Physics Ownage
lolfighter
Snark, Dire Join Date: 2003-04-20 Member: 15693Members
Snark, Dire Join Date: 2003-04-20 Member: 15693Members
in Off-Topic
<div class="IPBDescription">Fluorescents should not be left on</div> So today I was the last one out of the classroom, and I turned off the lights after me. The girl in front of me turns around and says: "You didn't have to do that, we'll be back in fifteen minutes." "So?" I reply, "I'm still saving power." Her answer? "No, because fluorescents use one hour of power every time you turn them on."
Ugh. I'd been told that once in the third grade I think, and at that time I had no reason to question it. After all, a grown-up had told me so, and grown-ups were so much smarter than me. I later figured out that they were probably just trying to prevent me from playing with the light switch. Around the ninth grade or so I picked up on the problem again, and calculated that this made absolutely no sense at all. Back to the story:
"Nah, that's not true." I replied.
"Yes it is"
"No it ain't"
"Yes it is"
Doing fine so far eh? So I tried the other approach: reasoning. After all this IS a technical education we're taking, so she'd probably be open to theoretical evidence. Cue the basic formula:
V x A = W
V = Volt ; A=Ampere ; W=Watt
I assumed that a normal fluorescent tube is around 30W, might be a bit more or less actually. Denmark uses a voltage of 220V, so
A=30/220
That's A = 0.136
Not much actually.
So next I assumed that a normal fluorescent takes about five seconds to turn on, once again it might be a bit more or less, but I'm certainly not entirely off. If a fluorescent was to use the same power it uses in an hour (30 Wh or 0.03 kWh) during the span of five seconds, it would use 720 times as much power during these five seconds as it normally does. An hour has 3600 seconds, 3600/5=720.
So when you turn it on, a fluorescent uses 720x30W=21600W on that flickering stuff, right? So, once again using V x A = W, we can conclude that
A=21600W/220V=approx. 98A
So, an amperage of 98A eh? A normal fuse will blow at around 15A, and normal wiring can't take much more than that either for very long time. Imagine turning on ALL of the fluorescents in an ENTIRE ROOM (typically there's 12 - 16 of them) AT ONCE! That'd be up to 1.5kA. Safe to say I'd probably take the entire building off the net if I could flick the switch in two or three rooms simultaneously.
So if you are still one of those who believe that fluorescents use an hour of power every time you turn them on: Think again. Or perhaps just THINK. <!--emo&:p--><img src='http://www.unknownworlds.com/forums/html/emoticons/tounge.gif' border='0' style='vertical-align:middle' alt='tounge.gif'><!--endemo-->
Ugh. I'd been told that once in the third grade I think, and at that time I had no reason to question it. After all, a grown-up had told me so, and grown-ups were so much smarter than me. I later figured out that they were probably just trying to prevent me from playing with the light switch. Around the ninth grade or so I picked up on the problem again, and calculated that this made absolutely no sense at all. Back to the story:
"Nah, that's not true." I replied.
"Yes it is"
"No it ain't"
"Yes it is"
Doing fine so far eh? So I tried the other approach: reasoning. After all this IS a technical education we're taking, so she'd probably be open to theoretical evidence. Cue the basic formula:
V x A = W
V = Volt ; A=Ampere ; W=Watt
I assumed that a normal fluorescent tube is around 30W, might be a bit more or less actually. Denmark uses a voltage of 220V, so
A=30/220
That's A = 0.136
Not much actually.
So next I assumed that a normal fluorescent takes about five seconds to turn on, once again it might be a bit more or less, but I'm certainly not entirely off. If a fluorescent was to use the same power it uses in an hour (30 Wh or 0.03 kWh) during the span of five seconds, it would use 720 times as much power during these five seconds as it normally does. An hour has 3600 seconds, 3600/5=720.
So when you turn it on, a fluorescent uses 720x30W=21600W on that flickering stuff, right? So, once again using V x A = W, we can conclude that
A=21600W/220V=approx. 98A
So, an amperage of 98A eh? A normal fuse will blow at around 15A, and normal wiring can't take much more than that either for very long time. Imagine turning on ALL of the fluorescents in an ENTIRE ROOM (typically there's 12 - 16 of them) AT ONCE! That'd be up to 1.5kA. Safe to say I'd probably take the entire building off the net if I could flick the switch in two or three rooms simultaneously.
So if you are still one of those who believe that fluorescents use an hour of power every time you turn them on: Think again. Or perhaps just THINK. <!--emo&:p--><img src='http://www.unknownworlds.com/forums/html/emoticons/tounge.gif' border='0' style='vertical-align:middle' alt='tounge.gif'><!--endemo-->
Comments
But yeah, she could kinda see my point.
in class right now
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EDIT: It pays to turn off your fluorescent lights. While it is true that the life of a fluorescent lamp can be shortened a bit if it is turned off and on frequently, the energy cost savings far outweigh the cost of these lamps and any small additional amount of start up energy during their lifetime. According to what I read, the balance point is about 10 minutes. The lights should definitely be turned of if nobody will be in the room for this amount of time or longer.
