Why Red and Why Blue Light?

[CSF_Raziel]

I understand that blue(ish) light is more commonly used for vegging and red(ish) light is more commonly used for flowering, but why is that?

I know that blue light helps to keep compact nodes and that makes sense for veg. I also know that red light induces stretching (to some degree) so that makes sense for flowering.

However, why?

I can only guess...
That when the light is directly overhead (spring/summer in the northern hemisphere) that the light doesn't have to pass through as much atmosphere and therefore does not have as much red in it. If that's true, then when it is approaching fall/winter in the norhtern hemisphere, light approaches the earth at a more shallow angle and is more akin to the light you might see during a sunset (when the light passes through much more atmosphere and dust and giving it more ).

Does anyone have any articles talking about this? I haven't been able to find anything online.

Thanks!

 

[yesum]

I think you have it there. I just use white thru the whole grow. Works fine.

I think a bunch of red in flower will reduce quality, or in sativas at least. opinions vary of course.

 

[CSF_Raziel]

Well, I don't mean totally red or blue... I am referring more to the spectrum that Metal Halide and High Pressure Sodium bulbs emit.

However, I've definitely done grows with one spectrum all the way through and it was lovely.

 

[aridbud]

Colors above 5000K are known as cool colors (blue) and closely resemble natural sunlight. Colors below 3,000K are known an warm colors (red). The spectrum of light is important to horticulture because each spectrum triggers different responses from the plants—blue light induces vegetative growth, red light induces flowering. This in turn plays into which type of lighting rig you'll use and when—some types specialize in certain parts.

 

[CSF_Raziel]

Colors above 5000K are known as cool colors (blue) and closely resemble natural sunlight. Colors below 3,000K are known an warm colors (red). The spectrum of light is important to horticulture because each spectrum triggers different responses from the plants—blue light induces vegetative growth, red light induces flowering. This in turn plays into which type of lighting rig you'll use and when—some types specialize in certain parts.

Absolutely, I get that. But why? Does it have to do with the Earth's angle changing as the seasons change and the plant evolved to do certain things as that light changes?

 

[Coughie]

Absolutely, I get that. But why? Does it have to do with the Earth's angle changing as the seasons change and the plant evolved to do certain things as that light changes?

The red and blue is tied to the tilt of the Earth's axis in relation to the sun... You've got that part figured out.

The plants flower based on the light-hours, not the color of the light, which is why people will flower 16-22 week sativas using blue MH and it works just fine..

The amount of red you see in the atmosphere / light spectrum depends on your latitude, and the farther from the equator that you are, the larger the kelvin color changes..

Equatorial sativas do better under that blue MH when flowering because the blue-to-red-to-blue-to-red change seasonally at the equator is far-less than the effect seen in say.. Alaska or South Africa..

It's always pretty "blue" on the equator, while its blue in the spring and red in the summer for those 40N & 40S of the equator, for example


They are related, the two thoughts, but the plants didnt evolve to the color of the light so much as they evolved to the hours of light / amount of light, when it comes to "when to flower"

 

[Lyfespan]

MIT physicists explains why the sky is blue, red or white @ 34min on

[YOUTUBEIF]https://www.youtube.com/watch?v=4a0FbQdH3dY[/YOUTUBEIF]

 

[corky1968]

My last grow was with Sativas and I used T-12's to start with. I then added
a quad T-5 fixture which has a pair of 6,500K bulbs and a pair of 10,000K bulbs.

Initially, I had a pair of Actinic bulbs which is insanely in the blue spectrum before I got the 10,000K bulbs.

In flowering, I switched to a 600w MH with a 7,200K bulb.

This time around I'm doing the same seeing how well it all went.

I'm forever sticking with the blue spectrum.

 

[MJPassion]

Search "phytochrome"

I like the way plants flower under MH better than HPS.
I think MH produces denser plants with a slightly higher trichrome density over HPS.
I can't prove it though.

Red light right before lights off helps to build up the phytochrome levels in the plant.
Once the plant has enough phytochrome built up, it begins flowering.
Plants grown under MH typically take a few days more to finish when compared to HPS.

 

[Pinball Wizard]

I think MH (4000K) is good ...start to finish.