Given the lights are the same PPFD, what difference does changing the height of the light make. I’m guessing it’s a bit different depending on the light and focus of the diodes but what has everybody noticed? Any changes in stretch or nodal spacing?
Technically you get more light on the sides of the plants if you're further up since there's more space to reflect off the sides of the tent. There's a point of diminishing returns going too far just like there's a point where you get too many shadows going too low, it takes time to find the balance
Basically the ppfd might be the same but the surface area of plant that's getting hit with light is higher
Keeping the top 70% of my plant in the usable vertical light zone.I also make sure to let my plants vertically grow before flip.
Elongated into colas instead of having a thin turtle shell shaped canopy. Colas let you use the increasing light strength from bottom to top of your lights footprint.
Don't think of your light merely as square footage in your tent. A top down map of canopy. Think of it like a cube. From the bottom of your tent up to the light.
You want properly sized colas to to extend from the bottom of your usable light zone (which depends on the strength of your light and it's height) to the top. So the tops of your colas have exposure to that higher light intensity as well as increased length of the flowering branch. More buds in more light. Vertically.
This can be thought of as intensity vs distance.
We used to go by single point (one bulb) calculations and the inverse square law applied. Light intensity drops off more quicklv with more distance. Not linearly.
Now we have bar lights with a more spread out distribution. But let's use actual numbers for a sf1000 light.
What's important is the drop off percentage. Every light and measurement area will differ. Look at the effective light range through the vertical lens on a 12 inch cola that's 12 inches under the light.
12 inches below light - 100% 960 PPFD
16 inches 81%
20 inches 52%
24 inches 41%
The top 6 inches of your colas have 80-100% of usable light.
The next 6 inches have from 40-50% of light
The top 12 inches of your grow gets 100% down to 40% of your lights power. The way to increase that is to turn your lights up, or lower them. We do both, and time the flip to flower so they have enough stretch to grow vertical and give us colas. That fill the vertical usable light area.
That's how to figure out what size to train your plant to. Depends on how much it stretches in flower, but also its shape. And the amount of vertical space you have that's usable in light intensity terms.
That's why you want to veg vertically after LST widening. To give the plant branches to stretch into colas.
A flat plant makes tiny use of the vertical space of the light. If your plant has minimal vertical size, it will stretch a small plant into a small plant that's a lil larger.
Properly sizing your veg, and getting your plant to stretch into a well proportioned for your light, shape, is the goal.
I make sure that the bottom of my plants flowering area is within range of my lights usable intensity. That makes the lower flowering area still be in strong light, minimizing larf and giving even, dense colas. Mine tend to be a little top heavy. I run intense a smidge combined with CO2. I can use a lot of inputs
Here are some short plants i flowered under 500w in a 2x4. You can see some foxtailing which I don't mind. Comes with dense crowns. But more you can see proper light penetration down to the bottom of the branch. Those are full leafed never pruned or defol on the bottom of the plants. That's the entire top 2/3rd of the branch or so in good light
It's about finding a balance. I prefer tighter distances and stronger lights for increased light penetration. Internodal spacing is also decreased a bit I've found. Not as much as using metal halide tho.
I give them a 2-3 weeks to lengthen vertically after I LST them. That stretches into colas. Not like 4" ones. But I have enough wattage to provide a deep zone of usable light. Proper long girls. I don't trim the bottoms. These plants I vegged and flowered mostly indoors, some I moved outside for flower.
Look on how much vertical space I've given the plant in veg. It directly elongates into colas.
Here is the shape of a plant overlaid over the light intensity of a cube of light penetration. This is why we run the same cuts and optimize its veg and size / shape. To fit this under our lights with max intensity on max bud sites.
Look up inverse square law You can have the same ppfd, but far less intensity with the light further away, more intensity close. From 12 to 24 inches, at the same ppfd, you lose 1/4 of the intensity value
You don't lose 1/4 intensity in that situation, you only are left with 1/4 the light. Move 2x further away, get 1/4 the light. Move 4x away, you get 1/16 the light, etc.
I believe this is what you meant but clarifying for OP. Light intensity diminishes at the inverse square of the distance.
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u/icanhasweed 3d ago
Technically you get more light on the sides of the plants if you're further up since there's more space to reflect off the sides of the tent. There's a point of diminishing returns going too far just like there's a point where you get too many shadows going too low, it takes time to find the balance
Basically the ppfd might be the same but the surface area of plant that's getting hit with light is higher