Calculating energy costs.?

03-18-2009, 04:41 PM

I'm not real big on the whole a train left going this way at 60 mph and another left going 30mph when will they meet either BUT look at this:

LED 5watts X 12hours = 60 watts a day which is 0.06KW x 100 days of use = 6kw X 13 cents your cost per kw = 78cents for 100 days electricity

Incandescent 60watts X 12 hours =720 watts a day which is 0.720KW x 100 days 72kw x 13 cents = $9.36 for 100 days electricity

In short Incandescent every 100 days costs $9.36
LED $0.78

For a savings of $8.58 every 100 days

Throw in the fact that the LED's last longer by far and it is about the biggest no brainer around you can't afford not to spend the extra money and get the LED.

Ok did a little more math looks like around day 117 the LED pays for it's self and starts saving you a little less than 9 cents every day after that.

Point taken from fancy if you take the $10 difference and invest it in a cd for those 117 days I guess it might take the LED until day 120 before it starts paying (Figure $10 at a hard to get 8% invested for all of 117 days you get around a quarter in divedends at a bit over 8 cents a day that gets you 3 days) I'm done

03-18-2009, 04:41 PM

Long question, I'll try to make it short.

Costco sells these LED flood light bulbs that use 5 watts of electricity, but give off the equivalent of a 60 watt bulb. The LED bulb costs $15.00 (total including tax) while a old fashioned incandescent flood light bulb costs $5.00 (also total price including tax)

The LED flood light bulb claims to last 10 times the life of the incandescent bulb. And electricity rates are about 13 cents a kilowatt hour where I live.

How long will it take for the LED light bulb to pay for itseff if used 12 hour a night Say from 7.00 PM to 7.00 AM

electric costs 13 cents KWH, LED energy usage 5W VS. Incandescent 60W

Thanks. I really suck at math. Is it worth it to get many of those expensive LED bulbs to put up all over?
Sorry, I forgot to mention, I want to make it an even comparison, I want to compare an old fashioned 60W flood light bulb and a LED flood light bulb that uses 5W but gives off 60W worth of light.

**manshowrox13** · 03-18-2009, 04:42 PM

1 Day Usage Incandescent
60W X 12h X $0.13/kWh X 1kWh/1000Wh = $0.0936 per day

1 Day Usage LED
5W X 12h X $0.13/kWh X 1kWh/1000Wh = $0.0078 per day

So using the LED bulb instead of the Incandescent will save you $0.0858 per day, but you'll have to invest $10 ($15-$5) more up front. How long will it take you to make back your initial investment? $10/$0.0858 = 116.55 days (about 1/3 of a year). This is called the simple payback point.

But there is another important factor, the life of the bulb. Generally incandescent bulbs are rated to last about 3000 hours, while LEDs can last 30000 hours. You leave this light on 12 hours a day, or 4380 hours a year. This means the LED will last 6.85 years (30000/4380), while the incandescent would have to be replaced about every 8 months. In other words, you will have bought 10 incandescent replacement bulbs before you have to buy 1 replaced LED.

OK, lets put it all together. 10 year costs for LED vs. Incandescent
Incandescent: $0.0936/day X 365day/yr X 6.85 + $5/bulb X 10bulbs = $234.02 (for the electricity) + $50 (for the bulbs) = $284.02
LED: $0.0078/day X 365day/yr X 6.85 + $15/bulb X 1 bulb = $19.50 (for the electricity) + $15 (for the bulb) = $34.50

All in all, you would save $249.52 over the course of 10 years by purchasing the LED bulb! Hope this helps

03-18-2009, 04:42 PM

this line of reasoning gets very messy becuase the LED is providing a cash dividend (not paying a debt obligation is financially the same as earning money). Because you are getting the cash payment immediatly, you have to compound the $ value you receive in savings.

See, I told you it was messy. Personally, I'd say just spend the $15.00. The convenience of not having to change the bulb is worth the money.

03-18-2009, 04:43 PM

I don't know much, but it appears that the LED bulb as expensive as it is will pay for itself in less than a year. The old saying is right, you have to spend money to make money.