Hey Dude, Scotty and Guru!
Coming at you from the legal land of Michigan (AKA “The Mitten”). I found your podcast about a year ago and have been listening daily ever since. I love the work you guys do!
I have only been growing cannabis since January 2020. I have a few questions about par limits of cannabis during different grow stages. I am working on my second grow ever and want to maximize my yields. What is the optimal PAR for veg and for flower?
This is all pretty new to me and I am looking for some pointers.
PAR is a measurement of spectrum. You can’t typically change the spectrum (PAR) of your light (some lights can) but you can change the intensity or ppf/d. You want as full of the spectrum as possible. It’s the ratio tuning of each color a diode emits. Color temp is another measurement for spectrum ratios. The wattage of your diodes and their spacing determines how close you can keep the fixture to increase or decrease intensity.
Dude, thank you for the info! The way you explained it makes way more sense to me than any of the shit I have read anywhere else, seriously! I think I was sweating the wrong details. Thanks!
If you are indeed asking about intensity, which light are you using and what is the footprint you are using to grow in?
For figuring out the maximum amount of light the plant can handle in a day before the point of diminishing returns, you are looking to find the DLI (Daily Light Internal)
Daily light integral (DLI) is the amount of PAR received each day as a function of light intensity (instantaneous light: μmol·m-2·s-1) and duration (day). It is expressed as moles of light (mol) per square meter (m-2) per day (d-1), or: mol·m-2·d-1 (moles per day).
https://www.extension.purdue.edu/extmedia/ho/ho-238-w.pdf
I am using a Mars Hydro TS1000 in a 3×3 tent. Thanks for the info! I am checking out the link now. This is the information I have been looking for! Thank you!
Here’s a good guide with different co2 levels and stages of growth.
https://www.google.com/url?sa=t&source=web&rct=j&url=https://fluence.science/wp-content/uploads/2018/11/Fluence-Photobiology-Guide-2019.pdf&ved=2ahUKEwjE_9bKvbLqAhUCOKwKHRwBBGIQFjAAegQIBRAC&usg=AOvVaw0ePaBOpgUgskT419l_6hNe
Holy shit! This link is a science class and…. I love it!!! This is what I have been looking for!
I want to be around 1000ppfd by the second week of flower. A mature veg plant can handle that light intensity. The issue is keeping up with the plants environmental and nutrient needs. I’m generally at 500 ppfd for seedlings and small clones, and I will slowly increase every few days. At flip I’m around 750ppfd. By week two of flower 1000 or more.
Read the plants for light stress. Also look for yellowing leaves and micro deficiencies on the top leaves while the lower leaves look lush and green, a good sign you’ve gone past the light intensity the plant can handle.
I’ve honestly never owned a nice light meter of any kind. I’ve never felt I’ve needed to read those numbers when reading the plant is what matters. HPS was a no-brainer, but LED is diff game with all the different diodes. The main thing to really understand is the intensity of light a plant can handle will increase up to a point. Genetics plays a major role. A high ppfd, like 1000+, has to be acclimated to over time indoors under artificial lighting. Too much or too little, like nutrition, will effect growth in different ways. It’s all about balancing all the variables as their numbers increase as the plant increases in size and needs. There are general rules of thumb based on the environment a plant evolved in. Equatorial plants tend to do worse under intense lighting than an Afghans and vice versa. Hybrids can lean either way. Hybrids are the norm so you gotta test a plant’s limits through every stage. The initial signs of stress will become obvious over time and it’s not a big deal to ride the line after some xp. It’s a balance between intensity stress and stretchy plants.
I’m with mystro. The plants tell you either yes or fuck no. I do it with my tents all the time… Turn the light up to like 75%.. if they taco up all crazy then I know I need to ease off, if they look good and healthy I’ll crank it up a bit and monitor again. All strains are different.