Watts, lumens and lux: what are we comparing?
Separate electricity consumption, emitted light and light reaching the task.
Watts describe electrical input, lumens the light emitted, and lux the light arriving on a surface: 1 lx equals 1 lm/m². Lower wattage alone does not demonstrate equivalent lighting.
Luminaire output, distribution, mounting height and room surfaces all matter. Shelving needs vertical illumination; desks need light on the working plane. We compare the calculated lighting in the space and use total system power, including the driver, for the cost assessment.
Keep survey inputs separate: luminaire quantity, electrical power per complete luminaire and annual operating hours determine energy use. Lighting assessment needs output and optical data instead. If an existing fitting contains several lamps, do not count their quantity twice. Where system wattage is unknown, reliable documentation or professionally obtained measurements provide a better basis than estimating from the housing size.
What to clarify for your project
- Record total input power, including the driver or ballast.
- Compare complete-luminaire output and distribution.
- Calculate lux on the surfaces actually used.
Remember: Request total system wattage and photometric data for the complete luminaire.