Making Informed Lighting Choices

[WilliamClarkeQuantrill]

I thought we might discuss the different considerations one might take into account when making decisions on which light type to use for cultivation of HGB. As lighting is the biggest investment and some confusion seems to reamain about the way bulbs are marketed and how plants react to or utilise different spectrums of light.

I'd like to list and define the terms used when considering light and plant physiology. Some I believe are important are: lumen, CRI, CCT, PAR, spectrum, photon, photosynthesis,and plant morphology. If you have any to add, please do. I am slow, but I will work on definitions hopefully we can understand and interpret.

Is anyone interested in this kind of discusion? :smokin:

[Fred Lemonjello]

Excellent topic Q - I sure would be interested in following along to learn a little sumthin and contributing as my knowledge increases.


Fred

[Fillabong]

I am interested in discussing this topic:) Can't say much now bro but I'll chime in later:)

[WilliamClarkeQuantrill]

Great, thanks for your interest guys. I will work on the definitions this weekend and try to get them posted soon. :smokin:

[WilliamClarkeQuantrill]

Well, writing a dictionary wasn't any fun. muwahahahahahhaahhaahaha Seems every definition had a word in it that might need to be defined, so I scratched that idea.:rolleyes:

Lets just see how this unfolds.

What is it we are looking for in horticultural lighting? Its energy to fuel photosynthesis (http://photoscience.la.asu.edu/photosyn/education/photointro.html) primarily. Light is a form of energy, to understand what it is about light that makes it efficient at fueling photosynthesis you have to understand the electromagnetic spectrum. This is basically just a grouping of all forms of electromagnetic radiation arranged according to the amount of energy contained in the radiation. The shorter the wavelength the more energy. Here is a good graph showing the entire spectrum of electromagnetic energy.
http://www.homegrownbud.com/forums/attachment.php?attachmentid=3151&stc=1&d=1144800563

All electromagnetic energy has three basic properties. They are wavelength, frequency and energy contained.

Think of light as traveling in waves, like ripples on the water surface, with peaks and valleys. The distance between two consecutive peaks is the wavelength. This is a measure of distance, so we use meters or more specifically nanometers. 1 nm = 1 billionth of a meter (10^9 meters) the wavelengths of light that are photosynthetically active range from about 400 nanometers to about 700 nanometers. Light radiation with a wavelength of 400 nm is percieved by the human eye to be violet in color, 700nm light is percieved as red. Combined together light energy from all the wavelengths from 400-700 is white to the human eye.

http://www.homegrownbud.com/forums/attachment.php?attachmentid=3152&stc=1&d=1144801581

The number of these light waves that pass a given point in space during a specified time interval is the light's frequency; consequently, frequency is a time based unit. Frequency carries the units "per second," but we use a special term for the unit called - Hertz (Hz), where 1 Hz corresponds to 1 wave/second, so 60 Hz would mean 60 waves/second.

The shorter the wavelength the faster the frequency.

According to the quantum theory (http://searchsmb.techtarget.com/sDefinition/0,,sid44_gci332247,00.html), all energy is transmitted and absorbed in discrete particles called quanta or photons. So, the smallest amount of radiation energy that can exist is one photon.

For our purpose, think of a photon as a packet of energy. Let's say that light travels as discrete photons along a wave. Visible light is a mixture of many photons with different wavelengths. The photons are reflected and absorbed by various surfaces, and when they reach the eyes, they create the sensation of sight and resultant perceptions of color and brightness. These photons are also directly responsible for photosynthesis in plants. The energy from the photons is used during photosynthesis to convert CO2 into sugar, which is a primary energy source for the photosynthetic process.

Like I said the energy carried by electromagnetic radiation is contained in the photons that travel as a wave. According to quantum theory, the energy in a photon varies with its frequency.Energy is measured in units called joules.
As the frequency of the radiation increases (wavelength gets shorter), the amount of energy in each photon increases.So a photon of 400nm violet light has more energy in it than a photon of 700nm red light.


More to come... :smokin:

[WilliamClarkeQuantrill]

Blah blah blah....

Ok, so we know how light is characterized. Now lets see how bulbs are characterized.

