Grow Room PC Case Micro ScrOG - LED Based Nano Stealth Grow!

[thelastrebel]

Thanks for the info man - appreciate you taking the time. I was actually just wondering what you've found is the lowest current the series will operate properly with though. They're all measured at 350mA min but I'm interested in at what point you start to have colour shifting issues etc. I want to keep the output of each diode as low as I can basically but mid-power coloured diodes is a minefield.

What I would kind of like to do is repurpose my current driver (lpf-25d-36) to run two parallel strings at ~350mA each, but since that's bang on the rated minimum I'm not sure...

 

[icanelectoo]

Hmmmm, I haven't done a lot of research on other diodes. Maybe you could look into frosted lenses to increase the viewing angle? Is your main concern light burn?

My understanding of 'light burn' is that it's not actually a burn caused by excess light, but rather a nutrient burn caused by the excess uptake of nutrients due to excess light.
I might be wrong about that; but if I'm correct, then the light intensity doesn't matter, but rather the total amount of light the plant receives over short intervals of time.

Okay, so - If that's the case, rather worrying about driving your LEDs at a low current, you could drive the LEDs at max current, but reduce the duty cycle of the LED driver output from 100% to some lower percentage. This would simulate a lower current, but actually just cause the lights to flash (really, really, really fast). If you have the know-how, you can set up a circuit like this with a MOSFET (Source attached to the LED Driver GND, Gate supplied a PWM signal).

In my experience, working with digital electronics is way easier than analog systems - but this is, of course, assuming that I'm right about how nutrient burns work.
I'll try this in the future for sure and let y'all know!

 

[thelastrebel]

Hmmmm, I haven't done a lot of research on other diodes. Maybe you could look into frosted lenses to increase the viewing angle? Is your main concern light burn?

My understanding of 'light burn' is that it's not actually a burn caused by excess light, but rather a nutrient burn caused by the excess uptake of nutrients due to excess light.
I might be wrong about that; but if I'm correct, then the light intensity doesn't matter, but rather the total amount of light the plant receives over short intervals of time.

Okay, so - If that's the case, rather worrying about driving your LEDs at a low current, you could drive the LEDs at max current, but reduce the duty cycle of the LED driver output from 100% to some lower percentage. This would simulate a lower current, but actually just cause the lights to flash (really, really, really fast). If you have the know-how, you can set up a circuit like this with a MOSFET (Source attached to the LED Driver GND, Gate supplied a PWM signal).

In my experience, working with digital electronics is way easier than analog systems - but this is, of course, assuming that I'm right about how nutrient burns work.
I'll try this in the future for sure and let y'all know!

Yeah, basically I'm thinking about light burn and how to get the most spread and penetration possible. The literal temperature benefits of running diodes cooler is an added bonus but basically it's to minimise the hotspot light intensity, yeah. Optics are probably a good shout for these and the duty cycle 'dimming' is an interesting idea. Personally I probably couldn't be bothered having to work out and build the circuit but I'm sure it wouldn't exactly be difficult. Hmm. Not sure I've ever seen that done before - would be cool to know how it goes.

I think of light burn being due to water uptake not being able to keep up but I could be wrong on that. Either way I'm sure the effect isn't instantaneous enough to cause a problem with your idea. The only potential issue I see is if it would confuse the plant in the sense that it might keep trying to adjust for lights off - my gut feeling would be that process probably isn't fast enough to notice the flickering either but I'm no expert.

 

[icanelectoo]

Yeah, basically I'm thinking about light burn and how to get the most spread and penetration possible. The literal temperature benefits of running diodes cooler is an added bonus but basically it's to minimise the hotspot light intensity, yeah. Optics are probably a good shout for these and the duty cycle 'dimming' is an interesting idea. Personally I probably couldn't be bothered having to work out and build the circuit but I'm sure it wouldn't exactly be difficult. Hmm. Not sure I've ever seen that done before - would be cool to know how it goes.

I think of light burn being due to water uptake not being able to keep up but I could be wrong on that. Either way I'm sure the effect isn't instantaneous enough to cause a problem with your idea. The only potential issue I see is if it would confuse the plant in the sense that it might keep trying to adjust for lights off - my gut feeling would be that process probably isn't fast enough to notice the flickering either but I'm no expert.

I came across a study a little while ago that looked at the effectiveness of PWM controlled lighting on plants, it doesn't help with the nutrient burn problem, but I can also confirm that plants grow under PWM'd lighting

If anyone is interested:
https://www.sciencedirect.com/science/article/pii/S1011134411001096

Edit: Another benefit of running your LEDs at max current, is that LEDs are actually more efficient the closer to their maximum rating you drive them.

