Lights and You

Lots of people talk about light spectra and what to use here, but I hadn't seen any posts that really explained light beyond just saying what to use. So, I thought that I would expand on the topic a bit in a thread. It may not by sticky-worthy, but hopefully some people will find it useful, or at least interesting. So here goes...

Plants have two cycles that relate to light, the light cycle and the dark cycle, both of which are very important to their growth and development. The system is set up to work in conjunction with the sun, but since this section of the forum is dedicated to indoor growing, we can't really use the sun very well, now can we?

During the light cycle (which happens during most of the day while the sun is up), the plant's leaves absorb sunlight and then use that energy to produce sugars from carbon dioxide. The specific light that plants absorb to do this is blue light, which is one of the more energetic types of light in the visible light spectrum. So basically, the plant absorbs blue light during the day, and uses the energy from that light to produce its food (sugar) via photosynthesis. This is the light cycle. Daylight bulbs (rated at 6500K) will give off light in this blue part of the spectrum, and your plants will produce sugars well under them.

But when the sun starts to set, more of the red light that it gives off reaches us, which is why the sun appears red. Red light contains less energy than blue, but plants can still use it, and this is called the dark cycle. When the light that a plant recieves is mostly red, the plant uses the light energy to begin to metabolize the sugars that it produced during the light cycle. This is when your plant will do its actual growth, including height, leaf development, bud production, etc. Soft white bulbs (rated at 2700K) give off more red light than other types, and your plants will metabolize sugars and grow well under them.

Now, I can practically hear some people saying, "But BK, I've seen lots of grow journals of people on this site who just use daylight bulbs during veg, and their plants seem to grow just fine, even without bulbs in the red spectrum!"

And you're quite right about that; plenty of people do. But that's because lights that give off mostly blue light are still giving off light from the rest of the spectrum as well, including red. The plants are using that red light consume their sugars.

So what do we learn that's at all practical from this? Well, your plants can get the light they need from different kinds of bulbs, but the amount of needed light that they get varies quite a bit from bulb to bulb. To get your very best grow, you'll want more blue-spectrum lights than red, because then your plant will have more energy that it uses to produce sugars than it can use to consume them. But you still want to have red light present, because having plenty of red light means that your plant can eat all of that wonderful sugar it's producing under blue light, and so can grow big and healthy and beautiful.

So there you go, now you know why those mysterious numbers 6500K and 2700K are so important, and what they mean, and what they do. Hopefully people can use this information to enhance their grows, and help new growers to understand their light choices!

 

The type of light (tube vs. cfl) isn't so important, although with any fluoro light you'll need to have it very close to the plant, an inch or so. What matters is the spectra of the lights; as long as you have enough of the appropriate color of light, your plants will be fine. If you have to choose one color, I'd recommend blue over red. Once that's taken care of, more lumens is generally better.

 

As I stated in my initial post, you want a mix of red and blue light all the time, with slightly more blue if you can manage it. I'm not sure what you mean by tinted red lights though... if those are just bulbs that have a red coating, and so give off red-colored light, they will probably not work as well as soft white bulbs.

 

Those lights will work just fine, and I want to reiterate: Most lights will work, but lights that are closer to the generally recommended numbers (2700K for flowering, 6500K for veg), the more efficient your light output will be for plant growth. Different spectra ratings for bulbs aren't bad, they just aren't as ideal as those.

 

Wow, I can't believe I wrote that out so badly (sorry, I was really, really tired and had just gotten off 9 hours of work when I typed that up).

The dark reaction involves building up five carbon sugars from the light reactions to six carbon sugars, and the differences between the two types of light involve how the energy is used to produce sugars... I won't bore all of you with the details of the reactions, but light from both spectra is valuable to the plant at all stages of its life, because of the way that the plant uses that light to produce its sugar.

I meant for this thread to unveil a bit of the mystery between the two spectra of light that we use to grow, but I'm just now realizing that that'll be pretty much impossible to do without listing out all of the tedious information about chemicals and electron acceptors, etc...