For the most part bulbs are characterized in terms related to the human eyes response to visible light. Lumens (flux weighted to human eye response curve), CRI (color rendering index is a comparison of the color of objects under artificial light and under natural light), and CCT(correlated color temperature is the comparison of the color of the light as perceived by the human eye and a theoretical plank radiator which changes colors at differing temps) are all designed to offer information on a bulbs ability to provide light that is visible to the human eye and its color as seen by the human eye. However we are not at all concerned with the human eye when it comes to cultivation. For this reason we can not rely on these common ratings for bulbs to provide us with information to choose which bulb is best.

We want light that will fuel photosynthesis. So we should be interested in two things in light. The total energy output of light within the 400-700 nanometer range, which is photosynthetic active radiation(PAR), and the intensity at each wavelength as shown by the spectral distribution graph. With these two characteristics and knowledge of our plants response to different light we can make informed decisions on which bulb is best, or better anyway. Unfortunately PAR ratings are rarely given on bulbs not specifically marketed for horticultural use, and SPD graphs can be hard to find as well. So we should be adamant in our request for such information when we are searching for new lamps. If we the consumer make it clear we want this information ,the producers will find it in their best interest to supply it to us.

[WilliamClarkeQuantrill]

Here are three different bulbs spectral power distribution graphs overlayed each other. All three have the same CCT, but have drastically different SPD's, it should be obvious that each bulb is going to get diff. plant responses. So please do not rely on CCT/kelvin rating to choose horticultural bulbs.


http://www.homegrownbud.com/forums/attachment.php?attachmentid=4261&stc=1&d=1149687785

[Fred Lemonjello]

I'm still with ya Q..... I must say you've done an excellent job at explaination and definitions.... albeit I'll need to re-re-re-read it a few times to fully understand/ comprehend. But that's jus me... *stoned* :p
:smoke1:

Fred

[WilliamClarkeQuantrill]

Let me know if I can clarify anything or if you have any suggestions or questions. I don't mind re- writing it so that it makes more sense, if need be.

I think i will move towards the different plant responses to different light spectrums and the what to look for in bulbs to cater them towards certain responses.

It'll probably take me as long to get the next post up as it did to get these up though. :smokin:

[Dooby420]

Thanks for the help bro :D
This will surely be a most informative thread

-DooB

[drumin]

Hey Q, so if I understand correctly the Daylight 5500k bulb is a very good buld for plants due to it's high energy output in the 400-700 range. It looks like this is a 40w T8 fluoro bulb.
Do you have an SPD for MH and HPS bulbs?

Would these T8 bulbs provide enough energy for plants to veg plants? My plants get full sunlight during the day so I just want to keep them growing at night when I bring them in.

I understand that I should use a HPS for flowering.

[WilliamClarkeQuantrill]

Hey drumin,
You need to look for the specific spd graph of your exact bulb. You can't use one general one for all hps or mh or any other type of lamp.

If you can give me your bulb make and model I'll try to find a spd graph for it.

T8 flouros are pretty good flouros, i use some for the first week or so of veg, but rely on a hps for the remainder, what ever length that may be. They will grow some very healthy plants, but you can't get the growth rate/speed from a flouro that you can with any HID, in my experience. I actually even overdrive my t8s so they are even brighter than conventionally wired fixtures. But I know you can get very good results from flouros, I have seen it time and time again. It's just a matter of your taste or style of gardening.

In your situation, flouros will do a splendid job of extending the photoperiod.


toke it easy. :smokin:

[CB]

say Q



If you can give me your bulb make and model I'll try to find a spd graph for it.



cant ya just post up a graph for all the bulbs out there :p

same as Q says bro....flo's will get the job done no prob..... seen to many grows done with em say other wise :D

how we did it in the 70's :peaceman:

grow on

[drumin]

What do you guys think about this light?

http://cgi.ebay.com/600-watt-HPS-FULL-HOOD-GROW-LIGHT-400-1000-w-MH-opt_W0QQitemZ250000407715QQihZ015QQcategoryZ42225Q QssPageNameZWDVWQQrdZ1QQcmdZViewItem

Is this a good light and a good deal? 600watt and a spare bulb...

[WilliamClarkeQuantrill]

that guy is quite the salesman, i thought he was never gonna stopp his pitch. Not a bad price, but I don't like the reflector very much and not real fond of the 600 watt bulb in general.

