Guide 06 / 10
Compare lamps that provide similar light
Use lumens for the light you need and watts for energy; watts alone are not a fair comparison.
Match the service
A lower-watt lamp is not necessarily suitable if it leaves the room too dim. Decide what light the space needs, then compare lumens, beam direction, and the same usage schedule. Watts describe input power; lumens describe visible light output. Also check color preference and socket compatibility.
Calculate the energy difference
Once two choices provide comparable light, subtract the new lamp's watts from the old lamp's watts. Multiply by hours per day, days, and the number of lamps, then divide by 1,000. The result estimates a kWh difference for your entered schedule, not a promised saving for every home.
Look beyond the bill
Purchase price, expected life, and switch compatibility also matter. If the existing lamp still works, you may start with the most frequently used rooms. Do not claim a payback period without real prices and usage hours.