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It would seem we have Lumens and also Effective Lumens often stated as higher figure and RAW Lumens which is also higher measured before light reduction through glass and per LED x number rather then output as built.
Look at a MR16 spot lamp and typical 100 lumen per watt to 50 lumen per watt and automotive lamps have to be measured after they have warmed up but other lamps can be measured on switch on which will give higher output.
It would seem therefore as far as LED lamps go the lumen means very little so if lumen does not tell use real light output and watts don't tell us real light output how can we select lamps?
Look at a MR16 spot lamp and typical 100 lumen per watt to 50 lumen per watt and automotive lamps have to be measured after they have warmed up but other lamps can be measured on switch on which will give higher output.
It would seem therefore as far as LED lamps go the lumen means very little so if lumen does not tell use real light output and watts don't tell us real light output how can we select lamps?