"Can I use a 1000watt lamp with 600 watt ballast?"
NO! You top-rated the specific wattage lamp to match the ballast. Although other wattage lamps may "operate" on other wattage ballasts, a non-matching ballast will either quickly bring on lamp to fail...
More
"Can I use a 1000watt lamp with 600 watt ballast?"
NO! You top-rated the specific wattage lamp to match the ballast. Although other wattage lamps may "operate" on other wattage ballasts, a non-matching ballast will either quickly bring on lamp to fail or produce only half the sunshine output the lamp was can really provide.
http://brugesinfo.net/buy-mushroom-grow-kits/
Less