This post is aimed at family which recently let me install fourteen Sylvania 70732 LED Disk Lights, $35 each on sale and emptying the inventories of two Lowe's stores in Denver. $490 there. I also spent $100 for involved dimmers, needed where before darkness was suffered. Now there is light to spare sometimes. I told these "investors" they would get their money back in a year. Showing this is not simple. It's a lot of money. I couldn't show them supporting argument from powers that be. A 7.5% sales tax added to the cost. A needless luxury? Denver, like Portland, still offers no rebates for residential LED lighting. No one cares what you do, or how you do it.
Before getting to the math, create a summary of involved Brightness Numbers. Our needs are for useful task illumination, whether just reading a book, keeping out of danger, or guiding a tool. Light intensity upon a task is not measured in lumens. A Brightness Number with standard definition yet to be established, expresses the task light intensity, integrated lumens in a unit work space. I define B4 as the useful task illumination from a 100 watt point-source bulb, and find that fully-presented directional light from a 4" Glimpse light, 300°K, 450 lumens, is matched to the task illumination of assorted "100 watt" point-source bulbs. The Brightness Number for any other fully-presented LED light will be proportional to its measured lumens, whatever the task and location/ size definitions.
We must become fully aware of a roughly times two advantage that directional light has, in illuminating a task, vs. that old point-source candle. We used point-source light, only when that was all we had. Down lights were a step in the direction of lighting efficiency, if point light really received concentration in a well-directed reflector. The ideal light now is in the natural directionality of a glowing plate, usually left to just beam away without guidance.
Times-two efficiency vs. point sources is yet to be emphasized in product marketing, but I have one public acknowledgement to share. I think a number like this is inferred in "efficiency" numbers, at page 3 in this Lithonia document. The Lithonia numbers acknowledge that CFL point sources are inferior to incandescent, CFLs beaming very little where needed.
Brightness Numbers appear in the following table of information and math operations.
I replaced a mix of bulbs in the fourteen can lights, mostly foolishly-employed CFL bulbs shining out very little of their light. The change of house cheerfulness is dramatic, especially in bathrooms.
Differences in the column, Savings vs. Reference are directly usable to infer time until investment is recovered. Forget the dimmers investment for now and think only of the bulbs hauled out. Each Sylvania plate LED will save at least $150 in 35,000 hours, more than was saved by just moving on from incandescent bulbs. How long does it take to save just the $35 luminaire cost? Not more than about 8000 hours. That's 2.7 years at 8 hours per day. Some lights will run eight hours a day. Payback time isn't the year I had promised. Maybe I said two years? There were incandescent bulbs replaced. Payback for them, is in less than a year, if operated five hours a day.
In hours, Payback in replacement of any incandescent bulb with the Sylvania luminaire is as:
Payback/35,000 = 19/396. Payback = 1679 hours
If used five hours per day, Payback = 0.9 year.
Whatever, and if someone can offer helpful correction of my thinking, payback is better than anyone should expect from money in any other investment, including almost all other forms of "weatherization."
Money back on the dimmers? If a dimmer works only one light, longer payback of the larger investment will bother.
Oh, about that Costco Luminus LED light at bottom in the table? It's OK. Lots of brightness probably to be dimmed. Same savings. Same 65 lumens per watt technology as the Sylvania 70732. Tight against the ceiling it may be a better block of a leaky can light than the Sylvania 70732. I think the can retrofit is easier with the Sylvania 70732, which does not demand that the can have clips to engage springs. I still want to eliminate attic floor cans, know how to do so in all cases, and want to replace cans with junction boxes. I hope the Costco offering doesn't encourage anyone to newly install a light can. Use a junction box!
Please see all posts on blog subject LED Plate Lights.
Early Adoption Is Good:
At 7/29/2014, add comment on "early adoption." You will not save money by waiting for an improved version of an acceptable product. I have customers still happy with Version One of Sylvania 70732 lights and with 6" Glimpse , both now superseded by better lights. Where a customer is not happy with imperfect dimming or with the mild buzzing of Glimpse lights, I will take them back, credit half the material cost I and they paid, install the improved light at my cost of the light, and will give the returned light with disclosure to another customer.This is good for everyone. I hope other installers will follow my example.
I will not give the less-perfect light to charity, where the deficiency would not be disclosed. I imagine efficient-lighting informed charities, where I might donate even live CFL bulbs and fixtures now unwanted. Where a light might last forever, individuals too will look for means to move on to new products.
Know that where an energy-saving investment survives for twenty years, or sixty, there are important returns because energy costs grow much faster than inflation. Please help me to imagine the more-complete payback math where there is accounting of inflation and present value in energy conservation, of a perpetual return on investment, Perpetuity Math .