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White paint will give you good reflection. Mylar can be hard to work with, Reflectix is mylar sandwiched on bubble pad, tough and easy to handle.
Smithy with a 250 watt light you are only going to get 6"-8" penetration into your canopy and cover 24" x 30" (50 watts / square foot) - as you first suggested Low Stress Training will give you the best plant profile to get light to all light receptors. I have a simple lst method I call Crop Circle Of Bud on page 1 of the grow lab. Growing CCOB with a 250 watt light you could easily pull 250 grams after a grow or two, up to 500 grams with practice. If you'd like to go over starting CCOB please post in the Grow Lab thread so I can keep the FAQs together.
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