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The Pro Grows: Blue Gelato by Barneys Farm – The 100l experiment

Why you should grow Blue Gelato 41

Derived from Thin Mint Girl Scout Cookies and Blueberry the Blue Gelato is another US based import to the European market under the distribution of Barneys Farm. The strain contains that mainly sweet and citric taste that Gelato is known for. Underlying with OG and Blueberry flavors you will get a …

(here I rolled a fatty to experience it another timer)

38°C on my balcony. The wind feels like a desert or caribian breeze. It all started with the selection of the particular flower. I decided to use one of the many top headbuds. The curing process was only three weeks in, the flower was as gluey as it gets and showed an incredible trichome density.

The effect delays into the second or third hit, subtle first but exponentially transforms to a truckload into the back of your head very quickly. The high is longlasting and top heavy. Side effects for me are a dry mouth and a big urge to eat some hot and spicy food.

(here I took another break to rest on the couch with some ice tea)

Items and tools

TL;DR – Blue Gelato 41

  • Strain: Blue Gelato 41 by Barneys Farm
  • From seed to weed: 141 days (veg 84 days, flower 57 days)
  • Wet harvest weight: n.a.
  • Final Dry yield: 244 gr (8.6 oz, single plant)
  • Effect: Strong, head heavy, numb mouth, clouded mind, psychedelic
  • Taste: sweet, OG, pungy

The Grow

Germination and Seedling Stage

When growing from seed you should always germinate more seeds than the actual number of plants you want to grow. Since I wanted to have one single huge plant I germinated two seeds and simply used the first one to show up as the main plant.

cannabis seeds
Blue Gelato 41 seeds

After about 0.5 cm of the initial root showed up, I put the seedling into a 3 gal smartpot with a fresh batch of BioBizz Lightmix. The first two weeks of a grow are always slow and boring: You dont really need to do anything but sit and watch. I kept the soil moist with my sprayer to prevent the seed from tilting from too much water. After the stem was strong enough, I turned to my usual watering schedule. This is also the point where I first give the seedling external nutrition. Lightmix already comes with a good amount of plantfood but for the remainder of the vegetative I gave her 2 ml of Bio Grow and 2 ml of Bio Heaven per liter of water. As usual I lowered the pH of my water dwon from 7.8 to the region bewtween 6.2 and 6.5.

Small cannabis plant in soil
Seedling a week after germination

Vegetative Stage – the long training

As you might know, I count the seedling stage into the veg stage. So the day my seeds get hit with water, I start counting veg days.

After 18 days the plant was ready for the top. I topped her once with intend and a few times by accident. I topped the plant right above the second node, so I ended up with four main branches, that will be trained outwards.

Cannabis plant in vegetative growth
After 18 days this plant was ready for an early top
topped cannabis plant
4 tops are left to be trained outwards
topped cannabis plant with LST applied
After three days the tops are ready for the bend!

Training setup is done! For the rest of veg I just had to train the shoots outwards again and again. four weeks into vegging I transplanted the plant into its final container: A single 100 liter unit! I decided to give her eight weeks to root through this volume.

Transplanted cannabis plant
Blue Gelato 41 after one month since germination in its final pot.

For this particular plant it was necessary to remove several side branches while it got trained further and further. The internodial distance was just to short, and even with this premeasurement the plant ended up being a nasty bush nontheless.

cannabis plant in a big pot
Bushy plant that needs some trainin…. (6 weeks old)
cannabis plant in training
…and after appyling LST (same day)

I wanted to play that out as far as possible and ended up with a structure that looked more like a weird piece of art than a plant.

heavy LST applied to plant
Heavy LST applied to a cannabis plant results in this structure. (8 weeks of veg)

The branches and the stalk are getting fatter by the day after 8 weeks of veg. The plan was to let her grow to the walls of the grow room and then upwards to encourage a bit of stretch once shes sent into flower.

cannabis plant and a ruler
My plant is 15cm tall after 10 weeks of veg.
upskirt shot of a cannabis plant
This shot shows what you have to deal with when doing something like that.