Edit [HASHTAG]#2[/HASHTAG]: I am actually wrong about Edit [HASHTAG]#1[/HASHTAG]

 

[thelastrebel]

I came across a study a little while ago that looked at the effectiveness of PWM controlled lighting on plants, it doesn't help with the nutrient burn problem, but I can also confirm that plants grow under PWM'd lighting

If anyone is interested:
https://www.sciencedirect.com/science/article/pii/S1011134411001096

Edit: Another benefit of running your LEDs at max current, is that LEDs are actually more efficient the closer to their maximum rating you drive them.

Interesting... it's been a long old while since I've looked at electrics in any great depth so I'm sure you'll know a lot better than me, but most of the product datasheets I've seen indicate a higher luminous efficacy at lower drive currents at a fixed temperature. Couple of variables there - in real world applications higher current will tend to result in higher temperatures (not so much on a reduced duty cycle though), making the diodes more efficient, and colour shifting could create a mismatch between luminous efficacy and electrical efficiency at different currents perhaps?

 

[icanelectoo]

My bad! I think you're right about this.
Unfortunately, it doesn't look like CREE added efficiency curves into their datasheet for the XP-E lights, but they did include these two curve sets. Looking at the Royal Blue diode, for example:

These curves show a forward voltage of about 3.1v for 350mA of drive current, and 3.3v for 700mA of drive current - (power dissipation over the junction of ~1.085W and ~2.31W, respectively), while the curve on the right has conveniently placed a relative radiant flux of 100% at 350mA, and 180% at 700mA. The LED consumes about 113% more power at 750mA, and actually only produces around 80% more radiant flux.

I thought I had looked at efficiency curves in the past showing a higher efficiency at higher drive currents, but the mind plays tricks

 

[icanelectoo]

STATUS UPDATE!

I'm back ladies and gentlemen, and I'm frankly a bit stunned by Rupert's growth - maybe I shouldn't be, you tell me.

I left three days ago and got back this morning. She grew slightly into the ScrOG net, so her new growth is a bit messy as it wasn't able to grow straight, but her top site is looking good (I think). If anybody has comments about the top site. please feel free to chime in!

I also noticed a smell in the room, even though this plant is still vegging. The problem was that I mistakenly selected a larger fan for the intake - making the growing environment a positive pressure system. I'm reversing the direction of the fan now and repairing the enclosure (I actually had to break the acrylic to switch the fan around, so it's a big job) I'll post some pictures now and some pictures later - when I'm finished and the growth has straightened out a bit!

For now, here's where we're at!

 

[MickJ]

STATUS UPDATE!

I'm back ladies and gentlemen, and I'm frankly a bit stunned by Rupert's growth - maybe I shouldn't be, you tell me.

I left three days ago and got back this morning. She grew slightly into the ScrOG net, so her new growth is a bit messy as it wasn't able to grow straight, but her top site is looking good (I think). If anybody has comments about the top site. please feel free to chime in!

I also noticed a smell in the room, even though this plant is still vegging. The problem was that I mistakenly selected a larger fan for the intake - making the growing environment a positive pressure system. I'm reversing the direction of the fan now and repairing the enclosure (I actually had to break the acrylic to switch the fan around, so it's a big job) I'll post some pictures now and some pictures later - when I'm finished and the growth has straightened out a bit!

For now, here's where we're at!
View attachment 954418 View attachment 954417 View attachment 954419

That light must be nice and bright, that girl is like ground cover. She also looks healthy .

Sent from my comfy chair.
[emoji16][emoji41] [emoji43][emoji848]

 

[thelastrebel]

STATUS UPDATE!

I'm back ladies and gentlemen, and I'm frankly a bit stunned by Rupert's growth - maybe I shouldn't be, you tell me.

I left three days ago and got back this morning. She grew slightly into the ScrOG net, so her new growth is a bit messy as it wasn't able to grow straight, but her top site is looking good (I think). If anybody has comments about the top site. please feel free to chime in!

I also noticed a smell in the room, even though this plant is still vegging. The problem was that I mistakenly selected a larger fan for the intake - making the growing environment a positive pressure system. I'm reversing the direction of the fan now and repairing the enclosure (I actually had to break the acrylic to switch the fan around, so it's a big job) I'll post some pictures now and some pictures later - when I'm finished and the growth has straightened out a bit!

Acrylic is a right pain to work with I found, I ended up constructing everything out of rubber sheet. What kind of filters are you using, they look quite low profile? I found when testing with candles etc that I needed 50mm carbon granules, but ymmv of course.

Plant is growing well mate, nice work.

 

[icanelectoo]

Acrylic is a right pain to work with I found, I ended up constructing everything out of rubber sheet. What kind of filters are you using, they look quite low profile? I found when testing with candles etc that I needed 50mm carbon granules, but ymmv of course.

Plant is growing well mate, nice work.

Thanks! Yes, In the future I'll be using acrylic only for the top, and I'll probably go with something like ABS for the sides - I just had a large sheet of acrylic lying around before I started this project.

I actually bought compost carbon filters for this system and cut them to size, I have no idea how well they'll work once I get this pressure issue fixed, but I'll be sure to keep everyone posted about that!