I just use an Intermatic 60A rated time clock wired right onto my main panel with a dedicated 20A breaker running off it... very quick job for an electrician to install. I told him it was for electric baseboard heat to be installed in my attic.

Most HID bulbs you see in agriculture are 'horizontal burning', meaning they are designed to be burned sideways. If your bulb is 'vertical burning', it was designed to be run straight up and down, and should not be run on its side, which may shorten the life of the bulb.