Physics question on light bulbs!!!?

Question

Energy experts tell us to replace regular incandescent lightbulbs with compact fluorescent bulbs, but it seems hard to justify spending $15 on a lightbulb. A 60 W incandescent bulb costs 50 cents and has a lifetime of 1000 hours. A 15 W compact fluorescent bulb produces the same amount of light as a 60 W incandescent bulb and is intended as a replacement. It costs $15 and has a lifetime of 10,000 hours. Compare the life-cycle costs of 60 W incandescent bulb to 15 W compact fluorescent bulbs. The life-cycle cost of an object is the cost of purchasing it plus the cost of fueling and maintaining it over its useful life. Which is the cheaper source of light and which the more expensive? Assume electricity costs $0.10/kWh. Be sure to compare the two over equal time spans.

Answer 1

First, find out how much energy the incandescent bulbs use:

(60 watts) x (1000 hours) = (60,000 watt hours)

60,000 watt hours (Wh) = 60 kilowatt hours (kWh)

Now, figure how much it costs for the energy. You know how many hours the bulb runs, and you know the cost per hour, so...

(60 kWh) x ($0.10/kWh) = ($6.00)

However, you need to add the cost of the bulb, since it doesn't just appear out of nowhere. You DO have to buy them.

$6.00 + $0.50 = $6.50

So, every incandescent bulb costs $6.50 per 1000 hours, energy included.

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Now, you need to do the same thing for the fluorescent bulbs. Calculate the amount of energy consumed by these bulbs.

(15 watts) x (10,000 hours) = (150,000 watt hours)

150,000 watt hours (Wh) = 150 kilowatt hours (kWh)

Once again, it's time to figure how much it costs for the energy. You know how many hours the bulb runs, and you know the cost per hour, so...

(150 kWh) x ($0.10/kWh) = ($15.00)

Once again, add the price of the bulb into the total cost.

$15.00 + $15.00 = $30.00

So, over the course of 10,000 hours, the total cost of the fluorescent bulb is $30.00.

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Now, time to add up all of the total costs. First, compare the two bulb prices.

Incandescent: $6.50/1,000 hours
Fluorescent: $30.00/10,000 hours

At first glance, it appears as if the Incandescent bulb is much cheaper. However, you need to convert the incandescent into the same time frame as the fluorescent. The incandescent costs $6.50 per 1000 hours. But, you need 10 incandescents to match the time frame of the flourescent. So:

($6.50 per 1,000 hours) x (10) = ($65.00 per 10,000 hours)

Now, compare the costs.

Incandescent: $65.00/10,000 hours
Fluorescent: $30.00/10,000 hours

Over the course of 10,000 hours, it is clear that the fluorescent is the cheaper of the two. By purchasing fluorescent bulbs, you are saving 35 dollars, or 46.2%, with every bulb.

Hope that helps!

Answer 2

errr.. if the compact fluorescent bulb costs $15 and the incandescent bulb costs 50 cents.. The fluorescent light bulb costs 30 times as much, lasts 10 times as long and consume 4 times less energy per unit time. In short fluorescent is cheaper.

Answer 3

You have the problem correctly set up, and the solution is straightforward. But CFL's these days do not cost anywhere near fifteen bucks a pop; you can buy a pack of six of the things at Home Depot for less than ten bucks. So, the per-bulb cost is $1.66, and that makes the swap much more feasible. Also, ten cents a kWh is fairly cheap these days; in most areas, the cost is more.

Answer 4

If you look at the problem a different way and consider the savings in energy consumption nationwide. The use of fluorescent bulbs provides a huge benefit to us all. In the long run there is much less demand for fossil fuels. Thus, we would all save tons on money and help the environment at the same time.
It is typical for people to think only about thier own savings and not of the benefit of everybody. It is human nature and it stinks.

Answer 5

Ok, let's compare:

Incandescent starting cost: $.50
Watt output: 60W

kWh output in 1000 hours: 60 kWh

Cost of electricity for 1000 hours: $6.00
" " for 10,000 hours: $60.00

Life-cycle cost for 1000 hours: $6.50
" " for 10,000 hours (assuming 10 bulbs were bought): $65.00

Compact Fluorescent starting cost: $15
Watt output: 15 W

kWh output for 10,000 hours: 150 kWh
" " for 1,000 hours: 15 kWh

Life-cycle costs for 10,000 hours: $30.00
" " for 1,000 hours: $16.50

If you were only going to use the compact fluorescent for only 1,000 hours, your best bet would be incandescent, but over 10,000 hours, one compact fluorescent outlasts ten incandescent ones and is half the overall cost.

Answer 6

This is really rather easy to prove:

Purch. Then 1000 hrs
Bulb- - -Power Cost
0.50-----6.00 total cost 6.50
15.00---1.50 total cost 16.50

at 2000 hrs (incandescent bulb replaced)
0.50-----6.00 total cost 13.00
zero -----1.50 total cost 18.00

at 3000 hrs (incandescent bulb replaced)
0.50-----6.00 total cost 19.50
zero-----1.50 total cost 19.50

Notice that the fluorescent job lasts for 10,000 hrs so no
replacement bulb is needed. you break even at the end of
3000 hours usage. From 3000 hours on up to the expected
10,000 hour life your fluorescent bulb is saving you money.

For example, you save 26.00 minus 21.00 = $ 5.00 per bulb converted at 4000 hours.and at 5000 hours you have saved
32.50 minus 22.50 = $ 10.00 per bulb converted, etc. etc.

Answer 7

One thing I have seen based on the CFLs I've bought - they dont last anywhere close to what they're advertised to. And who can keep receipts and keep track of how long something has been used to try to get a refund?

Answer 8

The 40 watt's filament supplies greater resistance to the means. The resistance of the 60 watt filament is below that of the 40 watt, to that end permitting greater present day (amperes) to bypass to that end becoming (changing electrical energy) to mild.