Fluorescent Lighting

[Dutch]

The brightest lights, i.e. highest lumen rating, are not always the best lighting for growing plants. The correct spectrum of light is more important.

The following picture is the light spectrum that most plants can absorb (use for photosynthesis). Please note that most plants are green and do not absorb (use for photosynthesis) much of the green spectrum.

Below is the light spectrum a typical plant can absorb (use for photosynthesis).
Plant Absorbsion Spectrum.jpg

Below is the light spectrum of a typical 4100K fluorescent bulb.
4100K Warmlight Bulb.jpg

Below is the light spectrum of a typical 6500K fluorescent bulb.
6500K Daylight Bulb.jpg

Below is the light spectrum of a typical 8000K fluorescent bulb.
8000K Bluelight Spectrum.jpg

This is why alternating every other bulb with an appropriate K (Kelvin) rating, can provide more light in the spectrum that plants can use for photosynthesis.
Dutch

P.S. You get more ultraviolet rays in 10 minutes outside in the sun than you get in an eight hour day in an office with 8000K lighting.

[Worth1]

It is in the right direction but there is a drawback to using human lights for plant lights.
Human lights are measured in lumens in the spectrum we see not the plant.

What we need to look for is spectrum and wattage, the lumens just happen to be along for the free ride for us to see as bright light.
So the higher the wattage the more lumens.

If you look at the graph for plants you see red and blue.
Red and blue make purple.
That is why grow LED lights put out that color.

And yes you can use wattage because it is a measurement of transfer of energy that just happens to be what the power company uses to charge you.
Light is energy and the watts can be used to measuer the amount of light for our use.

The electrical energy goes through the meter that measures watts, it comes out the bulb as light.

This is why like to put somewhere around 100 watts of light per square foot up close.
The higher the watts per square foot the farther away from the plant you can go.


I know there are more scientific ways of measuring light but the method I use works and isn't complicated.

This is also why the T 5 lights are better and why I use high wattage CFL lights in the 6500k range.
You can cram a lot close to each other.

The problem with the CFL and LED lights are the energy consumption is different than standard light bulbs.
For the home owner to get some sort of idea of what they need or want some companies put down the equivalent wattage for a standard bulb.

In other words 27 watts consumption equal to a standard 100 watt bulb.

But there is no standard across the board and they are for people vision so they put out lumens.


I just had this discussion with my boss.
He swapped out florescent lights in his kitchen for LED lights.
He said the place lit up like a UFO they were so bright.
That is when I told him about the kelvin rating and how we see it.
If person doesn't like the color of light these or florescent or LED's put out they are getting the wrong ones.

[Ricky Shaw]

Anything over 4000K is enough to get the life juices churning. Seedling's light demands aren't that high and the warmth is nearly as helpful in the early stages. An old style T12 shop light will put out nice 10-12" stocky plants, and maybe 13"-15" with T5's. At that point, plant demands are soaring and fluorescent's lack of penetration become apparent with spindly growth and less foliage. Which is perfectly fine, because it's time to go outside with them anyway. Just my experience.

[sjamesNorway]

What I believe is important here, is Photosynthetically Active Radiation or PAR. If you look at the attached "PAR influences" chart, you'll see that light in the range of 400 to 520 nanometers is "most significant in promoting vegetative growth". (Nanometers are a measure of the wavelength of color.) Vegetative growth is what is needed for seedlings. Looking at the PAR spectrum, you'll see that this range correlates closely to a color temperature of 6500K (Kelvin).

I use 58 Watt 6500K T8 fluorescent lights for my seedlings, and they do very well. 6500K fluorescent lights are commonly referred to as "daylight".

Light in the "warmer" (lower) Kelvin range promoting flowering and germination isn't needed until later, and is provided by the sun.

Remember that it's important to have the lights as close to the seedlings as possible without overheating them. About 2" is what I use.