[drumin]

that guy is quite the salesman, i thought he was never gonna stopp his pitch. Not a bad price, but I don't like the reflector very much and not real fond of the 600 watt bulb in general.
Could you elaborate a bit on what you don't like about the relector and 600 watt bulbs?

[WilliamClarkeQuantrill]

it is gigantic, is flat above the bulb (which is sure to reflect some light back at the arc tube, very bad) and has a mirror finish instead of a pebbled finish and has no means to vent it.

The 600 watt bulb is not very common in the US except for horticulture, so it can be difficult to locate especially locally. The specialty bulbs like the hortilux arn't that good in the 600 watt size compared to the 1000 watters. Replacement bulbs cost almost or sometimes more than a 1000 watter.


but its your call :smokin:

[drumin]

I appreciate the info, knowledge is power! ;)

I get what you are saying about the bulbs. What does a pebbled vs mirrored finish do for you? Does a pebbled finish refract the light better?

[WilliamClarkeQuantrill]

The pebbled finish distributes the reflected light better over the coverage area than the mirror finish does. The mirror finish has a tendancy to focus the light more on one spot than over the intended coverage area. So instead of having a pretty even coverage over say 4 foot by 4 foot you get a spot or few that have more light than others with in that 4x4 area, or even outside that area.

I'd keep looking, there is bound to be a good deal on a quality reflector, I've been lucky enough to get a hydrofarm radiant reflector and ballast for only $150 off ebay before. it was used but is such quality that I would gladly pay more for it used than some new stuff I've seen on there.

[drumin]

Hey what do ya'll think about this light, I know it doesn't have the "pebbled" finish on the hood but ya can't have everything!

http://cgi.ebay.com/NEW-High-Pressure-Sodium-400-watt-HPS-Grow-Light-w-400w_W0QQitemZ7775354621QQihZ018QQcategoryZ42225QQ cmdZViewItem

[WilliamClarkeQuantrill]

looks pretty good to me. :smokin: for a 400 watter anyway;)

[CB]

same here..... gotta love the sales pitch tho:rolleyes:

[WilliamClarkeQuantrill]

Here is an excellent tool for comparing lamps intended for horticultural purposes. Much respect to knna for creating it and sharing it. He said I could post it here for everyone to use :smokin:



To come up with the input data you need a copy of the SPD graph, the initial lumens, and the total system watts(bulb and ballast).

With the SPD graph we need to lay a grid over it to give us the ability to accuratly compare the peaks at various wavelengths. knna suggests using a graph sized so that 3 boxes equals a 5nm distance across the horizontal axis of the SPD graph. Count the number of boxes vertically to reach the peak of the spectrum at that nm, and average the 3 vertical columns per 5 nm range. Input this average height per 5 nm range into the spreadsheet at the corresponding nm.(did that make any sense?)

With this data the sheet will do the calculations and provide information to compare lamp's relative ability to fuel photosynthesis, like bulb efficiency, total micromols of photons emitted and their PUR (Photosynthetically Usable Radiation) value. It also computes the lamps PPF (Photosynthetic photon flux) and PUR value per system watt (the most relevant data when choosing a lamp for a grow) and per Klm and also gives some valuable data about other concepts (red/blue ratio, total blue light emitted, near and far red output...) that affect different plant morphological responses, like stem elongation and flower initiation.

Enjoy it.

I'll be adding a bit more as time allows, and my understanding improves.

any questions, just ask. :smokin:


This sheet is designed to calc photosyntetic efficacy of each bulb. It dont calc the "best light", because there are qualitative issues, not computable. The more relevant is the blue content, because blue light penalize photosyntetic efficacy by two ways: have less photosyntetic efficiency and emits less photons per watt emited. But blue light is very relevant in order to grow health and productive plants. Because of this, the sheet provides the total blue emission. A reccomended level of blue is 30-40 uE/m2, but more blue have qualitative possitive effects, althoughit low the photosyntetic efficiency.

There are two mains parameters when considering each bulb efficacy for growing:

-Spectrum: emitting in the wavelenghts plants use more efficiently. The concept that explain it is PPF/PUR. As higher, better photosyntetic efficacy of the spectrum alone.

-System efficiency/Watt: the efficiency of the system bulb+ballast in converting light from the imput energy (system electric comsuption). Here is where larger differences exist, thus, its the more relevant parameter.

