Does anyone know what would happen? Does the ballast limit the power? If the T5 HO lamps were less expensive than T5 non-HO lamps, would it be ok to just use them in a non-HO luminaire?
The HO bulbs require more power output to operate than regular bulbs... and that is why there is an HO ballast, to provide that extra power. You could put a regular bulb in an HO fixture, but not vice versa.