Thread: 230V Light bulbs

1. But 1hz is one cycle which includes 1 peak and 1 troff. If you have 60hz and cut off all the peaks you still have 60hz.

I may be wrong here, but I am almost positive this is right...

-Max  Reply With Quote

2. I'm tired, I'm going to bed, I dont have time for electricity 101.. so I'll get back to this tomorrow...bye   Reply With Quote

3. Power = volts x amps. (Watts law)
Amps = volts / resistance. (Ohms law)
So with simple substitution we get the following:

Power = volts x volts / resistance, or simply volts squared / resistance.

Now, resistance is a constant for your light bulb. So the only thing that changes is the voltage you run it at. But since power varies as the square of voltage, if the voltage changes by a factor of 2 the power will change by a factor of 2 x 2, or 4.

So if you decrease the voltage by 1/2, the power will drop by 1/4.

Wasn't that easy?   Reply With Quote

4. Lessee P=E x I: 50=115 x 0.435, 100=230 x 0.435. The current doesnt change on these bulbs, the voltage and filament resistance does.
You have one 115V 50watt bulb and one 230v 100 watt bulb.
R= E/I so the filament resistances are respectively 264.3 Ohms and 528.7 Ohms.
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If you have 60 Hz (cycles per second) thats 8.3 mS positive voltage cycle and 8.3 mS negative voltage cycle. Removing the negative voltage cycle will leave a zero volt condition for 8.3 mS during the complete cycle resulting in only positive voltage cycles at .. n/m--
I you have a bridge rectifier connected to 60 Hz AC you get 120 Hz ouput.
If you put a single diode in series with that circuit, you only get 30 Hz out. Clear as mud? I think AC vs pulsating DC is where the confusion is occuring.  Reply With Quote

5.  Originally Posted by mliptack I also don't understand why it would be 25watts. The relationship is fairly linear.
-Max
"If you have two 100 watt bulbs, one designed for use at
110V and the other at 220V, the 220V bulb will have four times the
resistance of the 110 watt bulb. This is because the power used by a device
or resistance R when used at a voltage V and current I is given by:

P = IV = V^2/R

So when the 220V bulb is used at 110V, the power used is 25 watts, since the
voltage is halved and power goes like the square of the voltage. Since the
resistance of the filament increases with temperature, the current is
somewhat higher than 1/2 the current at 220V, but you will see a very dim
filament.

So you will use less electricity if you replace the bulbs in your house with
220V bulbs, but your house will be very dark."  Reply With Quote

6. This is getting f'cking ridiculous. I was going to replace a 60 watt 120V bulb with a 100 watt 230V bulb. I was using the 50watt example to simplify.
Nevermind- I found one. I'll either do that or wire my dual fixtures in series instead of parallel and use 2 120V 100watt bulbs..  It may be dark.. we'll see...   Reply With Quote

7. wow.
You know that it'll also put out a higher percentage of IR to visible light (lower efficiency)? how about installing a compact fluorescent instead?

it's likely the bulb will run a bit over 25&#37; because the filament temperature and thus resistance will be lower than when it's at full power.  Reply With Quote

8. Yeah, ok this all makes sense. Thanks everyone. I am running several compact florescents already, I just like a regular tugsten for color balance in some rooms.. and tired of changing light bulbs. I could fork out for the 'long life' bulbs but are they really? I mean, does anybody hook an hour-meter to a 2000-hour bulb vs a std 750-1000? heh--  Reply With Quote

9.  Originally Posted by steve-o The current doesnt change on these bulbs, the voltage and filament resistance does.
Wrong. The filament resistance is the same. The filament *IS* a resistor, remember? It's constant. The voltage changes, because you're plugging it into a 115V socket instead of a 230 volt socket. And since the voltage changes, so does the current. (Lower voltage through the same resistor = less current.)
You have one 115V 50watt bulb and one 230v 100 watt bulb.
R= E/I so the filament resistances are respectively 264.3 Ohms and 528.7 Ohms.
And if you take the 230V 100 watt bulb and put 115 volts across it, you will get .218 amps flowing through it, giving you 25 watts. (.218 x 115 = 25 watts)

Seriously, where did you get the idea that the resistance would change based on the applied voltage? Resistance is a constant. (Except for something special like a thermistor which is designed to change it's resistance as it's temperature changes, but that's *not* how an incandescent bulb works.)  Reply With Quote

10. OK Adam I'm talkin' about 2 different bulbs. - A 100watt 230 and a 115V 50 watt... ok?  Reply With Quote  Posting Permissions

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