0:00 Hi, I'm El Gracion from elbow pepper.com. Do you like experiments, hydroponics, grow lights? Well, perhaps you're familiar with this popular generalization. Blue light is for veg and red light is for fruing or for blooms. Well, what exactly does that mean? Can plants grow under red light even when they're not fruing? And what would a plant grown under pure red light look like? For that matter, what about one grown under pure blue light? Well, my inquisitive YouTubers, today we're going to find out. We'll compare some lettuce plants grown under three
0:46 different color combinations of LEDs. And we'll even throw in a full spectrum CFL to see how that measures up. In today's experiment, we'll test the following hypothesis. Blue light fuels vegetative growth. Thus, lettuce plants grown in the absence of blue light will grow slowly and develop less plant mass than lettuce grown under blue light. Let's look at the lights we're using for our control. We have a 26W 6500 K spiral CFL with a reflector. Our blue light is an ABI LED PAR 38, 460 nanometer. I have a multicolor HE that uses three colors, 460,
1:35 630, and 660 nm. And our red is an ABI 630 nmter. Here are their stats along with their actual power draw. I crafted a super compact chamber for each plant designed to separate and isolate them. The lights will be placed 10 and 1/4 in above the tops of the containers. I'm growing one lettuce per light. The plants are pre-erminated and selected for matching vigor and grown in identical passive hydroponic solutions. This technique is coined crack keys method of hydroponics. And here's the setup. Each plant has a 2 L amount of
2:22 solution. So I won't have to worry about things running out. And here we are out of the gate with our little seedlings ready to grow. After 9 days, the plants are underway. Each one is doing well and they all look a little bit different. Another week goes by and look at the CFL growth now. The plant's looking pretty good. What about the blue? A little bit more of an upright structure. And uh what about the red blue? Look at that. A shorter plant with wider leaves. Hm. How about that red? Whoa, that's some elongated leaf growth. How about another week ahead? Oh man, the CFL it's looking pretty good so far. little bit
3:09 of some outer leaf tip burn, but uh otherwise plant looks healthy. As for this blue light, if it's having any issues, you really can't tell because of the color of the light, but look at how it's just really filling in this area. The leaves are stretching, but they're thick. On the other hand, here we're seeing a plant with wide leaves, but a shorter, bushier structure. And what about the red? Ah, this stuff's going crazy. Look how elongated these leaves are. This is nuts. Space is running out. So, I imagine that in another week I might have to wrap things up. Whoa. This experiment is out of control.
3:59 Just two days ago, this plant was looking great, but look at it now. So much for having enough solution. It would seem that the extra heat from this CFL boosted transpiration rates looks like I have to cut this test short. Reduced heat generation is a huge benefit of using LEDs. So, here we are now, guys. The results are in and every single one of these plants looks very different for probably a few different reasons. Let's take a closer look at each of these plants to really see how the quality of light and the general setup of this experiment impacted their
4:44 development. This lettuce is toast, but the general development of the plant had looked pretty good. Full spectrum light yields nice growth. It allows you to monitor your plant easily identifying physiological issues. Now, let's look at our pure blue lettuce. We have a very upright structure with a nice deep green color. There are some signs of disease and some tip burn. At the top, we see some deformity and leaf growth. Root growth looks good and this plant seems to have more mass than our next one. Here we have our combination red blue lettuce. This thing had very compact
5:30 growth, very tight, but also deformed, serious inner tip burn. When I see this, I suspect that the light source was too intense, perhaps too close. But now, look at these roots. Much more root development than our blue plant. Finally, there is our pure red lettuce. Did it grow more slowly? No. Was there less plant mass? Possibly not. We need to weigh this. But look at the flimsy weak structure. There is so much elongation. It resembles a lettuce plant that is starting to bolt. And of
6:15 course, the color. So pal looking. And look at this yellowing on these upper leaves. This is leaf bleaching. It was so close to the light that the tissues were damaged. What about the roots? Hm. Nice strong root growth, better than the blue light. This is a huge bummer that I can't gather data about the CFL plant, but I can at least get my fresh weights from the LED plants and I can analyze the remaining solution. Wait, what about the dry weight? I don't really want to eat these, so I think I'll dry them. All right, I've collected all of my data. And here's a complete chart of
7:02 everything. Remember our hypothesis? It would appear that we've disproved it. The plant grown under the red light produced 34% more upper fresh mass. The total dry mass, including roots, was much closer, basically the same. Interestingly, this was achieved using 29% less power. In each of these plants, we saw mechanisms beyond basic photosynthesis. Are you familiar with the photosynthetic absorption spectrum? This shows the wavelengths of light that chlorophyll pigments absorb. PAR spans from 400 nmters to 700 nmters,
7:47 including the colors in between, even green light. All of these frequencies of light drive photosynthesis with various degrees of efficiency. But what explains the different growth characteristics we saw, especially with that red light? The answer lies in photoorphogenesis. Photomorphagenesis deals with the effects that different wavelengths of light have on plant development. Certain colors or combinations of colors can yield very different responses from a plant and the responses can vary greatly depending upon the type of plant. Now, red light is capable of driving plant growth, but
8:37 unless it's accompanied by blue light, the plant may develop elongated growth. The lettuce appeared as if it was entering its reproductive phase, that flowering and fruing. That's not something you want with vegetative leafy crops. Also, it was very pale and appeared to have reduced chlorophyll concentration. It did show greater root mass than the lettuce grown under pure blue light. Both red and blue light can trigger abnormal morphologies if they're not mixed with additional light wavelengths. Identifying that perfect ratio is something that can change with plant type and even with light intensity. New
9:24 research is always coming out. Incidentally, what else did we observe in this test? Well, some things that can help all of us in our indoor gardening. CFLs can help with growing plants, especially by rounding out the light spectrum, but they're less efficient than LEDs, and that means more wasted heat. Lack of air circulation can cause problems for plants, especially hydroponics. But in particular, excess light can cause serious problems. We saw leaf tip burn. The lettuce grown under the red LED had damaged plant tissues. And what about the inhibited growth? Some leaves
10:10 appeared stunted. Such growth can be a sign of photo inhibition. Photo inhibition occurs when excess light actually reduces the photosynthetic capacity of a plant. With lettuce, for example, researchers have identified certain light saturation points. Once the PPFD levels get to that point, there is little additional growth. Selecting the appropriate lights and using them in the right way is crucial to avoiding photo inhibition. We need light to emit enough photons over as much of the canopy as possible. But
10:56 once we hit those optimal PAR levels, any further light is simply a waste of energy and may even damage the plants as we saw. That's why quantum light sensors are essential tools for professional growers. Running this test caused me to bite the bullet and get a high quality PAR meter that also works well for LEDs. This Apogee SQ 520 fits the bill and it can plug right into a PC which makes it super high tech. Here are the PAR readings at three different distances from each light source.
11:42 So, we can see that these LEDs were far too close from the start. And that problem was only compounded as the plants grew. I hope this test and its results have offered you some useful information. When people talk about red and blue light, we can see that there's a lot going on and there's still more to learn. Thanks so much for your support on my channel. Thanks for watching this video and for liking it and for sharing it with all your friends and for following me on Instagram and liking my Facebook page. You guys are the best. That's all for now and as always, happy gardening.