:: flick :: :: flick :: :: flick :: :: flick :: :: flick :: :: flick :: :: flick :: :: flick :: :: flick :: :: flick :: :: flick :: :: flick :: :: flick :: :: flick :: :: flick :: :: flick :: :: flick :: :: flick :: :: flick :: :: flick :: :: flick :: :: flick :: :: flick :: :: flick :: :: flick :: :: flick :: :: flick :: :: flick :: :: flick :: :: flick :: :: flick :: :: flick :: :: flick ::
<!--emo&:p--><img src='http://www.unknownworlds.com/forums/html/emoticons/tounge.gif' border='0' style='vertical-align:middle' alt='tounge.gif'><!--endemo-->
so off, wait 7, turn off you have a net loss of 3 mins
the electricity saved would be near 0 cents
the cost of the lightbulb 'wasted' would be slightly less
it doesn't really matter unless you:
a) have a HUGE rig or
b) have a compulsive flicker
c) really really love to pinch fractions of pennies
No. If you won't be in the room (or anybody else), for 10 minutes or more, you should turn off the light. With this, you'll save more money on energy, than if you would leave the light on. And although you shorten the lifetime of the light by turning it off and on in such short intervals (10 minutes or a bit more), a new such light will cost less than if you would leave it on all the time and use up the energy... All right, I really must have confused you now. <!--emo&:)--><img src='http://www.unknownworlds.com/forums/html/emoticons/smile.gif' border='0' style='vertical-align:middle' alt='smile.gif'><!--endemo-->
But yeah, she could kinda see my point. <!--QuoteEnd--> </td></tr></table><span class='postcolor'> <!--QuoteEEnd-->
good to hear people can still listen to reason
<!--emo&:D--><img src='http://www.unknownworlds.com/forums/html/emoticons/biggrin.gif' border='0' style='vertical-align:middle' alt='biggrin.gif'><!--endemo-->
But even if they arnt what does a few cents matter in the long run, also why didn't you **** SLAP that girl in the face for questioning you. <!--emo&:angry:--><img src='http://www.unknownworlds.com/forums/html/emoticons/mad.gif' border='0' style='vertical-align:middle' alt='mad.gif'><!--endemo-->
What you takin bout! <!--emo&:p--><img src='http://www.unknownworlds.com/forums/html/emoticons/tounge.gif' border='0' style='vertical-align:middle' alt='tounge.gif'><!--endemo-->
Or so you say. <!--emo&;)--><img src='http://www.unknownworlds.com/forums/html/emoticons/wink.gif' border='0' style='vertical-align:middle' alt='wink.gif'><!--endemo-->
I smell a woman... Get back in the kitchen! <!--emo&:D--><img src='http://www.unknownworlds.com/forums/html/emoticons/biggrin.gif' border='0' style='vertical-align:middle' alt='biggrin.gif'><!--endemo-->
Haha, no. I'm kidding. I meant no offense to women or anyone else.
PS: We're going way off topic...
It's the OFF TOPIC FORUM!
I heard that the fluorecent lights in tunnels (as in tunnels cars-go-under-them tunnels) will break about 50% of the time if they're turned off, since they're designed to be NEVER turned off, and they don't seem to like it very much if they have to switch off for whatever reason.
Isn't this such a facinating topic, I mean, fluorecent lights! Arn't we all such a cool, exiting group of people? <!--emo&:D--><img src='http://www.unknownworlds.com/forums/html/emoticons/biggrin.gif' border='0' style='vertical-align:middle' alt='biggrin.gif'><!--endemo-->
<a href='http://lightingdesignlab.com/articles/switching/switching_fluorescent.htm' target='_blank'>Switching Fluorescents</a>
BZB
<a href='http://lightingdesignlab.com/articles/switching/switching_fluorescent.htm' target='_blank'>Switching Fluorescents</a>
BZB <!--QuoteEnd--> </td></tr></table><span class='postcolor'> <!--QuoteEEnd-->
noooo help its reason! ahhh evidence! IT BURRRNS
Yes, I realize that I should have made with the slappij (cue :rolleyes:), but I'm such a nice person, I just couldn't do that. And slapping girls is not the way to get them to like you I hear.
If anyone should be slapped, it'd have to be Nil_IQ for questioning the conversational value of fluorescent tubes. <!--emo&;)--><img src='http://www.unknownworlds.com/forums/html/emoticons/wink.gif' border='0' style='vertical-align:middle' alt='wink.gif'><!--endemo-->
Compare this to the hall light just outside my door that gets shut off maybe once a month. (Both flourescents mind you)
It's lasts 5 years at a time!
Now, my old bedroom light was actually two bulbs... so... would I say saved electricity was worth it? Probably not.
Then again, I live in British Columbia, (Canada) where Hydro-electric power is so bountiful that we just pretty well give it away free to places that aren't so lucky, like California for example!