If you are trying for stealth then HPS is probably not the way to go.
You see with an HPS lighting system comes a ballast. Magnetic or Digital. Magnetic ballasts have quite a loud hummm. Not deafening or anything but certainly not stealth. Digital ballasts create alot less noise but cost alot more.
Then there is the cooltube to contemplate. IN order for a cooltube to be effective you have to use a Centrifugal inline fan which alone will cause around 30-60dB of noise thus stopping your stealth grow being stealth.
J