Linear Fluorescent lighting energy efficiency is based on the lamp/ballast system. Typical configurations include:

T12 system (T12 bulb + magnetic ballast) = lowest efficiency
Standard T8 system (T8 bulb + electronic ballast) = higher efficiency
Advanced T8 system = highest efficiency

Retrofit Energy Savings Estimates:

From T12 system to Standard T8 system - 25% energy savings
From T12 system to Advanced T8 system - 43% energy savings
From Standard T8 system to Advanced T8 system - 12% energy savings