One last thing to keep in mind BigBudBalls in terms of heat, keep in mind that mylar has a broad band reflectivity that extands out to far-IR which would be lower temperature heat. It's likely the case that mylar is going to reflect more heat than white paint. A HPS light as a black body radiation source does not give off much mid-IR, it does give off a lot of far-IR.

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Talk, without the empiricism to back up your statements, is dogmatic BS.