What is the difference between Volt Amps and Watts?

Watts and Volt-Amps are both measurements for electrical power consumption.

Watts (W) describes the energy consumption of a light, while volt amps (VA) refers to a lights potential power - because fixtures can potentially draw more power than their wattage rating, we use VA to calculate the capacity of your in-lite transformer. When calculating with VA, you can load your transformers to 100% capacity. However, if you are calculating with Watts you should not exceed 90% capacity of a transformer to account for additional potential power consumption.