Semi-tech --light spectrum for tomatoes

[loulac]

greyhost wrote :

I see the spectrum photos disappeared from the message

Hotwire was quite active in 2011, I saved quite a few of his posts at the time. You may mean that picture :

[artis]

Many of the things that Hotwire posted here in Tomatoville regarding grow lights were incorrect. His biggest mix-up was that he incorrectly assumed that PAR (Photosynthetically Active Radiation) and photoreceptor response was the same thing.

PAR only controls photosynthesis (conversion of light into chemical energy, for example formation of sugars from carbon dioxide and water). Photoreceptors are completely different and they control plant's response to light, such as short/long stems, movement towards light and flowering. Basically, PAR is like high energy food that goes into plant's "stomach" and photoreceptors are plant's "eyes".

https://en.wikipedia.org/wiki/Photos...tive_radiation
https://en.wikipedia.org/wiki/Photoreceptor_protein

In any case, Hotwire's claim that only 6500K fluorescent lights are good for plants in terms of PAR is incorrect. It may be true that bright 6500K light helps to grow short and stocky seedlings but that would be mainly due to photoreceptor response, not PAR.

By the way, here is a more realistic graph to describe photosynthesis efficiency for a typical plant such as tomato (from Wikipedia). Please note that red light is the most efficient for photosynthesis:

[RJGlew]

With all due respect, the best way to look at the light needs is based on the spectrum which chlorophyll A & B absorb. The graph I have included shows the absorption of both (the peaks), and you can see they both absorb light in the blue & red spectrum. In order to optimize the photosynthetic process, you must provide sufficient levels of light in those parts of the spectrum. Simply defining blue spectrum needs as `growing' and red spectrum needs as `flowering' is not aligned with this, although agreed that more red spectrum supports better flowering.

The best technology to provide the right blend of blue/red spectrum are the new LEDs since they combine both blue & red LEDs to provide the perfect light mix - a purple light. This has become a proper science within a certain home growing sector and I have provided a picture of a bulb which clearly shows the mix of blue & red LEDs which is optimized for growing their crop. These are expensive.

For starting tomatoes, fluorescent lights will work fine, and they are inexpensive. I have included 3 fluorescent spectrum for a) daylight, b) cool white & c) warm white bulbs. You can see that all of them provide some degree of blue & red light light. The specially designed fluorescent growlights provide more targeted blue & red spectrum for plants and are `better,' but much more expensive. I once built a graphic which shows all of the floresecent bulb sprecta perfectly aligned with the chlorophyll needs to show which is best, but it is too big to fit into the TV limits. PM me if you want a copy of it.

[artis]

Incidentally, Wien's law (that Hotwire misspelled) only applies to blackbody radiation. Therefore, it can only be applied to an incandescent bulb but it cannot be applied to a fluorescent light. Hotwire's correlations between the "temperature" of a fluorescent light and the wavelenght are incorrect.

https://en.wikipedia.org/wiki/Wien_approximation
https://en.wikipedia.org/wiki/Color_temperature

[loulac]

Thanks Artis, I stand corrected. Let me add that since 2011 some info by hotwire has become obsolete, no one uses incandescent lights anymore for seedlings. I'm not qualified enough to add information in that discussion, but I'd like to go further in the interpretation of the above piciture. Does photosynthesis measure the efficicinecy of lighting on seedlings or on mature plants ready to bloom and give fruit, or on both ?

[Worth1]

One of the problems with much of this information is all of the hoopla being sold and told over the internet.
You keep telling people a cow is purple and soon enough everyone believes it.
They are selling (GROW LIGHTS) that are way ever priced to people that dont know any better.
Then this whole red light (flowering) thing, lets face it for years they have been selling this idea to indoor pot growers.
If you look at my CD you will see that a bright daylight 6500K light put out a full spectrum this is what you want all the way from start to finish.
Or you can use red and blue spectrum LED's or 6500K bright daylight LED lights.
I have them and they also put out a full spectrum.

What triggers a "PLANT" to "FLOWER" is the amount of daylight and darkness it gets not dumping red light on it.
We all no what I mean by plant.
How do I know this, because I did it way way back in the 80's.
Another person on line growing tomatoes and such said there was no difference with blooming using CFL 6500K lights or 2700K lights.
If I had a choice of using one or the other HI light high pressure sodium or metal halide I would use the latter in the blue spectrum.
I have also had great results with the old 500 watt quarts iodine.

