DIY light reflectors

[hazymranch]

Does anyone have a good design/idea for DIY light reflectors?

I have a former industrial use hps light that has the lamp holder integrated into the ballast and it came with a round "helmet" kind of reflector designed to have the lamp hanging straight down.

I would like to turn this sideways and build a reflector to spread the light downward. Is something simple like a semicircle adequate? Do I need something like a 1/2 hexagon to focus the light?

Also, what materials are best? I have some mirror-finish stainless steel and a fair amount of mylar. Would mylar resist the heat apprpriately?

Cheers

[HydroACR]

semi-circle is probably plenty, I would just try and replicate an existing design.....