A few words why this method of growing cannabis is actually pretty dumb: So my grow room would be on top when it comes to economical grows. I use very efficient LED lights and do not bother with AC units or anything that impacts my electricity bill alot. I am still growing with under 400W of total power. But having a plant in this environment for that long kind of kills the idea of being economical here. Time is an important factor when it comes to economical growing, and what was done here was the opposite. The grow itself took close to 5 months to finish, while its possible to harvest more in just 3.5 months.

Flowering the beast

After 84 days of veg I pulled the trigger and started flowering. The branches did not really hit the walls of the grow room, but I thought the flowering stretch and a little bit of spreading would take care of that. Note that I defoliate pretty conservativley before flowering, which cant be seen here exactly, but my goal is, that every top gets direct sunlight.

huge plant
Blue Gelato 41 starting to flower.
detail shot of early flowers
Cannabis flowers in the earliest stage of development.

But I was wrong here: the plant had to support about 50 to 70 tops and stretching was not something she wanted to take care of. My assumption is, that the potential to stretch decreases heavily with the amount of top to put energy into to stretch. I got about 5 cm extra height overall, and thats it.

With the development of flowers, the plant now needs different supplements. So I switched from grow to bloom nutrition according to the BioBizz nutrient schedule sheet. I watered the pot with 10 l of water every 3rd or 4th day. Hitting day 21 of flowering I went for another round of defoliation, but I figuered out soon enough that this would not be enough for that lady. She kept putting out leaf material by the day, and I could grab handfuls of leafs far into the flower cycle. Most of the leafs on the back of the plant could not be pruned because I simply could not access that area at all…

cannabis flowers in development overview shot
Blue Gelato 41 in flowering.
macro shot of cannabis plant in early development
Resin production began early and heavily on that pheno.

Whenever you hit week six of flowering theres not much to do but checking trichomes and soil moisture.

maturing cannabis plant
Flowers of Blue Gelato 41 near the finish line

Although I had to deal with leafy colas the resin production on that strain is insane! After only 20 days of flower the colas were packed with trichs and after only 46 days I could already see trichomes turn amber.

trichome shot of cannabis
Day 46 of flower and the trichomes are already turning amber and are mostly milky. This one will be a fast runner!
cannabis plant closeup
Blue Gelato flower

Harvest, Drying and Curing

macro shot of harvestready cannabis
Brown pisitls, milky trichomes, and a good portion of amber ones: this lady is ready for harvest

So after only 57 days, six days before the harvest window given by the breeder, I decided to cut her down. Not only because she was ready, but I had to fight high temps in the grow room, and I did not want to risk any mold since that bush was so dense! pulling out a 100l pot out of that room was a pain.

bushy cannabis plant
The leafy backside of the plant, that I never had the chance to defoliate.

I decided to dry trim this time. So I cut away most of the fan leafs and hang her up branch by branch. After 7 days of this initial drying it was time for manicuring. This is mostly done by removing everything thats not flower material. But since the resin production of that one was so incredible dense I decided to keep a lot of sugarleafs on her. It was a rather experimental run in the end and I would not do it like that again, but a worthwhile experience!

cannabis dried and ready to smoke
Curing Blue Gelato 41

Topping

Topping is an invasive training method. Contrary to Low Stress Training a plant needs a significantly longer recovery time from an amputation, which sounds reasonable.

Timelapse of a topped cannabis plant

As you can see, the plant is developing more than one main branch. This happens due to the amputation.

The right moment to top – mainline or spreading

How to top cannabis plants
The topped plant has already established very noticable side nodes. These will be the new main Branches

The right moment to cut of the head of a young cannabis plant is to choose carefully. What to you want to achieve? If you want to spread out her sideshoots you can wait until two weeks before flowering to cut off the main. The plant will distribute more energy and growth into the sidebranches which will develop much better after that. So you end up with more thicker branches at even height which will also optimize growth overall. Growers who do that, like to top a bit later into the vegstate (after the 5th node) and refrain from low stress training in the way to let the shoots go upwards.

Example of a topped autoflowering plant
Autoflower that got topped without mainline. source

Mainlining your plant has a different approach: Its more of an artform and maintops will be developed in a more symmetrical manner. The topping has to happen much earlier in is my favourite approach to HST or high intensity stress training. It combines HST with LST very early on in the life cycle and gives you the ability to guide the growth of the plant in a more detailed fashion. It also let the plant stay small and bonsaiesque which is favorable for small grow spaces with low heights.

