For several months, I have been aware that there is analogy between numbers of lighting efficacy, expressed in lumens per watt, and automobile fuel economy, expressed in miles per gallon, MPG. Good state of the art in 2014 is a number of about fifty, for each. It seems we choose units such that common ratios come out at a "good" number of fifty. USA insulation measurement in R-value is another example involving ratios and inverse relationships, where more is good, to a practical limit. R50 is really good, and R100 is wasteful.
Current mediocre numbers are:
(These yet have virtue in that they can be improved with assured good investment.)
17 lumens per watt for a good incandescent light , and divide that by two or so, for inefficiency in shining wastefully like a point-source candle.
About 25 useful lumens per watt from the 50 lumens per watt of a common CFL point-source bulb. Again divide by about two for light upon a task vs. a directional light.
I ask this question at the Picasa Web Album supporting a recent blog post, Still Loving Glimpse Lights:
If I can still love Glimpse lights at crummy-old 50 lumens per watt, may I despise Cooper Wavestream SLD4 and SLD6 lights, of above 100 lumens per watt LED technology, but emitting only 52 lumens per watt?
Please study the above table with kind intent. We all know things must be set to a common basis for comparison. Brightness Numbers do this for task illumination. Imagine a standard house has fixtures distributed in ceilings where each holds a 100 watt incandescent bulb, and this is accepted adequate illumination. Each such light is B4. If a Sylvania 70732 that I call B8 is substituted for one bulb, it may be dimmed by half for same illumination; or if not dimmed, improved productivity and happiness need credit in the comparison, too.
Bottom-row numbers are with some improvement of Cooper SLD lights, to achieve about 100 lumens per watt. It might be the adding of a simple top-side reflector. Resulting added savings of electricity would be about fifty cents per year.
Have I been unkind to Cooper Lighting, in expressed dismay over their implementation of "Wavestream" edge-lighting as a planar luminaire? An SLD4 is a pretty light, if overly bright and large over a small hallway or a a shower. The unkind review needing improvement is here:
Should all who drive LED development beyond 50 lumens per watt, desist, working instead on simplicity and durability?