September meeting: LED lights

As promised the September meeting was a techie dream come true!  We were able to check out the photosynthetically active radiation (or PAR – the component of light that plants can actually use for photosynthesis) as well as the spectra produced on not one but four different LED grow-light fixtures!  Don’t worry if you are not as techie though.  Not all of our meeting are this technical.  Mostly we talk about growing carnivorous plants, so if this level of detail is not your thing, don’t let it stop you from attending out next meeting in November.  Details to come.  Any questions, as always please feel free to contact us at our e-mail address, username: umcps

On to the details!  For those unfamiliar with what most of these LED fixtures look like, here is a picture:

LED grow fixture

You may, very reasonably, be asking yourself why you would want to use a light fixture with that sort of color to it.  It certainly doesn’t make the plants look very nice.  These bulbs are not lights for admiring your plants under.  Nope.  They are meant to make them grow while using as little energy as possible.  They are “tuned” to your plants not your eyes.

Let’s explain what that means.  Our eyes make use of a very different part of the light spectrum than plants leaves do for photosynthesis.  While we are very tuned into yellow and green (baring types of color blindness), plants don’t use green very well – which is why they look green to us.  Plants use reds and blues best.  Below is a spectrum image of the wavelengths of light plants use, which we have borrowed from here (which is a really great site talking about photosynthesis in general!):

Photosynthetic Pigments

You can see that light in the green bands, around 550 on the bottom axis are used pretty poorly.  Whereas, the blues at about 420, and the reds, about 650 are what plants absorb best.  So if you wanted to target the lights to use as little energy as possible while getting plants to absorb as much as possible, you would want to use red and blue lights.  See where that magenta color is coming from now?  That’s the idea behind the production of LED grow lights.  They are tuned to me as useful to plants as possible.

Now we know what light plants use and the type of absorbency they are trying to produce.  So how did the four LED fixtures do?  Here is the spectra from the first one.  It is a generation 1 (or Gen 1) fixture, and early type that only used 3 bulb types.  Blue, red, and orange.

Gen 1 LED spectra

You can see that it really just has peaks on the red and blue with a little orange near 625.  So that’s pretty good right?  Well it turns out plants get information and collect light from the other parts of the spectrum as well, and so it helps to have a little light in those regions as well.  The next spectrum is from a Gen 2 fixture, that includes a white LED as well.  This fills in some more of the spectra as you can see.  Oh and don’t worry about the intensity on the vertical axis – we had to adjust them at different distances to get the highest peak to fit on the graph, so these graphs are of relative intensity between fixtures.

Gen 2 LED spectra

On the Gen 2 graph above you can see that the addition of the white LED bulbs fills in that saddle between the red and blue parts of the spectra better.  But it still doesn’t replicate the curve of the light that plants absorb quite correctly.  And that why people developed Gen 3 fixtures, of which we tested two.  This first spectrum is from the first one we tested, which we’ll arbitrarily call “type 1”.  This one includes 9 types of LED bulbs covering a range of the spectrum, including one infrared (IR) bulb type.

Gen 3 type 1 LED spectra

You can see the IR bulb’s influence as the small bump to the right of the red peak.  The shape is a rather impressive approximation of the absorbency curve for photosynthesis.  The last spectra is from the other Gen 3 fixture, here called “type 2” because we tested it second.  It also has 9 types of LED bulbs.  This is the curve from that fixture.

Gen 3 type 2 LED spectra

Interestingly this one is a little peakier, if that can be a word.  And the general consensus was that it didn’t match the optimal as well as the type 1 fixture did.  Despite it supposedly having IR bulbs too, we didn’t really see a signal for those.  Unfortunately because the fixtures are individually made and purchased on e-Bay there is not a lot of assurance about which exact spectrum you might get.  Once these sorts of fixtures become more common and produced on a larger scale, there might be more standardization.

