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[ARTICLE] Light 101


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#1 Omri

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Posted 29 October 2011 - 04:12 AM

Hey everyone,
As some of you remember, I used to run a website about chiles and the technology used to grow them. well it doesn't exist anymore and thought it would be wise to post some of the information I published there. today I'll post a brief article about light, plants and their relationship. please bear in mind the article was written a couple of years ago and some data might be outdated. will do my best to fix any such data. enjoy. :)


Part I: The Basics

Light & Plants

Light is one of the most basic requirements for the existence of plants. the energy source of plants is sugar. instead of consuming it like almost any other life form, plants create their food in a process called Photosynthesis. for this process to occur, the plants need water, carbon dioxide (CO2) and sunlight which is the source of energy stored in the sugar.

The Different Colors

The white light is composed of many different colors, just like demonstrated in a rainbow. different colors of sunlight can be seen in different parts of the world and even different times of day. plants react differently to various colors of light, and will actually use only some of them in Photosynthesis. the two main colors of light used by plants are red and blue. high concentrations of red light are manifested in yellow - orange light and blue in white - bright-blue light.

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The color of light is labeled as color temperature. The color temperature of a light source is determined by comparing its chromaticity with a theoretical, heated black-body radiator. The temperature (in Kelvin) at which the heated black-body radiator matches the color of the light, is that color's temperature.


Part II: Hardcore Data

Photosynthetic Activity

The light receiving photosynthetic pigments of the plant are located in the thylakoid membrane of the chloroplasts. the most common pigment in its quantity and is present in all green plants and algae is ‘Chlorophyll a’. other pigments are called secondary pigments and include ‘Chlorophyll b’ and carotenoids. to every photosynthetic pigment there is a typical absorption spectrum, meaning a different absorption ability of light in different wavelengths.

  • Chlorophyll a – 420nm, 663nm
  • Chlorophyll b – 453nm, 645nm
  • Carotenoids – 420nm-480nm
The light receiving pigments' array, constructs a type of antenna that is used to transfer light energy to the reaction center (Chlorophyll a), which drives the process in Photosynthesis. the quantitative ratio of different chlorophylls varies in different plants, parts of the plant, different exterior conditions and different times of year.

Posted ImagePosted Image


The absorption by the Chlorophylls is mainly obvious in the red and blue-violet area, although absorption lines in other areas do exist. Chlorophylls a and b are distinguished by the wavelength at which maximum absorption occurs. the absorption lines of Chlorophyll a at both the blue and red ends of the spectrum are farther away than the absorption lines of Chlorophyll b. Chlorophyll quantities in a green leaf vary between 0.05%-0.2% of the fresh weight. the ratio between Chlorophyll a and Chlorophyll b is 2.5/1=a/b, although it is not constant due to the fact Chlorophyll a is more easily destroyed, meaning the quantitative ratio varies under different conditions.

Types of Plants

Sun and shade plants differ by various leaf qualities due to the amounts of light reaching them. shade plants allocate more resources to harvest light than CO2 fixation. This is why in shade plants the secondary pigments are produced in greater quantities – more Chlorophyll and less RuBisCO*.

* Ribulose-1,5-bisphosphate carboxylase (RuBisCO), is an enzyme that is used in the Calvin cycle to catalyze the first major step of carbon fixation, a process by which the atoms of atmospheric carbon dioxide are made available to organisms in the form of energy-rich molecules such as sucrose.


Part III: Artificial Light

Whether you grow indoors or simply need an additional light source, artificial lighting is a popular and relatively easy solution these days. today we are going to discuss some of the more popular solutions in artificial lighting, but first we will answer the question: “What makes a good light source?”

As you can read in Part I and Part II, plants use certain colors to convert the energy of light into a usable energy source (sugar). so the first thing a good light source should have is the main colors being used. obviously the perfect light source will have them all. another important quality a good light source should possess is high luminous intensity*, thus the amount of energy reaching the plant and eventually being converted is high. the last thing we need to remember when choosing a light source is cost. usually artificial lighting means the use of electricity as an energy source, as with standard light bulbs. electricity costs money, so a good light source will supply the right colors, will have high luminous intensity and of course will do all of that with as little electricity as possible. with the sun having all possible colors used by plants, extremely high luminous intensity, it’s no doubt the perfect light source and it can’t get any cheaper than free. it is perfect, but when that fails we need alternatives.

Incandescent Lamps

Incandescent lamps work on the Incandescence** principle and are possibly the most common type of light source used in private homes. contrary to what you might think, incandescent lamps are not a good light source. they only contain some of the colors needed by plants, mostly from the red end of the spectrum and the Lumen/Wattage efficiency is relatively low. meaning low luminous intensity and high cost.