Mainline branches
Plant that got topped and put under LST at least twice. This results in 2^2=4 shoots.

Mainlined plants are split up immediatly with next to no internodial growth. That results in a distinct number of tops: If you cut away the mainshoot n times you will end up with 2^n mains.

triple mainline
A plant that got topped a third time, resulting in 8 main shoots.

Pros and Cons of topping

First of all topping costs time. Flowers need to heal up of that for about two weeks before you can think of switchting them to flower and establish a healthy branch structure again. You will end up with a more even canopy, can bring the light lower and will ultimately get more yield since more buds are in close proximity to the light source. Mainlining takes even more time than just a single top, but you will be able to shape your plant in various ways because all fresh branches are still young and flexible.

My recommendation: Take your time and let her veg for 2-4 weeks longer. You wont be disappointed in the end.

Topping Autoflowers

Yes, topping autoflowers is definetly possible. The best strains to try this in are the ones with a longer life cycle like most sativa dominant strains. The moment of the amputation has to be crucially timed tho. If you think the plant is already about to strech or shows early signs of sex, you should refrain from it. The time window to properly top an auto is pretty thin. Be careful here. But as I said: Its worth it in the end.

A mighty cannabis flower
If done right you will end up with a massive canopy of donkey dicks! (This is not an autoflower.)

Defoliation – Make way for the light

Buds tent to develop best, when hit by direct light. If a bud is overshadowed by big green fan leafs the bud will develop not as good. Defoliation is the key to make the most of your plant and maximize flower development.
This grow tech requires a bit of experience and knowledge of a Cannabis plants structure. I do not recommend this if this is your first grow. After a full run, without removing leafs you will know exactly what to look out for the next time.

There are growers out there removing nearly every fan leaf that a plant grows after 21 days and after 42 days of flowering. This is called schwazzing and a rather extreme manipulation technique. The other extreme is to remove nothing. My way of defoliation will remove a lot of leafs in the process, but will leave a lot of leafs for the plant. Its kind of a middle way.

The Pros way: Moderate or selective Defoliation

Not every plant needs to be defoliated the same amount. There also no godly plan to defoliation for all the plants.

Defoliation in the vegetative state

If you have a very bushy indica dominant strain or applied a lot of LST to your plant it will potentially grow very bushy. In extreme scenarios only a few leafs on the top of the plant will be necessary to build up a full canopy.
This is not good if you want to encourage branches under there to develop!
Remove the big fan leafs from the top of the plant to make sure that budsites below get direct light aswell.

freshly defoliated plant
Freshly cut plant: Fan leafs from the top of the plant got removed
recovered from defoliation, new growth is visible
New growth after three days: The gaps have been closed by new branches taking the spot.

How to check if a certain fan leaf should be removed:

  • If the fan leaf creating a shadow to budsites below remove it.
  • If the fan leaf is growing “inwards” or growing bigger and bigger, remove it.
  • If the fan leaf grows at the edge from the plant away, it can stay.

This way you will remove the leafs very selectively and keep the plant not as stressed out. Its also not feasable to potentially stun the plant because you removed so much.

Defoliation in the vegetative stage can be tedious since it could be applied about every third day from a certain plant size on.

Defoliation in the flowering process

This is pretty similar to the vegetative state. Since the plant will still grow new green material, remove the leafs that steal light from buds. Just look closely at every bud and check if there is a leaf above. Remove all the leafs. From about week 3-5 the green development of the plant will be reduced because the plant packs more supply into the flowers. Your work is pretty much done then regarding defoliation.

Extreme Defoliation: Schwazzing

Widely in use by certain industrial grow operation schwazzing is the process of removing nearly every fan leaf that grow on a plant at the beginning of the flowering stage, leaving only the top of every budsite intact. This method also involves some kind of lollypopping since every side branch is pretty much removed as well. Just leave the first 2 to 3 nodes from every branch intact.

Timelapse video of schwazzing in an industrial grow setup. These operation have a lot more light power per squaremeter than a common homegrow. The lights can penetrate much deeper! Schwazzing a plant makes sense here.

