you.  That is a difficult and controversial subject.  For the higher light levels, I read one cost-analysis paper claiming that high pressure sodium is the most economical, particularly with an electronic ballast.  Metal-halide is probably next. 

Another interesting lamp that is surprisingly overlooked is the neon lamp, and similar ones using neon-blended gases.  These are more-or-less as efficient as LEDs and florescents.  In some cases they can last even longer than LEDs. 

It seems unfortunate that the spectrum of these lamps isn't very well matched to the ideal photosynthesis spectrum, but the economics are such that it ends up getting very expensive very quickly to try to improve that.  Although some of the LED strip lights are suprisingly inexpensive, and basically one can just buy the color/wavelength they want.  Blue (400-500 nm) and red (625-675nm) are the most efficient for photosynthesis alone.  If maximum efficiency is needed, then those are probably the thing to use.  Although plants do use other wavelengths/colors too, and so other color/wavelengths can be useful and appropriate.  This is one explanation for why I think it's fairly reasonable to use inexpensive white lamps, which is good news for those of use without a lot of money, haha.

I've given some thought to ways that solar energy might be stored for later use as artificial lighting, but it's a difficult technical challenge.  I have some ideas that might work in the future, but for now it seems the most suitable available technologies are all well-known. 

 
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It depends on your PPFD & DLI targets. LED lighting tech is rapidly evolving but not yet at the point where it could compete in a greenhouse year round.

The problem is affordability and the less obvious factor that the amount of equipment even in the most efficient models available would be blocking the sun causing “shadows”.

The current best case scenario would be DE 1000w fixtures above with LED sub canopy lighting below for added light penetration.
 
Mike Jay
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Hi Elle, welcome to Permies!  What do PPFD and DLI stand for?  And what's a DE fixture?
 
Mike Jay
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I was trekking around the Amazon last night looking for light options for my greenhouse and I keep coming back to the LED strip lights.  My greenhouse has long curved trusses every 4'.  I'm nearing the electrical part of the project and I have to start thinking about lights and if I need them at all.  I'm in the cloudy northern midwest where, for instance, we have only seen a couple hours of sun in the last 10 days.

The greenhouse is very nice to be in on a cloudy day so there is a fair bit of sun getting in.  In January I'll probably only have 4 hours of direct sun and 4 hours of indirect, partially blocked light.  So...  Do I need some grow light help?  My plants will mainly be perennial tropicals with a smaller bed of annuals for winter eating.

The grow light fixtures I see advertised on greenhouse sites are enormous power draws and only cover small areas.  I don't want to put in dozens of fixtures sucking up 10,000 watts. 

LED strip lights sound neat because I could stick them to the underside of the trusses.  The light would come from the same direction as the sun (possibly not ideal for hitting hidden parts of the plants) and the LEDs would be invisible during the day and not block any sunlight.  The trusses are 1.5" wide so I could do three strips per truss if I wanted.  Most on Amazon are 12V with a transformer to plug into 120V power.  One commenter said that the transformer wastes 20% of the electricity.  There was one strip light that worked directly from 120V power Brilliant 148' strip light.  It's a huge roll but I have 9 trusses and the length would be about perfect for me.  Yay!

But...  The trusses start near the raised bed on the south side and rise up 16' in the air above the future bananas and avocados.  I think LEDs are recommended to be 12" or so away from the plants.  So would this even do any good?  Or is that close distance recommendation for optimal hydroponic lettuce yield and I'd still get a lot of benefit? 

Per Mike P's post above, extending the day with lights is more valuable than adding supplemental light during cloudy days.  So if that's true, I'd hope to still get some benefit.

Too long, didn't read: Should I bother with LED strip lights on the trusses high above tropical perennials or is it a waste of time/money?
 
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Location: Stroudsburg, PA (Zone 6a)
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If you place those strip lights too high, they will not do anything to help the plants. I have used inexpensive strip lights from Amazon (not exactly the ones in your link) in the past, and in my experience, they begin to dim after a while. I also had problems with them lasting much more than a year before I had transformer problems...although I don't believe the ones you have the link for have a transformer. I finally decided to invest in quality lights. They are not cheap, but you get what you pay for. They have done a superior job compared to strip lights I have tried in the past. I have a two fixtures from a company called Happy Leaf LED. They are the Procyon Ultra 33" - LED Grow Lights. I have 2 of them for my 2 3x6 raised beds in my greenhouse. They are easy to hang and adjust the level from a pipe. They do not quite cover the full 3 x 12 area, but I just slide them on the pipe every other day. They come with a 5 year guarantee. https://www.happyleafled.com/



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Procyon Ultra - LED Grow Lights
 
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