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Fluorescent Lamps

Fluorescent lamps are a type of gas-discharge lamps and also a common light source. With a wider spectrum and much more flexibility in producing certain wavelengths, the fluorescent lamps are a much better light source than incandescent ones. the relatively high Lumen/Wattage efficiency will help keep the costs low with only few actual shortcomings. the first one being the still not high enough luminous intensity, meaning the lamp should be kept as close as possible to the plant. this might not be a real disadvantage with seedlings, but the cost is quite high with most mature plants. another one is the requirement of ballasts, which limits the possible lamp designs. compact versions (CFLs) with ballast built-in are sold, so one could just use a standard lamp holder, but the cost of those lamps is usually higher.

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High Intensity Discharge Lamps

High intensity discharge (HID) lamps are arc based. The actual conductor varies depending on the color temperature and luminous intensity sought for. HID lamps are quite popular in the industrial sector, especially as an alternative light source for plants. with one of the highest Lumen/Wattage efficiency out there, they’re probably the best artificial light you can find. the most notable HID lamps in agriculture are probably Metal Halide (MH) and High Pressure Sodium (HPS), with the MH leaning toward the blue end of the spectrum and HPS to the red one. like the fluorescent lamps, they also require ballasts. some even require special conditions for them to operate. indeed, HIDs need much care in terms of investment, but they’re worth it.

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Light Emitting Diodes

Light Emitting Diodes (LED) are semiconductor based solid state diodes. they are very common in electronics and as indicator lights. The current Lumen/Wattage efficiency is not enough to compete with some of the other solutions, but this recently hyped light source has its advantages. a possibility to replicate the wavelengths plants need is one of them. With the right components, it is possible to create an array with most possibly the best artificial spectrum. Another advantage is the lack of moving parts, something that influences the life span and usage for the better. the technology is still underdeveloped, but future developments should improve overall efficiency. for now it is not your best choice, even though it is a good one.

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* Luminous intensity is a measure of the wavelength-weighted power emitted by a light source in a particular direction, based on the luminosity function, a standardized model of the sensitivity of the human eye. the SI*** unit of luminous intensity is the candela (cd), an SI base unit.

** Incandescence is the release of electromagnetic radiation, usually visible radiation, from a body due to its temperature.

*** International System of Units


I hope this helps. :)
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#2 SuperHot

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Posted 29 October 2011 - 09:20 AM

I guess if you're doing the whole grow inside a combination of the (MH) and (HPS) would cover the desired light spectrum better than just one while producing the most lumens of the group. Looks like there is no one magic bullet, at least not yet.


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#3 Shadowchilli

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Posted 29 October 2011 - 11:39 AM

Just wish this was around a few months ago, lol.
Taking a lot of good info from this :)
Thanks Omri.

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#4 MGOLD86

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Posted 03 November 2011 - 08:13 AM

Great Info Omri. Definitly learned a few things.

Stop asking and just eat it!


#5 willard3

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Posted 03 November 2011 - 09:09 AM

You should sticky this at the top of Grow Tech, Omri; it is good basic scientific information.

It may lessen the constant questions about lighting and the constant opinions about the subject.

Lighting is really quite simple, scientific and predictable.
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#6 Omri

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Posted 03 November 2011 - 09:21 AM

Thank you everyone.

I might just will, Willard. :)
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#7 talas

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Posted 06 November 2011 - 01:57 PM

Great Info from a man who knows his end of the Light Spectrum..wish i had this guide years ago. :cool:
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#8 LoveTheBurn

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Posted 30 November 2011 - 03:41 PM

Fantastic article!! Thanks for sharing.

#9 busamadman

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Posted 22 December 2011 - 06:47 PM

I guess if you're doing the whole grow inside a combination of the (MH) and (HPS) would cover the desired light spectrum better than just one while producing the most lumens of the group. Looks like there is no one magic bullet, at least not yet.


There actually is a magic bullet, we just can't buy it. The Sulfur Bulb. Developed by a small company in Rockville, MD, it uses a magnetron (like a microwave emitter in your kitchen, not a Hasbro Transformer) that hits a sealed sphere filled with sulfur vapor under a vacuum. There is no socket and the 'bulb' is about the size of a golf ball. To keep it cool, since it is a 5,000 Watt bulb, it sits spinning on a stream of compressed air. (Neat-O!) Later ones used a glass rod attached to the bulb that spins which was less trouble-prone. The big point on these bulbs is that they are VERY close in spectrum to our Sun around 10-11 am in the morning.

The Air & Space museum in DC used two of these to power a light pipe that illuminated their huge front room. I don't know why these disappeared from the marketplace. They are probably not cheap, but (1) 5,000 W sulfur bulb does the work of about (20) 1,000 W HPS lamps.