Chocolope that got alot of nodes removed, leaving up only the top of the plants, sortly before flowering.
The same plant in flowering: Branches full of buds!

Additional notes

I would not recommend schwazzing for every strain out there. There are alot of cannabis varieties that are able to put on serious weight on the side branches where you would harm more than you do good if you remove too much. Branchy indica type plants are very much content with selective defoliation while some other plants like to be cut more heavily. I suggest you.

Lemon Zkittle that got exposed to defoliation: You can see through the branching to the other side of the pot.
Alot of Budsites are directly visible from the topview, since the light now got a free way down there.
Areas that wont get direct light will be cut most.

Defoliation is a pretty harmless tech, since a plant will develop way more fan leafs than needed to survive. A grow tent is also an environment where the plant is enclosed and save enough so that it can deal with this harm without having to fight pests or difficult weather patterns while at it.

Setup for the Avid smoker – The 3×3 grow tent

Grow tent in full flower
You can do this, with a setup described in this section. Source: homegrow-pro.com

Everything you need to harvest  10 oz. of dry material every 3-4 months!
I will list the items that are absolute mandatory to grow first. There is a list with additional items, that I deem useful below. Get started on your first grow tent!

General Assumptions

  • Your grow medium of choice is soil.
  • You grow in a grow tent.
  • You start from seed.
  • You are a grow enthusiast who wants to make the most of a given space.
  • You do not have to run this hobby on a budget. (Options for that below)

List of items

TypeItemQty.PriceLink
grow tent3×3 Grow Tent1$90amazon
light*400W COB Light 1$600timbergrowlights
pots3 gal airpots4$50amazon
soil*60l specialized soil1$15 – $30(see below)
nutrition*Trypack1$15(see below)
ventilationClip Fans1-2$10-$20amazon
filtersystemACF+fan+tube1$90amazon
clima controlTemp./Hum. Monitor1$3amazon
on/off switchProgammable timer1$12amazon
Tot.~$895
  • Tents are great to keep control of every aspect. You can change temperatur, brightness, humidity and even simulate seasons in there! Its absolutely necessary to get your tent completely dark to your needs. If you have a closet or a room where you can manage to create pitch black darkness, you dont need a tent. The brand of the tent does not really matter. 
  • Light: Your articficial sun. Good growlights are hard to find in the LED jungle. Read more about lights below.
  • Pots: They come in different varieties. Plastic, fabric, with holes in it from 0.5 to 30 gal. I choose the airpots, because they let air move through the soil, and roots are pruned naturally at the outlets, preventing root rot or rootbound plants.
  • Soil: Do not buy common gardening soil. Cannabis roots need space to roam. Specialized cannabis soil has the right consistency and is often perfectly balanced with nutrition. You can also cook your own soil!
  • Nutrition: Personal opinion about nutrition – as long as its marketed for cannabis and does not kill your plants every brand seems legit. It is more like a personal decision what kind of nutes you use…
  • Ventilation: Moving air prevents bud rot and keeps the branches moving. That creates resistance and your plant will grow thicker and stringer. Keep the vents on 24/7.
  • Filter system: Your main exchange for air. If you have to grow stealthy or at home you do not want to have the smell leave the tent. Get one of these asap.
  • Clima Control: Really important to keep track of your values in there. You want to know the numbers. Once you know its over 34°C in your tent all the time, you know its time to do something about it. Same with humidity.
  • On/Off switch: Over the course of 100 days of a grow you dont want to hit the switches twice a day at the same time. Automate that.

*

The light

Yes, the light is the most expensive item in a grow operation. Yes, you can save money on light, but this is the best option for a grow room of that size. Its cool, quiet and runs damn bright. It has the most recent technology behind it and does not need extra cooling. But there are alternatives.

PRO TIP: You need at least 35W/ft² of high quality LED/COB light or at least 50W/ft² if you use CMH/HPS lights, if you want max out the tent potential! There are thousands of options. Just make sure its a grow light. Spectrum, PAR, PPFD values and color of light are also important properties. Read everything about the theory behind light here.

