Essentially, light power density (LPD) equates to all of the power consumed by light fixtures, ballasts, controls, transformers, etc., and is included in the watt measurement. If any other device or component is involved in lighting, then it must also be included in the calculation.
Several proposals are being considered to revise LPD so that it considers the length of time that a fixture is actually on and using energy. Designers also must factor in the effect that controls have on energy usage.