Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Is my dad right?

  1. Oct 17, 2005 #1
    Well I'm 17, and my dad is a home inspector, and thinks he knows everything. He is CONSTANTLY yelling at me because I leave every light on in their two story house. He says this raises the eletricity bill DRASTICALLY, and that they cant afford a couple of extra lights to be on. In fact, he made me turn off the light where I have to type on so I can't see the keys I typing on.

    He even replaced every light in the house with a very dim lightbulb, and everytime they leave they leave every light off to save eletricity. They also leave the AC off at night (its arizona and very hot) to save eletricity, as wel as leave it off in the day.

    A friend of mine I thikn on this forum told me leaving a couple extra lights on will only save you 50 cents a year. Is this true?

    Thank you
  2. jcsd
  3. Oct 18, 2005 #2


    User Avatar
    Gold Member

    $.50 a year??? You wish! Probably more along the lines of $.50 a week!

    Lets say you're running that 60watt bulb for 8 hours at night at (i think arizona is rather pricey) $.13/kwh.

    8hours * .060kw = 0.48kwh/day * 365days/year * $.13/kwh ~ $22.75/year per lightbulb.

    Get compact-flourescent bulbs. They only run on about 1/4-1/5 the energy per bulb and they last for thousands of hours (they cost about $4 but you end up going through like 8 normal bulbs in that same amount of time so it doesn't cost more for initial investment really).
  4. Oct 18, 2005 #3
    In AZ it costs about a quarter a day to leave your CPU running on full power, and about 8 cents a day with a 60w light bulb on all day. We have 3 computers running all day, + monitors, but that doesnt take into account the standby mode and power saving features.
  5. Oct 18, 2005 #4


    User Avatar
    Science Advisor
    Homework Helper


    You'll have more of a leg to stand on when you start paying for your own electricity! :)
  6. Oct 18, 2005 #5


    User Avatar
    Gold Member

    Our electriicty bill here runs around the average rental price for an apartment :P
  7. Oct 18, 2005 #6
    There is more to it as you are loading your A/C by 0.02 tons per bulb:frown: Start practising keyboard fingering and you can play blindfold:tongue: .

    PS: Your dad is right. A kW saved is a kW generated.
  8. Oct 18, 2005 #7


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Quark took the words from my mouth. The cost of the bulb includes the power to light it plus the power to remove the heat from the room. In Arizona, you must have AC running all the time. I wonder how much that adds? :yuck:
  9. Oct 18, 2005 #8
    I agree on everyones math and all, but sometimes people get a bit carried away when it comes to stuff like this. For instance, when you leave a room and come back in less than 5 minutes I would much rather leave the light on. Cycling most lights seriously shortens their life. When it comes to energy conservation (especially in cars) most people forget about the amount of energy it takes to replace something.
  10. Oct 18, 2005 #9


    User Avatar

    Staff: Mentor

    Lets start with some little picture numbers. In most places, a kWh of electricity costs about $.12 (you can ask your dad how much it costs where you live. So a 100w (.1kW) light bulb burning for one hour costs $0.012. That might not sound like much, but as Penguino said, it adds up. Lets just talk about you, though: If you had two of those in your room and used them for 4 hours a day, that's 12kWh or $1.44 a month. Figure the air conditioning requires about as much energy to take that much energy out of the room, so always double it. And lights are just the beginning - a computer uses about 300w.

    Now, when I was a kid I tried offer my parents a quarter a load to dry my clothes in the dryer, but they wouldn't go for it. It doesn't sound like much when it's $3 a light, but when it's $200 a month, it does. The only room you really have to argue (besides offering money) is if your parents aren't doing things like using compact fluorescent lgihts.

    My personal perspective differs somewhat from others' though. I ask myself: what is it worth to be comfortable in my own home? The answer for me is that it is a requirement. I have a roommate and we have a similar philosophy, so we always have the a/c on in the summer (with a set-back temp during the day when we're not around).

    Electric and gas (if you have it) run me about 10% of my monthly costs for living in an apartment ($50 out of $500). During the off-seasons, we spend maybe $30-$50 on our energy, and during the hottest part of the summer and coldest part of the winter, as much as $180. The point is, I calculate my cost of living based on the assumption that I will be comfortable. If it means I average an extra $25 a month to do it, then I factor that into the cost of living prior to moving. If that means I need to get a slightly smaller apartment/house, then so be it. Comfort is an important quality of life issue to me.

    My dad is the same way as yours: I think mine (I don't know your particular situation, but mine does have the money) is frugal to a fault. I once told him that "life's too short to drink cheap beer": if it costs an extra $3 a case to get beer that you like instead of just beer that you can stand, you should do it. But that was after I (the last of the kids) moved out, and parents find their financial obligations ease up quite a bit when that happens.
    Last edited: Oct 18, 2005
  11. Oct 18, 2005 #10
    Convice your dad to replace the dim condescent bulbs with bright compact flourescent bulbs. The cost of these has come down a lot (about $4 for a 15w bulb) and they work much better than they did 10 years ago. A 15w buld gives the same amount of light as a 100w incandescent bulb and the CF bulbs can go down to about 5w. Big money savings. The cost of the bulb can be recouped in about 300 hours of use (estimate no AC included) and you typically get 6 months to a years worth of usage out of these CF bulbs. These do save money in the end.
    Last edited: Oct 18, 2005
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?