Alternative 1 – The Quantum Board

Horticulturelightinggroup.com has a very decent 320 Watt kit. It has alot of advantages like better light distributions or overall efficiency. I just did not link it as first option because it only has 320 Watts, and we wanted to get the most of our room with the given conditions. If you are able to build these lights yourself with a kit, buy these! The magic behind Quantum boards are LM56c or LM301b LED chips from Samsung. If you can find other distributors using these chips, you can go for it.

Grow tent with a quantum board
Quantum boards have an exceptional efficiency and overall light distribution!

Alternative 2 – Other LED Distributors

Its true, Timbergrowlights is just an option when in comes to LED lights. There are several chips out there that are awesome to grow weed with.
Timber makes use of Citizen CLU048, Cree CXB3590 and Vero29 COB LEDs. But other companies do it aswell!
Cobshop.net has a 3×3 kit including 4 COBs for $480, but they dont disclose how many Watts you get in the end. I assume its 200 W, so only half of my first option.

Alternative 3 – Low Budget only

I will list them here only because they work. But do not expect wonders. Im talking about the infamous blue/purple or pink lights you find on amazon.
NO, they almost NEVER deliver the amount of power they have in their names, NO you dont need just one, but at least 3 of these “300W” varieties you find online. Which one you take does not really matter, they are all ok. They only use the cheapest LED technology, including chips and drivers. If you spend $210 on three of them, you will be able to light up your tent properly. But remember to tune up the ventilation system, because three of these bad boys run pretty hot in a 3×3.

Blurple light tent
Blurple lights – They just won’t leave me alone! Low costs – low yields.

Alternative 4 – HPS lights

A 600 W HPS light will get you pretty far in a tent like this. And it costs only $130. This can reduce the inital cost significantly, but keep in mind that these light run HOT. And by that i mean shit-i-might-need-an-AC-in-my-tent HOT. The price is low, but running this shit can cost you! Save some money, ditch the AC and the pay only 2/3 to run a sweet LED light in there and pay less for your production.

Alternative 5 – Build your own COB or Quantum Board light

www.ledgardener.com, is the best source for that. There will be a guide here soon….

Soil and nutrition – Globalization and availability

If you live in Europe you have different soil companies than in the US. So while you can buy BioBizz in Europe pretty cheap, it is better to choose Fox Farm. 

The right soil is very important for your grow. Your roots want a pretty loosy, oxygenated environment. Many soil companies put peat (turf) in their soil which is very harmful to the environment. Check the ingredients, if you want to save the planet.

EU soil recommendations

US soil companies

Nutrition

Same with as soil. It seems like there is a new nutrition company out there every week. Even the breeder try to jump on the nute train and handing out their own nutrition along the seeds. (Royal Queen Seeds and Green House Seeds for example.)

I will also only recommend nutrition that have an organic base. I just do not believe in chemicals, but thats up for discussion.

EU nutrition recommendations

US nutrition recommendations

Useful additions

There are a lot more items making your tent easier. These are nice to have, but not 100% necessary. This list is not not yet completed.

Pre-grow

  • Depending on your method of germination you will need papertowels or kitchen paper.
  • Since germination needs a dark, moist and warm environment, you might need a propagation box. I just put them in an old cookiebox on my PC.
  • Do not touch seeds! Use a tweezer.

Seedling and vegetative stage

  • Seedlings do not need flooded with water. Use a pump sprayer and be careful!
  • If you plan to train your plants, you need gardening wires or metal stakes. Or anything else you can come up with. You can also just use a cord and bind them down.
  • Use sharp scissors, knifes or even scalpels to cut leafs!
  • If you see pests like mites or thripes, treat them with bio degradable organic insecticide. Be careful with that!

Flowering stage

  • Some genetics produce fat buds. Too fat to hold them in place. Use plant yoyos or bamboo sticks and wire to hold them in place.
  • If you see any pests in the flowering stage do not spray the buds with insecticide. Use predatory bugs to fight them. This is your chance to have a personal ladybug army in your garden.
  • Jewelers loupes help you watching the trichomes and help to determine the harvest window.

Harvest, Drying and Curing

Grow Lights – Theory of Light

In this chapter you will learn about the different aspects of light in gardening. It clears up all the different keywords and hopefully all technical terms that occur when talking about light.