Until now, mixing both concepts was a qualitative analysis. The sheet weight both and provide accurate photosyntetic efficacy.

PPF/W: How many photons the bulb emits per watt comsumed. The reason to give it per watt is to do comparision between differents wattage bulbs possible and easy. The highest the better. Currently, 1,5 uE/W seems to be the line wich split between good bulbs and not so good. This is an objetive parameter, there is no any subjetive calc implied, so PPF is the main measure used in botany.

PUR/W: This is the measure of true photosyntetic efficacy. Corrects PPF for the relative leave's absortion of each wavelenght, aswell for the relative photosyntetic capacity. This is the final goal of the sheet, as provide in a single figure a summary of all the parameters implied. In order to do a list of best bulbs for plants, this parameter would be the used as a reference of best and worst. The higher the better. Any figure over 1 is good, but the 1,2 figure correspond to top end bulbs.

There is a problem with the PUR figure, as it implies a correction with the plants quantum yield, and there is no any study to compute that for cannabis, so the correction factor is calculated indirectly, so it implies some subjetivity.

The PPF/Klm and PUR/klm just are provided to compute PPF and PUR from lux data in real measurements. Sunlight is about 16,8 uE/Klm. HPSs are around 12 uE/klm, while MHs are around 14-15 uE/Klm and standard floros between 13-15 uE/Klm.

The Red/Blue ratio is provided to help in qualitative analysis. Its difficult to say whats the best. Anyway, it depends of the plant's developing stage. NASA scientifics works with R/B of 9 as optimum, but it probably depends of the plant specie. I believe any ratio below 10 is good for vegetative stage, preferably in the 3-6 figure, while in flower it depends of the total irradiance used, but a R/B ratio between 8-16 seems good. As general guidance, as higher the irradiance used (uE/m2), the R/B ratio must be higher.

Peace and good grows

Dude, You Rock!


Ok, so PPF gives each photon an equal weight? and PUR tries its best to give accurite weight to each photon according to marijuana's ability to use it for growth?

If I have a light meter, I can use its measurements in photmometric terms in conjunction with the PPF/Klm and PUR/klm data from the spreadsheet to calculate the actual amount of energy falling on any given spot in the grow?



Yes, PPF is Photon Flux, is a count of photons, simply. The unit uE is equivalent to micro mols of photons. A mol of any thing is 6,0221415*10^23 (yep, a 6 followed by 23 zeros) particles, in this case, photons. A micro mol is the 1/1000000 part of a mol, so each uE is about 6 followed by 17 zeros photons per second.

PPF relates to bulb emission, an absolute measure. Another thing is how this photons reach the plant, the irradiance, wich relates to the surface receiving the light. This is the measure wich changes depending of the bulb distance, with no reflectorized bulbs, it decreases with the square of the distance (square law). This measure is Photon Flux Density, PPFD, wich correspond to uE/m2, its one radiometric equivalence of flux, wich unit is the lux (=lm/m2), and this is what luxometer o photometer measures. To convert from lux to PPFD, just multiply it (in Klux=1000lux) by the PPF/Klm data in the sheet, and you obtain irradiance uE/m2 (what expensive photon count detectors measure with less accuracy).

PUR correspond to Photosyntetic Usable Radiation, its a adimensional measure, as its PPF weighted by plant's absorbance and photosyntetic action of each wavelenght. I use "pur" as "unit". PURD can be obtained from lux data the same as PPFD, multiplying the Klux measure per sheet's PUR/Klm.

Why obtain this adimensional data? Because its the measure wich can give an accurate measurement of light used in a grow, independ of the kynd of light used, opposite at PPFD. Give up watts/sq ft, lm/sq feet, whose indications are only valid for one type of light and wattage.

We can say: MJ needs 20000 (=20K) purd in order to flower. MJ reach its maximun photosyntesis capacity at 30K purd, and reach saturation point at 60 purd (these are improvised example levels, apart each strain is a bit different in this), and these are valid data independent of the light used, in quality and wattage: for example, an average 30K purd at canopy can be reached with a 400w HPS in 15 sq ft, with 600w of 32 w of CFLs, or with 400w of T5s floros (again example invented level). The sheet is the tool to calc how many watts of the light we are going to use are needed to reach the PURD level choosed, or calc the grow area a specific bulb can cover at the PURD desired level.

Astract: yes to the three Quantrill questions