Lighting advice compact grow with limited headroom

[Caconym]

Hello! I am fairly new to growing, I have been involved with friends' grows but have only completed one tiny one of my own in a 90l bin under 2 65W CFLs. I have since progressed to a slightly larger space. I have a single plant growing currently, essentially as a test run. She's a few days away from harvest and I'm happy with her progress despite a few scary stem snapping hiccups.

I am looking for advice on what lighting option would be best suited to my (relatively unconventional) grow. Due to my living space being very small I am having to grow in a small box I have constructed with limited headroom. I have no space for a separate veg/mother/clone room. I plan to run a 12/12 from seed perpetual harvest cycle as this will enable me to keep the plants small and maintain a humble but steady supply.

The box has a 0.75x1m footprint and is 0.75m tall. I am currently running two 300W CFL bulbs and my maximum temperatures are starting to rise to around 31°C and although my test plant is happy enough so far I am concerned that with outside temperatures continuing to increase through summer I am going to run into problems sooner rather than later. I am running a 4" in-line fan and filter for extraction and a PC fan for intake. I cannot easily move more or cooler air through the box.

I have come to the conclusion that I need to reduce the wattage of my lighting to drop the temperature, however if I use a significantly lower wattage of CFLs my yield will be poor. I am considering switching to a 315W CMH bulb as this will solve the heat issue and also improve the light intensity and penetration. However with my limited headroom the plants will end up finishing very close to the bulb (probably about 4-6"). I have been researching the CMH bulbs and the consensus is that a greater distance (20-24") should be maintained to ensure canopy coverage and varying figures between 12-20" for minimum safe distance. I did however come across a couple of vague posts suggesting that plants had been grown very close to CMH bulbs with minimal negative effects.

Essentially what I would like to know is if I can get away with growing closer than the recommended distance if I maintain good airflow over the canopy with an oscillating fan and possibly use an air-cooled reflector hood. Does anyone have any experience with a similar situation?

Would a different lighting option be better?

I am aware that my grow space is not optimal but I am trying to do the best with what I have and willing to put work in to make it happen! I would love to have the luxury of a decent sized tent but that's a long way off for now.

 

[Caconym]

Not the best photo but hopefully it gives an idea of the space I'm working with.

 

[Giorkos1]

Take a look at my journal, it's a budget grow in a wardrobe but it performs really well
Pic from yesterday

Upgrading with LEDs is your best option to reduce temperature, but that's a problem for you I guess, you have a limited space(height)

 

[Caconym]

Hi Giorkos1, thanks for the reply. I had a peek at your setup and it looks awesome, you seem to be getting a lot out of your space to say it's 'just' a wardrobe. What's the closest your plants have been to the LEDs? Have you ever had bleaching?

 

[Giorkos1]

I started at 26 inches, and never moved it, the girls are growing just fine, no stretching no bleaching until now..
in case i notice a problem with the light distance i will move it of course

 

[Giorkos1]

Just to make it clear, i am not saying that the led sits at 26 inches now. I can tell you later when I go home if u wasn't

 

[Giorkos1]

Want*

 

[Caconym]

I would like to know if you don't mind checking. The maximum distance I can get between the lights and the canopy is about 20" at the seedling stage which would be fine but that will drop to about 6" when the plants finish.

 

[Giorkos1]

Will do when i go home,
This is what the manufacturer told me(mars hydro)

By the way, Information about how to grow with led grow lights, I believe these could do some help.

First:
Recommended light above plants for seeding,growth and flowering time:
Germination-------------24-30inches
Vegetable -- --------18-24 inches
Flower------12-18 inches

Second:
Recommended Lighting Time:
Vegetative Stage: 18-20 hours on,4-6hours off;
Flowering Stage: 12 hours on,12hours off.

Third:
Recommended Growing Conditions:
The rate of photosynthesis and transpiration are directly affected by temperature, humidity and airflow. Even though plants grow in many extreme environments, they thrive when given the perfect growing conditions. The perfect temperature and humidity for your plants are found between 75°-85°F and 50% - 70% humidity, with plenty of airflow to replenish CO2.

Notice:
The information above are summed up based on the data which given by customers actually planting.
Attention:
Keep appropriate distance of the light from the top of plants according to your real planting condition. If too close, might cause the plant leaf burn.
Using tips from our customers:
With more calcium and magnesium, and with ordinary clay would be better.

 

[Giorkos1]

The distance from the led is around 40-50cm.

Dimension of my wardrobe just in case u are interested, 150x50x75cm

 

[rhetorrikz]

I have a 800x800x1200mm veg cab and ive tried all sorts of lighting, i find @150+w temps will climb above ambient. im only using 120mm pc fans in and out with reduced voltage / voltage step for air exchange. To tell you the truth i have been using different lights at different stages of groth upping the wattage as the plants grow and using leds in summer t5's in winter and small single home made cree led cob (single) as an addition ..
With limited headroom you really need leds without focused lenses cobs may be a good option but depends on your outside ambient temps as to how much wattage you can run . Id be suprised if a 315w lec doesent heat that space up too much , but im keen to find out

 

[rhetorrikz]

 

[Caconym]

Hi rhetorrikz, I'm confident that switching to the 315 will drop my temps as I'm currently running 600W of CFL lighting. I will be looking into LEDs but the additional time and expense of researching and constructing an LED rig means I'm keeping that as a possible future upgrade.

I spoke at length with the chap in my grow shop yesterday and between us we reckon that as long as I keep the canopy swaying and good air exchange around the canopy I should be able to avoid any problems caused by proximity to the light. Will have to try it to find out, I'll update once I've got the light and put it in.

 

[rhetorrikz]

Out of interest , what are your average outside temps where you are ?

 

[Caconym]

Outdoor temps are 9-13°C during the night when my lights run, but my air circulates within my bedroom that sits between 18-22°C 24/7. I keep the window open to keep the room air fresh. My box hits a maximum of 33°C near the ceiling at the moment although in the middle of the space it's around 28°C.

 

[rhetorrikz]

Ok i have a bit warmer climate than you, my leds hum because of all the pc fans running which can be annoying , t5 is quiet , cobs with better heatsinks and lower voltage fans are good or your 315lec is cool with a good silenced extraction fan
I think at .75m tall 315 lec is too much tho

 

[Caconym]

Yeah I think the 315 will be pushing the boundaries a bit but it seems to be the best option at the moment. I will have a read up on LEDs though, these cobs keep popping up and I need to learn what they are and how they work!

 

[rhetorrikz]

Cobs are chip on board larger leds that you run from a driver like hids run off a ballest , good drivers can be dimmable too

 

[rhetorrikz]

They dont necessarily need lenses also which helps give a better footprint from a low height in your case .. and if paired with an efficient fan and heatsink they can run pretty quiet

 

[Caconym]

I've been having a read up and it's looking like 4 or 6 lower powered COB LEDs spaced across the box ceiling might be superior to the 315W CMH. Any thoughts on wattage?