Definition of Light

“Light” is actually defined as a thin part of the electromagnetic spectrum. Exactly the one we can see with our human eyes. 

Light can be divided into parts called photons, which act in theory as light particles. According to physics you can treat light as a particle and a wave simultaneously. We will need both ways in this chapter!

Short wavelenghts means high frequency. Higher frequency correlates to higher energy per light particle. Long radio waves, which can expand to several meters in wavelength have a very low energy per photon.

Electromagnetic Spectrum with the visible part in the middle. From: Wikipedia

Defining a light source

If you want to learn about lightsources such as Light Emitting Diodes (LEDs), High-Pressure Sodium lamps (HPS), Compact Fluorescent lamp (CFL) or Ceramic Discharge Metal Halide (CMH) you will not only have to look at the specs each of these lamps have, you also have to look at the theory on which the light is created. Every single light source used for growing has its advantages and disadvantages.

All light sources used for growing work with a the same rough principle:

Turn electrical energy (input) into light (output)

The devil is in the details. As always. What I will describe now is awful lot to learn and difficult to have alook through. But its worth the reading, and after this you will be more able to decide wether a light is “good” or “bad” for your cause.

What light does a plant need?

Plants have two main sources of energy: The root environment (soil, water, aeroponics, nutrition…) and the light that shines on its leafs. The process in which the leafs turn light energy to “food” is called photosynthesis.

Not every light that a plant is exposed to, is usable to do photosynthesis. A human eye can basically see every color between 390 nm and 700 nm, but is blind for colors that have lower wavelengths (ultra-violet) or higher ones (infrared). Humans are most sensitive for the color green. As opposed to plants. Keep that in mind when you get to the unit section

Plants have a similar spectrum, but see actualy green light the least. Thats obvious, since leafs are commonly green, so they reflect the green parts of the spectrum. The three ingredients in a leaf that are responsible for the reaction are Chlorophyll-a and Chlorophyll-b as well as Carotenoids.

Bottom: Spectrum of photosynthesis rate –  There is a big dip in the middle.

Top: If you build the sum of the three top spectra, and take into account, that the different parts that are responsible for the photosynthesis are available in unequally you get the lower spectrum. Chlorophyll-a is obviously the main driver for the process.
Source: 
https://en.wikipedia.org/wiki/Photosynthetically_active_radiation

If you look at the lower spectrum in the picture above you can get a sense of what kind light a plant likes to receive: two broad bands of light between 400 nm and 500 nm and between 650 nm and 700 nm. One is in a blueish region, whilst the other is rather red. 

The Relative Quantum Efficiency

The three molecules (molecule groups) Chlorophyll-a ,Chlorophyll-b and Carotenoids are not the only driving factor of photosynthesis. In of the most cited articels from K.J. McCree (1972) he measured how the plants react to light of different wavelengths. He found, that the area around the green light (550 nm) is actually well used by the plants. Not as good as blue or red light, but up to significant margin! So green light is not inherently bad for plant growths.

Mc Cree curve showing the photosynthetic efficiency of green leaf material. The experiment is from 1972, so it might be time to reevaluate. In this graphic we see the impact of  red and blue lights in growing, but you can also imagine that green light is also important.

Measuring light – A jungle of units

Now that we have the favourite colors of a plants light dinner, we need to figure out, how much they need! This is determined by the amount of light a source can emit. This amount can be described with various units of measurement. Some of them make sense for growing (PAR, PPFD), others don’t (lm, lux), and the rest is not normalized and/or very subjective in a way that it is depending on the experimental setup one uses to measure it.(also PAR/PPFD).

The following part will enlighten you about the different units of measurements scientist and light distributors characterize light.
Note: I tried to sort the units in order if importance, starting with the most important one.

PPF and PPFD – Photosynthetic Flux
Photosynthetic Photon Flux Density

Lets dive right into things. So photosynthesis is a quantum process. Just think about it this way: A leaf is plastered with billions of little molecule-machines trying to catch light particles in the exact right energy range. The more machines are hit per timeframe the better. So PPFD counts the amount of photons (µmol) that hit a certain area (m²) in our timeframe (s). This results in the unit of measurement:  [PPFD] = µmol/m²/s

A PPFD value of 900-1000 µmol/m²/s is needed to saturate a canopy area of plants if you use a warm white spectrum!  How to get an even canopy using LST!

