LEDs have more than doubled in efficiency over the past 5 years, so even if sites have been converted, there remains scope for further savings. LED’s also get dimmer over their lifetime, and don’t catastrophically fail like traditional glass based light sources, even though the luminaires are still lit.

So it’s likely that after 5 years your installation could be operating way below current LED lighting efficiencies and a change could pay for it’self in less than 3 years.