# Does voltage of Lamps matter?

Discussion in 'The Projects Forum' started by Videodrome, Jan 2, 2010.

1. ### Videodrome Thread Starter Member

Nov 12, 2009
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0
i want to use a set of lamps in a guitar pedal. its pretty much 3 seperate pedals rehoused into 1 box for ease. all three of the pedals are powered either by 9v dc or 9v battery. i ordered some lamps but just realized that they are 12 v and was wondering if i ordered the wrong ones?

2. ### kubeek Expert

Sep 20, 2005
5,412
1,030
What kind of lamps? Do you mean light bulbs?
And anyway, if the voltage didn´t matter, would they bother to write it there?

3. ### Wendy Moderator

Mar 24, 2008
21,483
2,961
Yes, it matters. 12V bulbs will be dimmer, and draw a bunch more current.

If these are LEDs they can be adjusted with a resistor.

4. ### k7elp60 AAC Fanatic!

Nov 4, 2008
552
108
I disagree with you Bill on the current drain. The current will be less if they are incandescant bulbs. The life will be much, much longer. Yes they will be dimmer.

5. ### Wendy Moderator

Mar 24, 2008
21,483
2,961
When a bulb heats up to white hot heat it is at it's maximum resistance. When a bulb is dark or dim it is at it's minimum resistance. Since these bulbs will not achieve their total brightness they will suck a lot more current.

The difference between the two states is significant. I suspect we'll have to agree to disagree, but this is also subject to experiment if you really want to explore it.

****************

I'm wrong, I ran the experiment instead with a 12VDC automotive tail light

6V ..1.40 Amps . 4.28Ω
9V ..1.75 Amps . 5.14Ω
12V .2.03 Amps . 5.91Ω

I still suspect using the wrong the bulbs is not a good idea. You don't know what kind of wattage you're using instead of the correct one.

Last edited: Jan 2, 2010
6. ### SgtWookie Expert

Jul 17, 2007
22,199
1,801
As Bill said, incandescent bulbs (those with filaments) will draw quite a bit more current when they are cold than when their filaments are heated.

Voltage and wattage rating do make a difference.

7. ### k7elp60 AAC Fanatic!

Nov 4, 2008
552
108
Incandescant bulbs have some interesting spec's. The cold resistance is usually around 1/10 the hot resistance, because of this the initial surge current is high as one would expect, but it only takes a short time for the filament to reach hot temperature and a result of normal current. If one has ever noticed that most incandescant bulbs burn out when first turned on. Reducing the voltage on the bulbs really extends their life. The attached article is from Technical notes of Industrial Devices Inc.

As a side note, I developed a surge limiting circuit for 12V bulbs 10 years ago. I still use some for reading lamps. I changed my first bulb after 10 years several months ago.

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8. ### djb Active Member

May 17, 2008
31
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lower voltage --> lower current. Ohm's law that stands for bulbs, since the bulb is ohm's law obeyer.

Usually when you run a device on a power source with different electrical characteristics, you don't gain life, you shorten the life. But maybe for bulbs is right.