The last thing, and if you’ve read this far you can consider yourself very techie, is the PAR readings.

in (µmol m-2 s-1)       @12 in                                   @24 in

Gen 1                          354                                            92

Gen 2                          250                                            74

Gen 3, Type 1             260                                            65

Gen 3, Type 2             178                                            51

Given how bight these bulbs were to the eye the PAR readings seemed at first very low, with numbers no too different from T5 or T8 fluorescent fixtures.  But those fluorescent bulbs throw off a lot of light plant’s aren’t using.  Those of you paying close attention may object to that last sentence.  PAR is supposed to measure the photosynthetically available light!  So how can the same PAR mean different efficiency coming from different fixtures?

It’s a good question and the answer is in the details of how PAR is measured.  The short answer is that PAR weights all wavelengths of light equally between 400 and 700 nanometers.  But as we can see from the photosynthesis absorbency graph earlier that’s not how plants work.  So why was PAR designed that way?  PAR was meant to measure light from black body radiation, things like sunlight and light from incandescent bulbs.  For those things it is very good metric.  For LED bulbs that produce a very narrow band of light, it becomes more problematic.  This means that with the same PAR reading a well tuned LED might allow a plant to photosynthesize at a higher rate than a fluorescent bulb with the same PAR reading.  So, it becomes difficult to compare directly.  Someone is going to have to come up with a new metric if we all move to LED fixtures.

That’s it!  Hope it was interesting for those who read this far.  Please feel free to leave comments if you have any thoughts on this topic.

Meeting Date Change & State Fair Picts

There has been a last minute change to the meeting.  It is not tomorrow, Sept. 8th, as originally scheduled.  The meeting has been postponed for one week and will now be on Sunday, Sept, 15th at 4pm at Sunrise River Farm.  We are very sorry for the last minute notice, but it is going to be worth the wait.  One of our members will be bringing new LED grow light tubes and talking about where this technology is headed.  We will also be testing the LED bulbs against more typical fluorescent tube bulbs for the plant usable light (photosynthetically active radiation – PAR) as well as quantifying the difference in the spectra produced by the two bulbs.  It’s a techie’s dream meeting!  So, if you are into plants and electronics this is a must attend meeting.

The other reason we have decided to delay the meeting is to give the hardworking members who worked our booth at the Minnesota State Fair a chance to catch their breath.  Our dedicated members setup a great table to display the wonders of plants that consume kill animals for nutrition.  We didn’t win anything big, but it was a great display, and they did an incredible job, as some of you who chatted with them there recall.  They made some new friends, and had a great time too.  We could go on about how great it all was, but perhaps it’s better to let the photos speak for themselves.

CP at MN State Fair native CP of MN State Fair Bladderworts State Fair Dews State Fair Pings State Fair Pitcher State Fair VFTThere was a little of everything.  If you want to hear a recap of the events from the Fair come join us next Sunday.  If you have any questions of need directions please contact us at our e-mail address, username: umcps.  Hope to see you next week!

We’re on Facebook now too!

For those of you facebookians out there who were hoping for a more interactive forum to talk about carnivorous plants in the upper Midwest, we now have a page on The Facebooks.  On the face of it, it seemed like a good idea but it will only succeed if we get people interacting face to face.  So if you are a facebooker and want to get some face time with each other to discuss the face of carnivorous plants head over to our Facebook page.   Facebook!

Enough of that silly writing.  Our next scheduled meeting is July 14th, but we are hoping to schedule an extra meeting in June.  One of our members has kindly agreed to share his experiences with LED lighting on his carnivorous plants.  There has been a lot of talk about LED lighting as the future of indoor pant growing and plenty of disparaging comments against it as well.  We are hoping to have the meeting so people can see for themselves.  Another of our members is planning to bring some equipment to quantitatively assess the LED lighting.  It will be a great opportunity to see LED lighting and form your opinion.  LED lighting: the future of indoor plant growing, or a technological dead end.

Stay tuned for the meeting details, time and place, etc.  And if you have questions, the best way to get an answer is to e-mail us at our address, username umcps