[bower]

I find that purple plant light really hard on the eyes. Seriously I think I'm straining my eyes looking at plants under these lights, trying to make out if they are green or not. I find it so disturbing, I don't think I would ever buy it on the say-so that plants like it better. The plants have to accomodate me as well... I need to see them green or it's no fun.

I just picked up some new bulbs for the T8 fixture(s) - at least I have one fit to use, and the 6500 K was the better color and brightness IMO - also tried out a so called "Natural Daylight" 5000 K and the color IMO was very pink and pretty dim... I'm going to take those back.

Meanwhile I just got two new LED shop lights, delivered today and only half out of the box! Had to eat something before I get down to it. These are only 4000 K but they are 40 watts, 4000 lumens which is better than I can get in a T8. I have used "cool white" ie 4000 K in the past and I thought it was perfectly good for seedlings and/or greens.
This was a case of "price is right" in 4000 K only, not my first choice but I'm hoping to love these lights. As I do not love my fluorescents, no more.

[Cole_Robbie]

I agree with what Ricky said, that the light demands are so low for seedlings that the spectrum doesn't matter nearly as much as it does for large plants. High Pressure Sodium lights are about 2,200K, and I have used them with no ill effects. I had read before that the plants would be spindly under an HPS light, but that did not happen at all. AKMark has mentioned he uses HPS for seedlings as well.

I think of the spectrum of hps and metal halide lamps as being like a sawed-off shotgun, with the photons from the light being like the pellets from the gun. Most of them are going to miss the target, but that does not make the gun ineffective. All that matters is what strikes the target.

[Koala Doug]

I start all my seedlings now using T5 HO 6500k bulbs. They have noticeably shorter internodal lengths than when I used 'cool white' 4100k bulbs.

I also try to keep the tips of the plants about 1 to 1.5 inches from the bulbs.

[Dutch]

Steve (sjamesNorway) makes a good point stating, "light in the range of 400 nm to 520 nm is most significant in promoting vegetative growth". This is why the 6500K fluorescent bulbs are commonly used to start seedlings. Please note this is healthy growth, not over growth.
I use one 8000K bulb between each of my 6500K bulbs. I got a 12 count box of them on sale a while back and the mix of 6500K and 8000K appear to produce stronger seedlings then either the 6500K or the 8000K alone.
Dutch
P.S. Please note all my references to fluorescent bulbs have been related to 4 foot T8s.

[Worth1]

I have never seen an 8000K lamp.

Worth

[Dutch]

Originally Posted by Worth1

I have never seen an 8000K lamp.

Worth

Yo Worth, After the sun comes up this morning, I will take the 8000K box,
prop it up against my greenhouse and take a picture. Dig? Would that be cool?
Dutch

[Worth1]

Sure where did you get them?
Worth

[Dutch]

Originally Posted by Worth1

Sure where did you get them?
Worth

A Menard's store in Franklin, Wisconsin. The store was built on what use to be the pit area of the Hales Corners Speedway track. It was a clay (dolomite clay) track and hard as a rock. The parking lot was built where the track use to be.
Dutch

[Dutch]

Originally Posted by Worth1

Sure where did you get them?
Worth

Yo man, check it out.
8000K Skyblue Lamps.jpg
Gotta go now cause,
The sun's comin' up I got cakes on the griddle
Life ain't nothin' but a funny funny riddle
Thank God I'm a country boy!
Dutch

[Koala Doug]

Companies that sell saltwater aquarium lights will have all sorts of high degree Kelvin stuff: 10000k, 15000k, 20000k, etc.

I found that out a few years ago while researching better grow lights.

[Dutch]

Originally Posted by Koala Doug

Companies that sell saltwater aquarium lights will have all sorts of high degree Kelvin stuff: 10000k, 15000k, 20000k, etc.
I found that out a few years ago while researching better grow lights.

Yep, And I see quite a few cars with the higher ranger (blue) headlights at night.
The 8000K aren't too bad, but the ones that are over 10000K are rather annoying.
Dutch