I found some fluorescent bulbs that have these specs:
14w (“replaces 60w”), 900 lumens, life 10,000 hr, cost $1.66
I plan to replace the current bulbs which were:
60w, 900 lumens, life 1,500 hr, cost $0.25
I pay 10¢/kwhr
Clearly the fluorescents will save over the long run, but I’m not sure at what point the power savings overtakes the initial cost.
So, the question is - Does it make sense to change out good bulbs immediately, or should I just replace them as they burn out?
If I replace them immediately, should I save the ½-used bulbs or throw them out?
For simplicity, I suppose we could just say the existing bulbs (being on average half used up) are the same as new bulbs which have a life of 750 hr and costing $.0125
Actually, I guess what I want to know is when is that crossover point, how many hours?
In terms of the break-even point, that’s pretty simple, i.e., how much usage after purchase will the higher initial cost of the fluorescent be offset by its lower energy consumption. Let this time be x, measured in thousands of hours. You just have to solve the straight-forward equation: 1.66 + .10(14x) = .25 + .10(60x). The answer is x=.3065. So it’s a little over 306 hours. If the cost per kwhr is c, the answer is .03065/c thousand hours.
Another way to look at it is to figure the cost of leaving the old bulb until it burns out.
To start with, I would entirely discount the remaining “value” of the existing bulbs. They’re already paid for; it doesn’t cost you $0.125 to just leave them there (I’m assuming they have no resale value to speak of). So your cost to leave them there for the next 750 hours would just be the cost of the electricity they use. At $0.10/kwh, its costing you $0.006 per hour, x 750 hrs = $4.50.
For the fluorescent bulbs, the same 750 hours costs $0.0014 x 750 = $1.05; plus the $1.66 purchase price = $2.71. So it costs you $1.79 to leave a bulb in until it burns out.
Personally, I save the old ones for use in fixtures/locations where fluorescent doesn’t work well.
Average cost of running energy savers for t
14t(.0001) + 1.66t/10000 = 0.0014t + 0.0000166t = 0.0014166t
Average cost of running normal bulbs for t
60t(.0001) + 0.25t/1500 = 0.006t + 0.000166t = 0.006166t
Assuming current bulb has life of 750h left
0.006166(750) = $4.6245 cost of running current bulb
0.0014166(750) + 1.66 + (750/10000)1.66 = $2.86695 cost of running energy savers + new bulb + depreciation of new bulb for 750h
I use compact flourescent bulbs wherever I can, even though it causes just a tad of tension in the house because my wife doesn’t like them.
However I’ve found that the claimed 10000 hour life is largely mythical. Maybe under ideal conditions with the base of the bulb maintained constant at 20 C they would get that kind of life. That’s a little over 2 years approximately assuming that it’s dark half the time and the light is on whenever it is dark… In the fixtures around my house under actual operating conditions they don’t do that well.
0.006(750) = $4.5 cost of running current bulb
0.0014(750) + 1.66 + (750/10000)1.66 = $2.8345 cost of running energy savers + new bulb + depreciation of new bulb for 750h
Savings for changing the bulb now and throwing the old one away = $1.6655
There you go. Whew.
I started replacing the bulbs in my house with the compact fluorescents about 3 years ago. Before that, I was replacing each bulb about once every 2 months. I’ve never had to replace a compact flurorescent. Each one I’ve installed is still working. Even at the $7.00 they cost when they first came out, I’ve still saved money.
If only I could find a compact fluorescent ‘bug bulb’ for my porch light, things would be perfect. My porch light burns out every 2 or 3 weeks, probably from the door being opened and closed causing vibrations.
Thanks for the math, people!
Looks like I can just replace them all in one swoop and toss the oldies without regrets.
That’s what I prefer for another reason - adding in for my own time. One trip around and the chore’s all done for many months.
I understand at big companies, with seas of overhead lights, that they always prefer to replace them all at once rather than have continual dark spots and maintenance calls.
jasonh300 -
Sounds like what you need is a yellow cover for your white light. If they don’t make such a thing, maybe you can invent it and get royalties!
The general ‘wisdom’ is replace them as the old bulbs burn out. Also you may wish to place them in areas where their drawbacks are least noticable.
Some drawbacks I have noticed are:
#1 is they don’t start instantly, though I have a few that do, most take a second to light, which can seem like a very long time.
They don’t develope full brightness till they are on for a few minutes.
They don’t work (well) on dimmers or motion sensors.
Some notice flicker
The equivalant wattage seems overrated, and a CF that says it’s about as bright as a 75 w bulb, is (IMHO) about as bright as a 60W bulb.
they don’t do well in low temps.
Actually this should be your biggest reason - if you wife has trouble with them, it ain’t worth it, spend the extra $$$$ over the lifetime you have together to help her live in a happy environment.
but if you are going to put them in, I would say put them in in places where instant light in not needed, and the lights, when turned on, will be on for a long time.
They have such a thing…You can buy them in different colors and it’s done with a plastic coating on the lightbulb. But I’m not sure if it’s a specific color in the spectrum of yellow that keeps the bugs away.
I bought yellow floodlights for the backyard and they seem to do well with the bugs. Maybe I could buy the colored ones and see if they work…or even spraypaint them.
Actually, over the last 60 years we have come to a quite sensible accomodation. I tolerate the trifles that irritate me and she tolerates the trifles that irritate her.
Oh they do make a yellow one for a ‘bug’ light, and I have it in my porch light. I don’t think it works as well as a standard bug light, maybe becasue CF do product more UV light which IIRC attracts bugs.
Hmm. My physics teacher sense is tingling at this. We just looked at the spectrum of CF -vs- incandescent lights in class last week, and one of the problems with CFs is that they produce a higher percentage of blues than yellows/greens. This gives them that blueish tint (as compared to the incandescent bulbs). This also means that putting a yellow filter over them is going to make them much darker, necessitating a much brighter CF to light up the room.
Personally, I hate CFs, and I think they are much less warm (in the non-physical sense as well as the physical). I’ve also always wondered about whether humans can perceive the 60Hz flicker in some way that makes us uptight. (while the incandescent bulbs also run on the 60hz current, they don’t have time to dim during the cycle, so they stay just as bright).
I know we’re straying out of GQ into IMHO here, but I have to agree. I cannot stand fluorescents of any shape or form. Their cool color cast bothers me and somehow they do make me feel uptight. I’ve worked in offices with flurorescent lighting and offices with incandescent lighting, and I have to say I’ve always felt much more at ease and in a better mood around incandescent lighting.
I’m wondering about the folks who need to change bulbs all the time. I have a big place with 135 incandescent bulbs in various fixtures, plus 10 4’ flourescents in utility areas & 8 12" mini flourescents as under/over cabinet lighting. yes, I just went and counted them all.
I use the typical mid-grade 75, 100, & 3-way 50-100-150W incandescents I get from the big box home center. And loss-leader shop-grade flourescent tubes. Nothing fancy anywhere.
I change one bulb maaybe every 3 months.
If I had a fixture that needed a new bulb within 2 years of the last one, I’d be all over it with a meter trying to figure out what’s wrong with the wiring.
What am I doing right or wrong? How can people (or their lamps) eat lightbulbs like candy?
The light output of a fluorescent tube declines 20-30% over its life, so you may want to replace all of the tubes on a fixed schedule to save time and maintain efficiency.
