Until yesterday, I haven’t needed to replace a light bulb in my house since I wrote the post with my analysis the cost efficiencies of LED vs. Incandescent bulbs.  Historically though I’ve tended to purchase CFL whenever possible, more because I’m the sort of guy who forgets to replace one light bulb in the room until both blow out.  Thus, due to the longer service times of CFLs, I am left in the dark much less frequently.

This time though, I figured I would look at the LED options.  As I hunted around, the one that particularly caught my eye was the fact that some manufacturers are now making LEDs into candelabra shapes.  As I like to leave the lamp outside the house on during all night time hours, this is probably my most irresponsible use of electricity at being turned on 12 hours a day on average.  The lamp I currently have does have a dimmer that kicks it into high gear when motion is sensed, but I need to replace the light because that motion sensor/dimmer timer thing is broken.  It’s spotty at best and regardless of what duration the lamp is set at, it only turns it on bright for about 15 to 30 seconds,.  Not to mention those bulbs are burning out all the time.

Unfortunately, I forgot to bring the spreadsheet attached to my previous post to my favorite (read favorite as most conveniently located) big box retailer with the biggest selection of light bulbs.  Therefore, I went home (wondering how much the two trips is costing me in gas and chiding myself for not planning ahead) and started doing some math.  I estimate that at 365 hours per month, at $0.11 per KWH, the outside light costs me about $58 per year.  I know it is less than that because it dims, but I don’t know how much wattage it uses when dimmed, so I’m starting with the worst case scenario.

And then I saw this as I compared the LED candelabras to the incandescent I currently use:

 

25w

40w

2.5w LED

3w LED

Light Output (lumens)

300 lm

540 lm

30 lm

30 lm

 

                Hrmm…  Cut my light output by a factor of 10 by cutting my wattage by a factor of 10.  Great for cost efficiency, but that pretty much defeats the purpose of why I have the lights out there.

                Apparently it was “Time to change the paradigm”, as we like to say in the corporate world when we think marginally outside the box.  So I fundamentally re-evaluated how I was looking at this problem.  Since I was using 3 bulbs at about 540 lumens each, I decided my goal should be to see how to produce about 1600 lumens as cheaply as possible.  After a little research, I found that this was the amount of light output by a 100W bulb.  Note, a lot of 100W bulbs do less than this, so I had to hunt around to find one that did, but that came at the expense of a shorter service life.

 

                Now that I had the information I needed to compare between bulbs, it is all about plugging in numbers to the spreadsheet.  Here are the important details:

·         Incandescent - $0.97, 100W, Estimated Service Time 750 hours

·         Current Candelabra - $2.47 (3 bulbs), 120W, 150 hours

·         CFL (Dimmable) - $8.97, 23W, 10,000 hours
Assumption:  Dimmed = ~12W, and as an exterior light it will be mostly dimmed.

·         CFL (Non-Dimmable) = $1.99, 23W, 10,000 hours

·         Assume cost of capital is 0% and cost per KWH = $0.11

 

                Plugging all the data into the spreadsheet I came to the following conclusions:

·         Non-Dimmable CFL (payback at end of life of the first bulb)

o   Compared to 100W Incandescent - Break Even – 0.02 years (7.3 days) and saves $73 over the cost of the almost 2 years the bulb should last.

o   Compared to the candelabra, immediate (heck the CFL bulb is cheaper) and saves $94 over the 2 years of the bulb.

·         Dimmable CFL (payback at end of life of the first bulb)

o   At 23 watts for 12 hours a day

§  Compared to 100W Incandescent – 0.19 years (69 days), $66 in savings

§  Compared to candelabra, 0.12 years (43 days), $87 in savings

o   At 12 watts for 12 hours a day

§  Compared to 100W Incandescent – 0.17 years, $75 in savings

§  Compared to candelabra – 0.11 years, $96 in savings

The conclusion becomes, in order to maintain the same amount of light I should replace the lamp with one that will take a CFL.  Over the long run, the dimmable CFL does pay off, but to the tune of $9 every approximately 2 years.  Since I get more light (lumens) out of the non-dimmable (1600 lumens) vs. the dimmable (1400 lumens) I will need to figure out whether the $9 a year saved is worth the reduced amount of light or I need to find a light where the “2-Level Lighting” feature can be disabled so that I can maximize my flexibility in selection of bulbs.  In reality it isn't all that significant dollar value in payback though the savings relative to the spend are awesome, but at least I don't feel so bad replacing my currently broken lamp as I know I'll make it back in 2 years.

Thanks to the massive savings predicted by my analysis, this gives me a little freedom to invest in researching the various solutions available.  As I think back to my scientific method and designing experiments to test my hypothesis that I need 1600 lumens to adequately light the area, several historical examples come to mind.  As such I have chosen to leverage one of the best historical examples of decision making by process of elimination.  In this regard, I will follow the wisdom of the Goldilocks.  I will try both the dimmable CFL and the non-dimmable until I find one that is “just right” (see references at the end for the complete history of her experimental work).

References:  Dramatic Reader for Lower Grades by Florence Holbrook - Project Gutenberg