Watts are a unit of Power. The lighting industry has a number of goals with regards to the design of light fixtures:
1) Improve color rendition
2) Extend lifespan in order to reduce replacement rates
3) Reduce the amount of power (Watts) needed to produce Lumens (visible light)
For the design team focusing on sustainability, light fixture placement and selection are primary strategies to improve the overall performance of the project. A high percentage of energy used in a building (especially commercial structures) and, to a lesser degree, homes is attributed to lighting. Lights use energy and also add heat to a space that must then be removed (cooled) by the air conditioning system–making the system work harder. Good design seeks to find the right balance between daylight harvesting and artificial lighting. Modeling the performance of a space or entire structure before construction assists the design team in optimizing the overall performance.