Worth

[Worth1]

Lets just say I have done some crazy stuff with plants and lights.

[RJGlew]

I re-sized the Stacked Spectra image to fit TV regs. Spectrum is aligned 300nm to 700nm & vertical lines included to make it easier to see chlorophyll peak needs.

[Cole_Robbie]

And there you have the reason why I can tell no difference between using cool white and day light bulbs. Whatever the difference is, it's not significant.

[Worth1]

Originally Posted by Cole_Robbie

And there you have the reason why I can tell no difference between using cool white and day light bulbs. Whatever the difference is, it's not significant.

Right.

Worth

[loulac]

RJGlew wrote :

The best technology to provide the right blend of blue/red spectrum are the new LEDs… These are expensive.

In years to come LEDs will certainly be used everywhere on seedlings (low wattage, little or no heat, regular intensity of light all over the seedlings, dosage of different colors etc) but the average gardener can’t afford yet adopting “space age technology” with LEDs lasting 20,000 hours. The market is flooded with inexpensive Chinese LEDs that were a disappointment for lots of French growers as they quickly gave less and less light. Before they discard fluorescent tubes or bulbs and buy LEDs growers will have to be very cautious.

[artis]

Originally Posted by loulac

Thanks Artis, I stand corrected. Let me add that since 2011 some info by hotwire has become obsolete, no one uses incandescent lights anymore for seedlings. I'm not qualified enough to add information in that discussion, but I'd like to go further in the interpretation of the above piciture. Does photosynthesis measure the efficicinecy of lighting on seedlings or on mature plants ready to bloom and give fruit, or on both ?

Loulac,

On a highly simplified level, photosynthesis is the conversion of visible light, carbon dioxide and water into sugar (plant energy). It should not depend significantly on the growth stage the plant as long as it is healthy.

Plant growth and flowering can be influenced by color and intensity of light and daylength but that would be due to mechanisms different from photosynthesis.

My apologies for the grumpy tone in the earlier message! Like Worth, I sometimes get annoyed by all the misinformation on the internet regarding grow lights. I suspect sellers of overpriced grow lights behind it.

Artis

[Worth1]

Originally Posted by loulac

RJGlew wrote :

In years to come LEDs will certainly be used everywhere on seedlings (low wattage, little or no heat, regular intensity of light all over the seedlings, dosage of different colors etc) but the average gardener can’t afford yet adopting “space age technology” with LEDs lasting 20,000 hours. The market is flooded with inexpensive Chinese LEDs that were a disappointment for lots of French growers as they quickly gave less and less light. Before they discard fluorescent tubes or bulbs and buy LEDs growers will have to be very cautious.

I'm going to put out about $24 for a 150 watt output 6500K one and put it in a chicken brooder fixture jut to see what happens.
It is a spot light I think.
I have a smaller version of it here and it puts out a full spectrum of light.
So what if it doesn't work I can use it outside but I bet it does.

Worth

[Worth1]

Originally Posted by loulac

RJGlew wrote :

In years to come LEDs will certainly be used everywhere on seedlings (low wattage, little or no heat, regular intensity of light all over the seedlings, dosage of different colors etc) but the average gardener can’t afford yet adopting “space age technology” with LEDs lasting 20,000 hours. The market is flooded with inexpensive Chinese LEDs that were a disappointment for lots of French growers as they quickly gave less and less light. Before they discard fluorescent tubes or bulbs and buy LEDs growers will have to be very cautious.

I'm going to put out about $24 for a 150 watt output 6500K LED and put it in a chicken brooder fixture jut to see what happens.
It is a spot light I think.
I have a smaller version of it here and it puts out a full spectrum of light.
So what if it doesn't work I can use it outside but I bet it does.

Worth

[Worth1]

Originally Posted by artis

Loulac,

On a highly simplified level, photosynthesis is the conversion of visible light, carbon dioxide and water into sugar (plant energy). It should not depend significantly on the growth stage the plant as long as it is healthy.

Plant growth and flowering can be influenced by color and intensity of light and daylength but that would be due to mechanisms different from photosynthesis.

My apologies for the grumpy tone in the earlier message! Like Worth, I sometimes get annoyed by all the misinformation on the internet regarding grow lights. I suspect sellers of overpriced grow lights behind it.

Artis

You are so correct and I hate to see people get ripped off.
I read all about this tom foolery back in the 80's.

Worth