In a previous post, I built a pair of space buckets to start my 3000K and 5000K peppers in. The buckets worked excellently – they made it really easy to control temperature, humidity and airflow, and they got my peppers off to a great start. One of the best features of the buckets was how much light made it from the COB down to the plant canopy – especially after the walls were painted white. Off of a single Vero 18 COB, at the very bottom of the bucket I was getting a PPFD of 500 µMol/m2/S and at 12″ away from the COB, I was getting 1,100 µMol/m2/S. Having seen how well these worked, earlier this week, I set out to test out another popular “Space” device: the mighty Space Tote. For reference, here’s spacebuckets.com’s prime example of a space tote build that actually looks nice!

Experiment Goals

I aimed to accomplish 2 things with this build:

  1. Figure out how many COBs a Space Tote should have for optimal PPFD levels.
  2. Determine how much of a difference reflective walls makes on PPFD.

Parts

The parts I used for this test are as follows:

  • For the Single COB Version
    • 1x Cree CXB3590 3500K COB
    • 1x Mean Well LPC-60-1400 1,400mA Driver
  • For the Double COB Version
    • 2x Cree CXB3590 3500K COBs
    • 1x Mean Well HLG-185H-C1400B 1,400mA Driver (both COBs running at 1,400mA)
  • For the Reflective Material Tests
  • For PPFD Measurement
    • Apogee SQ-500 Quantum Meter with Extech Multimeter

Assembling the Space Tote

Since I don’t intend to grow anything in here and was strictly doing this to examine PPFD, I didn’t cut in any access hatches or holes for fans. I was only concerned about getting light into the totes and measuring it. Don’t judge me for the very “temporary” look of this thing! It’s not my best work, but, sadly, not my worst either.

The classic Space Tote is built with two 20 gallon totes: one right side up, and the other stacked upside-down on top. Normally, the totes would be fastened together somehow to prevent the top one from sliding around and falling off. I just lined them up and left it loose.

Space tote 20 gallon totes

I used 2 different types of totes for this build. The bottom is a Rubbermaid Roughneck 18 gallon tote, the top is a Centrex 18 gallon “Rugged Tote”. The build quality difference becomes very apparent when they’re lit up.

Now, I hope you’re still with me after that rigorous assembly phase. To recap, so far we have performed the following steps: 1- Turn one tote upside-down and put it on top of the other. Take a breather! From this point, I just needed to cut in a hole for the single COB experiment, and then cut another 2 holes afterwards for the double COB variation, and seal the original one.

Single COB Tote

All I did to set this up was cut a hole in the middle of the top tote and use aluminum tape to seal around the COB. I used the tape on the top side and on the bottom as well, to ensure a good seal.

Tape on the top side to seal the COB in.

With no reflective material, the difference in how light-proof the 2 different brands are is huge. The top is the Centrex tote, the bottom is the Rubbermaid.

Double COB Tote

For the double COB tote, I sealed the center hole I had originally cut with aluminum tape, and cut 2 new holes to accommodate the 2 heat sinks.

The double COB tote shown with reflective material. This thing looks hilarious but it worked!

Inside the double COB tote with reflective material in place.

 

Adding Reflective Material

I took PPFD measurements of the single and double COB setups, with reflective material and without. I taped white poly to the walls of the tote for a quick test, but I would recommend spray-painting the walls with a flat white paint for a permanent install. I did my best to smooth out the poly along the walls.

PPFD Results

The total height from top to bottom of the 2 totes is 32″. I measured PPFD  with the sensor at 3 heights in the tote:

  • The bottom surface of the tote.
  • 12″ up from the bottom (20″ below the COB).
  • 24″ up from the bottom (8″ below the COB).

 

Bottom

12″ off bottom

24″ off bottom

Reflective bottom

Reflective 12″ off bottom

Reflective 24″ off bottom

Single COB PPFD with no Reflective Material

  • Bottom of tote = 70 µMol/m2/S
  • 12″ off bottom (20″ below COB) = 150 µMol/m2/S
  • 24″ off bottom (8″ below COB) = 560 µMol/m2/S

Single COB PPFD with Reflective Material

  • Bottom of tote = 260 µMol/m2/S
  • 12″ off bottom (20″ below COB) = 440 µMol/m2/S
  • 24″ off bottom (8″ below COB) = 870 µMol/m2/S

Double COB PPFD with no Reflective Material

  • Bottom of tote = 140 µMol/m2/S
  • 12″ off bottom (20″ below COBs) = 280 µMol/m2/S
  • 24″ off bottom (8″ below COBs) = 880 µMol/m2/S

Double COB PPFD with Reflective Material

  • Bottom of tote = 500 µMol/m2/S
  • 12″ off bottom (20″ below COBs) = 720 µMol/m2/S
  • 24″ off bottom (8″ below COBs) = 1,440 µMol/m2/S

Conclusions

I was surprised to see how big a difference the reflective material made. If you’re not making your walls reflective, you could be losing 50% of your light by the time it hits your plants. As mentioned above, I would recommend painting your tote walls with a few coats of matte white in order for a cleaner install.

You might be able to get away with a single COB in a tote, but 2 are definitely optimal. I took a few measurements off in the corners of the totes, and with the single COB, PPFD dropped off about twice as much as the double COBs. With 2 COBs and reflective material, I was getting 500 µMol/m2/S on the bottom in the center, and 470 µMol/m2/S on the bottom, tucked right into the corner. Not bad! That being said, I’m running these CXBs a little higher than 50% of their max, so you might be able to get away with sufficient single COB PPFD if you ran it harder, but 2 would be best.

These results will be applicable to most popular 36V COBs on the market, give or take a few µMol/m2/S.  If you’re using Citizen V6 CLU048-1212s, or Gen.7/SE Vero 29s, you can expect very similar results.

Curious about PPFD for any other “Space” containers? Let me know in the comments and I’ll try to test it for you! Also, check out the DIY Guides section for more info on growing with COB LEDs.