Six weeks after transplanting the lettuce seedlings I am going to call the experiment done. The plants themselves are crowding their grow areas and I think they are mature enough to draw something like a conclusion. 53 days have passed between the time I planted the seeds (Jan. 14) and this final update, this variety is said to be mature is as little as 55 days from germination, I doubt a further 7 -10 days will make much difference.
The plant growing under the 9 “Grow” emitters was stunted in the first updates but has basically recovered by this point.
Picture 1 shows all six plants in their individual growing chambers and Picture 2 shows a detail view of the plants growth. The first four plants are notably taller than the final two but while it may not be clear from the photos, the final two are much denser and have a profile more like what is to be expected from this variety. Finally while none of the plants developed anything close to the depth of colour that this variety produces when grown under natural light the plant grown under the 6 Red and 3 Blue emitters had a noticeably deeper colour.
Additional Photos at the end.
Conclusions such as they may be..
First and foremost I find that I am quite disappointed by the results from the “grow” emitters, not least because I believed the manufacturers hype and had bought over a hundred of them for my next project. All four of the plants grown under the Grow and Cool White emitters are taller and more loosely grown than is typical for the variety, while I wouldn’t go so far as to call them “leggy” they are not the densely compact shape I would hope for or expect from these plants. (some of the plants required a coat hangar “prop” to hold them up in the photos) If I’m forced to choose I would say that the Cool White Emitters were marginally more effective than the Grow type. Both these types of emitter are “full spectrum”, they use a Blue or Deep Blue emitter to energize a phosphor like that found in a fluorescent light. It may be that there is energy lost in the process of energizing the phosphor or it may be that some of the energy is converted into wavelengths of light that are less useful to the plants. Whatever the reason for the difference the two lights built with the narrow band emitters produced better, or at least more typical plants.
There is one caveat I would like to make, both the grow emitters and the lights made from the narrow band emitters suffer from a similar problem, they give off a pinkish purple colour that is very hard on the eyes. This is not a big problem if you are using them in a closed environment like a grow tent but it is a problem if you are growing in a room that you may want to use for something else at the same time. A light built from a combination of the different white emitters could be used anywhere, while there would be a small sacrifice in energy efficiency I don’t know that it would be critical in most cases.
Ultimately however the best results came from the lights made with multiple narrow band emitters and of the two the one with the 2:1 Red:Blue ratio out performed the one with the 8:1 ratio.
The next big project is going to be a pair of 90 emitter lights, but the task is tedious enough that I wont be using the Grow emitters, so it will have to wait until I can get the emitters I want via ebay.