PPF on the other hand only counts the Photons emitted by a light source, but does not take into account any absorption effects. So if a photon is emitted through a source and runs right into a the case of the light, its counted towards PPF but not PPFD. [PPF] = µmol/s

The counted Photons also have to be from a certain spectral area between 400 nm and 700 nm. Everything else is not counted!

Two different lights: Blue has a smaller wavelength and can transport more energy per photon than the longer red. Source: http://www.shorstmeyer.com/wxfaqs/Blue_Sky/bluesky4.html

Example 1: Lets say we have two lights emitting 100 photons a second on a normalized area. One is blue, one is red. The blue photons contain more energy. The PAR value would be higher for the blue light. The PPFD value would be actually dead even because both lights emit the same amount of photons in the active range.
So which light is “better”?
Answer: The red one for flowering, the blue one for vegetative growth. This is also the reason “common grow lights” give you both parts of the spectrum which results in a pink look of the lights. (blurple if you want…).

Cannabis plant under a grow light with a blue/purple spectrum
Cannabis plant under a grow light with a blue/purple spectrum. Source: homegrow-pro.com

Example 2: We add a green light to the show with an output wavelength of 555 nm monochromatic light. Its PAR values would be better than the red light, but worse than the blue ones. PPFD would be dead even again. Do we take the green one now?
Answer: No! A green light is not effective to grow cannabis. The plants will not be able to do photosynthesis with green light, as effective as with the use of fullspectrum systems, because they simply reflect alot of it.

Grower inspects his plants with a green headlight.. Source

Conclusion: When reading about PPFD values in the description of your light, always take a look at the spectrum as well. If the light “wastes” alot of intensity on green wavelength the number is not as useful anymore! If you have a high PPFD value it can mean less if it has mostly a green spectrum.
Its also interesting to look at the light distribution a light creates at certain distances to the source and wether the source created an even output! If there is a disproportion between PPF and PPFD its often times a lack of optical diffractors that distribute the light uneven to the plants. Take a look at a HPS lamp that creates light in a very narrow area inside its tube. This creates a very uneven distribution on the surface area: Buds on the edge of the light cone will develop more poorly.

PAR – Photosynthetically active radiation

This is easy to figure out: You imagine a perfect black surface and shine a light on it. The hypothetical surface (m²) absorbs the energy at a 100% effectivity which you can measure. Within a certain timeframe we can now measure the power (W) emitted by the light in [PAR] = W/m². The counted photons are again in the 400 nm to 700 nm range.

Here is a subtle difference to the PPFD value we learned about in the last section:

Example : Imagine two light sources. One monochromatic red and one monochromatic blue one. The red one has an output of 200 photons a second with 700 nm in wavelenghts, while the blue one puts out 100 photons with 400 nm. PAR does not care if the plant can use this light, it just takes the values because they are in the range where we observe PAR. So regarding PPFD we learned that the red one should be twice as good as the blue one. But on PAR level both are about even, because the blue light can carry more energy than the red one and PAR only cares about energy over time on a certain surface.

Conclusion: PAR can be at a high value, because it gets pushed through high intesity of blue parts in the spectrum (more blue wavelengths). Always check PAR, PPFD and the spectrum.

Light distribution under a metal-halide light: perpenticular to the source direction the light is most intensive. PAR values might look good, but whats measured at a surface level is also important! 
PPFD takes uneven distribution into account

W – Real Power Draw (Watt)

The Wattage of a lamp is a good ballpark number to start searching for a light source. Its actually the first value I look at, and from there you start to compare lights on the same level!

The power draw from the wall can directly calculated into money that appears on your power bill. So this is often the first thing you want to check. After this, you find out which light converts this money to the best possible PAR/PPFD/spectrum combination.

Many light suppliers tend to market their lamps with this value to its customers. 