Here's more on the sulfur bulb:

http://www.kbmorgan....hbull/bull6.htm

Genius DIY'er:
http://www.youtube.com/watch?v=okku7DiS9p4&feature=related

#10 mygrassisblue

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Posted 25 December 2011 - 09:33 AM

Omri great info thanks ! (Thanks Busamadman !!! The article concludes that the bulb may available commercially in two years.)

#11 HillBilly Jeff

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Posted 08 January 2012 - 04:32 PM

Great read thanks!!!

You do your thing, I'll do mine.


#12 Beehunter

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Posted 10 January 2012 - 07:12 AM

This is my first year starting seeds in winter and my this article has been a great help!!! Thank you very much for this posting!

#13 judohero

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Posted 15 January 2012 - 12:42 AM

after reading this i might have changed my mind again. would this be a good choice. http://www.ebay.com/...=item68c836719c.

or this one

http://www.hayneedle...tubefixture.cfm

i do plan on puting the peppers in my sun room when it gets warm enough.

Edited by judohero, 15 January 2012 - 12:53 AM.


#14 neobepmat

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Posted 12 February 2012 - 05:41 PM

Nice job Omri ;)
I've already bought the lights for my new Lightbox and I spent many nights to search detailed information about the optimal lighting to adopt, if I had found your page a long time ago for sure I would have saved lot of hours reading and surfing the whole web!
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#15 Blinky

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Posted 16 February 2012 - 04:30 PM

So how close would a florescent light need to be to seedlings?

#16 neobepmat

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Posted 17 February 2012 - 05:24 AM

So how close would a florescent light need to be to seedlings?

It depends on how many watts the CFL provides.
Based upon my experience, with 40W CFL the minimum distance might be 4 inches (8-10 cm.).
Stronger lights might require at least 6 inches (15 cm.)
Best practice is to set up a distance and after 2-3 days have a check on the seedlings to detect the presence of dark spots on them.
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#17 Nagel

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Posted 24 February 2012 - 04:24 PM

Interesting read... Have you ever researched the dual ballast HID bulbs? i.e. the Iwasaki HPS bulb? I came over from the reef tank side, and lots of guys used the iwasaki bulbs with MH ballasts (cheaper bulb than a 10k or 14k bulb). They run at 6500k typically, but are cheaper than MH bulbs, have AWESOME par levels (corals are photosynthetic too!), and since I've done my reading and it seems like many people veg under MH and switch to HPS for flower / fruit (or is it the reverse?), this bulb might be a good option for some since you wouldn't need to have an HPS ballast and a MH ballast..

Just thinkin' out loud...

#18 Capsicum

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Posted 02 March 2012 - 02:05 AM

There actually is a magic bullet, we just can't buy it. The Sulfur Bulb. Developed by a small company in Rockville, MD, it uses a magnetron (like a microwave emitter in your kitchen, not a Hasbro Transformer) that hits a sealed sphere filled with sulfur vapor under a vacuum. There is no socket and the 'bulb' is about the size of a golf ball. To keep it cool, since it is a 5,000 Watt bulb, it sits spinning on a stream of compressed air. (Neat-O!) Later ones used a glass rod attached to the bulb that spins which was less trouble-prone. The big point on these bulbs is that they are VERY close in spectrum to our Sun around 10-11 am in the morning.

The Air & Space museum in DC used two of these to power a light pipe that illuminated their huge front room. I don't know why these disappeared from the marketplace. They are probably not cheap, but (1) 5,000 W sulfur bulb does the work of about (20) 1,000 W HPS lamps.

Here's more on the sulfur bulb:

http://www.kbmorgan....hbull/bull6.htm

Genius DIY'er:
http://www.youtube.com/watch?v=okku7DiS9p4&feature=related


SHOULD HAVE TOLD ME TO PUT ON MY SHADES!!!!!!!!!!!! :cool:

#19 Proud Marine Dad

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Posted 25 May 2012 - 11:49 PM

It depends on how many watts the CFL provides.
Based upon my experience, with 40W CFL the minimum distance might be 4 inches (8-10 cm.).
Stronger lights might require at least 6 inches (15 cm.)
Best practice is to set up a distance and after 2-3 days have a check on the seedlings to detect the presence of dark spots on them.


I put the fluorescent lights about 1" from the seedlings and sometimes closer.

My son makes Marines. What does yours do?


#20 chilliasylum

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Posted 29 May 2012 - 06:13 AM

I have a question for everyone who is growing using hydro
Do you find your chillies are hotter?
How much chillies do you grow per month? Kg's?
Do you grow all year around?

Edited by chilliasylum, 29 May 2012 - 06:13 AM.





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