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I too had the 35C horror from my HPS, the worthless fans, the sleepness nights, 'til I discovered...PLEXIGLAS!

By inserting a wall-to-wall plexiglas shelf about 10cm beneath the lamp, that pretty much shuts the air below and the air above off from each other, with an exhaust fan leading a 9cm wide piping right under the lamp, and an in vent down by the plants, I reduced the heat by 8 degrees.
Google plexiglas + light transmission if you're worried about losing light, plexiglass allows around 97% through, even better than glass.

It saved my life, it may save yours!

I'd love to see your coffee can filter solution, it sounds doable!

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