WARNING!
Blue/purple lights from various distributors will name their lamps after “artificial HPS equivalent Watts” to trick the customer. You might think that a 600 W LED with the an awesome blue/purple spectrum is the deal of the day. Be aware that these companies hide the true power draw in the description at amazon or eBay. And they are good at it. Don’t get fooled.
If you think you can have 600 W of high quality LED plug-and-play light for 100$ you are WRONG.

Always check for the real power draw.

  • If you’re going for HPS/CMH/Lowball LED light: Calculate with at least 50 W/ft² for decent results.
  • If you are using High-Quality LED Lights (COBs or Quantumboards): Calculate with at least 35 W/ft² for decent results.
This Phlizon is marketed as a 600W LED Grow-light for mind-boggling $89.99. Its actually a 108W shit light, thats not even suitable to light up a 2×2 tent. ONLY BUY THESE LIGHTS IF YOU ARE ON A BUDGET! This scam is actually the “Amazons choice”…….

lm, lm/W – Lumen, Lumen per Watt

Now we’re really deep down the cave. But still: Companies try to catch you with values like this! 

Lumen is one of the least scientific units around, but still has some meaning for interior architects and astronomers. The unit is an abbreviation from the units candela (which literally refers to the output of a burning candle) and the so called luminosity function.

Quote:  “[…]
luminous flux is 
weighted according to a model (a “luminosity function“) of the human eye‘s sensitivity to various wavelengths. ” (Source)

So if you are following you might wanna ask yourself something. 
First remember: The human eye can best distinguish green wavelengths, because it is most sensitive around the 555 nm value. A plant is literally blind in this region.
WHY would you buy a light only because it has awesome lumen values?!

As always: check the spectrum! If the light is mostly green it will have awesome lm values. And perhaps, if its a modern LED, also great lm/W values. But it might not really suitable for growing.

NEVER BUY A GROW LIGHT ONLY BECAUSE OF THE LUMEN OR LUMEN/WATT VALUES. THE UNIT IS MADE FOR HUMANS, NOT FOR PLANTS!

How The Pro chooses a light

When it comes to the decision for the grow lights people always hassle. The market is flooded!

  1. Determine the size of your grow area and find out how many of the sweet Watts you want in there. The unit might not mean much, but you gotta start somewhere! Example: 3×3 tents have 9 ft² of space, so we need about 315 Watts of High Quality Growers Masterrrace LED Awesome Lights, or 450 Watts of Lowball LED / Good-old-fashioned HPS or CMH lights. Make sure your light has a PPFD value of 700-1000 at canopy level, has a full spectrum (warm white) and an efficiency of 120-200 lm/W (remember that you can use this number only for lights with similar spectra).
  2. How is your budget? Great LEDs are expensive, but worth the money. Pre build ones come for $1-$4/W in various forms. So youre looking potentially at $315 – $1260 just for the light. If you want to save money you can choose low-quality LEDs for like $250 that will reach 300 Watt if you buy 2-3 fixtures. Or you just go for a HPS setup for about $150 as a bundle with reflectors and balast. (I wont go into the details here)
  3. Lower your expectations! Great, you just want to take a look into growing and chose the entry level LEDs. Thats totally fine! You can grow awesome weed with these lamps! But if you ever feel you are missing out on something, come back and read about the real LEDs.
  4. Did you really get the HPS?! Thats also fine. They are working for decades and give awesome results. Come back if you think about buying an AC unit and have nightmares about your power bill…
  5. You cant decide between two or more lights? Compare PPFD/PAR/spectrum values at the same Wattage and find your favourite! A light should at least bring the PPFD up to 700 – 1000 in the sweet spot.
Spectrum of a Mars Hydro 300 W light normalized by maximum intensity. The spectrum is good if you just consider the PAR spectrum, but misses out heavily between the red and blue lines if you take the McCree curve into account as well.

LEDs recommended by The Pro

I’m not getting paid for it (yet) but here are some lights i will approve. I saw the results from growers and if you want high yield, dense buds and fast growing weed with low internodial distances buy from them. They also tend to run much cooler than HPS lights…

Timber Grow Lights (US)
Horticulture Lighting Group (US)
Cob Shop (US)
Greenception (EU)
San Light LED (EU)
Rapid LED (US)

Build your own!

Don’t try to buy a good grow light on amazon.com