Well that is not 'normal' you may have a weak ballast.
In general the T-8s will light right away but will take a few minutes to come to full intensity.
Same as any of the CFLs that have become so popular.
When you replace a typical 2 lamp 8' HO with a typical 4 lamp 8' T-8 you will have greater light output and the power consumption is less than 1/2 of the HOs.
A typical F96-T12/HO 2 lamp 120 ballast uses 237 watts and has a min start temp of -20F
2 lamp 8'Ballast A typical F32-T8 4 lamp 120 ballast uses 112 watts and has a min start temp of 0 F
4 lamp 4' ballast
