Originally posted by sonhouseWhat does that mean when a light bulb lasts 20,000 hours? Does every one of these last 20 k hour and then die? Is this guaranteed to do that?
I am going to buy some bulbs for our cleanroom, ... one lasts 20,000 hours, ... The other lasts 24,000 hours, called the super miser, consumes 30 watts ... If so, how much time is that?
Originally posted by FabianFnasNo, this is a real life problem. I am the maintenance department at Inplane Photonics, you can google them and see what we do.
What does that mean when a light bulb lasts 20,000 hours? Does every one of these last 20 k hour and then die? Is this guaranteed to do that?
In real life I think that 200 k hour mean that some will die quicker and some will last longer. Perhaps some will last only 1 hour and some other will last 100 k hours.
The question here is - does this remark ...[text shortened]... cal question with no bearing in real life and the answer is well defined until the last decimal?
Originally posted by aging blitzerInteresting point. The energy savings is about 6% so I would expect that to be the interest rate to equal the electrical differance.
get the cheaper ones, because in 20000 hours time (2+ years) the energy saving ones will be cheaper as they are produced more because of environmental concerns, and then switch to energy saving ones.
get the cheaper ones, and put the rest of the money into a savings account
(what is the minimum interest rate required to offset the extra energy cost?)
Originally posted by sonhouseLet's assume you need only one bulb (it makes no difference).
I am going to buy some bulbs for our cleanroom, 48 inch tubes, one lasts 20,000 hours, consumes 32 watts, costs $2.00 each.
The other lasts 24,000 hours, called the super miser, consumes 30 watts but costs three times as much, $6.00 each.
Power cost is $0.08 /Kwhr. If you have two cleanrooms with say, one hundred of these bulbs in each one, will there eve ...[text shortened]... come a time when the more expensive bulb will start saving money? If so, how much time is that?
Originally posted by aging blitzerMost of the time, 24/7 but lately we have decided to try to save some energy and shut down on weekends, sometimes overnight. So we are inconsistant with the power, that throws in another variable.
get the expensive ones if energy prices are going to increase
get some of each and check how long their average life really is
Are all the lights always on 24 hours a day, because if not, it takes longer for the energy savers to catch up.
Originally posted by David113Your work agree's with Xanth. So the bottom line is use the lower price ones unless you are General Electric, eh.
Let's assume you need only one bulb (it makes no difference).
If you use the cheap ones, then you initially spend 2 dollars, and then every hour you spend 0.00256 dollars for the electricity + 0.0001 dollars for new bulbs (since on average every hour you buy 1/20000 of a bulb). So after x hours you spend 2 + 0.00266x dollars.
If you use the expensive ...[text shortened]... money when 6 + 0.00265x < 2 + 0.00266x, that is, when x > 400000 (which is about 46 years
Originally posted by PBE6Well I mentioned that one set of very annoying lights. It turns out it wasn't even the friggin bulbs, but the ballast! How's that for irony.
You could also introduce an interest rate to take into account the time value of money. Assuming electricity is paid every hour, the cost for each bulb can be broken down as follows:
C(hardware) = B + B/(1+i)^p + B/(1+i)^2p + ...
C(electricity) = 1/(1+i)*(E + E/(1+i) + E/(1+i)^2 + ...)
C(total) = C(hard ...[text shortened]... less, the expensive bulb performed better, while above that the cheaper bulb was a better bet.