Hey all,

I returned home this week after a stint of working out of town and came back to some really cool new gear waiting for me, courtesy of Robin at Horticulture Lighting Group. There’s so much that I want to get done, but the first piece I was eager to experiment with was their Slate 3 Triple heat sink. You can check out my video review below, or continue reading and I’ll hit all the important points in text form for those of you who brought your phone to the bathroom and don’t want anyone to overhear you watching grow light videos while you’re in there.



  • The dimensions of the board are roughly 35″ x 7.75″.
  • Each Slate 3 Triple is pre-drilled for 3x QB288 or 3x QB304. Both boards are the same size and will fit the same holes.
  • Maximum power handling for this heat sink is rated at 320 watts. This means that if you’re running 3x QB288s, you can push about 2,000mA through each of them before exceeding the limit. If you’re running 3x QB304s, you can give them about 900-1000mA each. I was able to bump up to 2,100mA on my 3x QB288s without much of a temperature increase, but I’d recommend following the guideline of 320W.


If you only have 2 Quantum Boards and have an oddly-shaped grow space or are just looking for some more even coverage, you can run them on the outsides of a Slate 3 Triple to spread the light out a little. Performance is still decent in a 3×3, but I’d recommend going all out and using 3 boards for best 3×3 performance (we’ll get into some PPFD charts shortly!)

2x QB288s spread out on the edges of a Slate 3 Triple for better light spread.

A full heat sink.


I slapped some boards on the heat sink and started testing PPFD over a 3×3 space. The things I was most curious about were:

  • How much light do you gain by using 3 boards on a Slate 3 Triple vs. just 2 boards on the outer edges of the heat sink in a 3×3?
  • How does the intensity and coverage of a 2-board Slate 3 Triple stack up against a regular Slate 2 with 2 boards? (the black one that I built and tested in my last video)
  • What temperature can I expect at the heat sink and at the board when running at full power?

Slate 3 Triple: 3 Boards vs. 2 Boards

So, is it worth adding a third board and filling out the whole heat sink? Here are my results, measured at distances of 24″ and 18″ between the light and the quantum sensor. You can click on the images to make them bigger and easier to read:


Slate 2 vs. Slate 3 Triple with 2 Boards

This should be interesting, since both of these lights will use 2x QB288 Quantum Boards and will run at the exact same power, but the spacing between them will be different. The Slate 2 has the 2 boards pushed very close together, while the Slate 3 Triple has the large gap in the middle that’s intended for a third board:

A Slate 2 with 2x QB288

A Slate 3 Triple with 2x QB288

Here are my results at distances of 24″ and 18″ between the light and the quantum sensor for the Slate 2 vs. the Slate 3 Triple:


Heat Sink Temperature

As the boards warmed up, I took temperature readings up until temperatures stabilized, which occurred at about 35 minutes. Ambient room temperature was about 17 degrees Celcius. On the Slate 3 Triple with 3 boards running at full power (320W), I measured a maximum temperature of 71.5 degrees Celcius on top of the heat sink. I also took a measurement on the center of each QB288, and came up with a reading that was just a few degrees higher, at around 74-75 degrees. Repeating this experiment on the Slate 3 Triple with only 2x QB288s running yielded cooler readings in the mid to low 60s.


I think this form factor makes a lot of sense in a 3×2 or 3×3. The best configuration in my eyes is to use 3 boards on the heat sink and run it about 18″ from your canopy for a powerful PPFD of 800-900 umols/m2/s. These PPFD charts are also taken without any reflective material (they’re just open air measurements), so if you’re running this in a tent with reflective walls, you can count on even better readings around the perimeter of your 3×3. If you’ve got a pair of QBs and are moving up into a 3×3 from a 2×2, definitely check this thing out!

For more info, head over to www.horticulturelightinggroup.com or feel free to leave a question or comment below. Stay tuned for a whole bunch of testing coming soon with COBs and boards!