# Question about incandescent lights and how frequency relates



## young AF electrician (Aug 6, 2007)

My Supervisor asked me a question today that's driving me crazy. He asked me what would happen to an incandescent light if I upped the frequency to 80htz, or lowered it 40htz, and why. I'm very aware of the effects of voltage and amperage on a light bulb, but I've never thought about how frequency affects it before, and it's really got the gears turning but I haven't been able to figure it out. Kinda hoping I could get some more experienced help with this one. I've been trying to research it myself, but all I get is search results about the frequency of the light being produced, not the light bulb itself. I've only been in the career about 4 years now and I deal with a lot more than just power plant generators and electricity, so I'm still learning a lot of this for the first time. My only thought so far is that if you raise the frequency than you lower the amperage, but I'm not convinced that that would make any real visible difference.


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## MDShunk (Jan 7, 2007)

Probably nothing. It's just a resistor. 

If you lowered enough, however, you eye may detect the flicker.


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## frenchelectrican (Mar 15, 2007)

As what MD say about the indscent bulbs the filment useally dont bother with the frequency but if you get below about 40 HZ or less it will make very notibale frequency espcally if you run on old 25 Hz system it will make ya go nuts in some way but run it in very high HZ system like 400 HZ it will not even noticed at all 

but flourscent and HID that diffrent story try run on 25 HZ they will flicker as well and also put in insane loading on the ballast as well [ i think in other forum i did see one photo of 25 Hz ballast dang that look huge ] but ramp up at 400 HZ or higher you will not even notice at all 

Merci Marc


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## frank (Feb 6, 2007)

Can't think of anything myself except to state the obvious. There would be a change in light spectrum and consequential changes of stroboscopic effect. But the lamp itself I do not think would be effected. 

Frank


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## Jim (Jun 12, 2007)

I concur with all the other posts; however nobody has addressed the magnetic effect of the higher frequencies with regards to filament metal fatigue possibly shortening the life of the lamp.


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## 220/221 (Sep 25, 2007)

I thought that dimmers worked basically by lowering the frequency and the filiment would not get a change to heat up to bright white???:blink:


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## 480sparky (Sep 20, 2007)

220/221 said:


> I thought that dimmers worked basically by lowering the frequency and the filiment would not get a change to heat up to bright white???:blink:


And I thought dimmers worked by 'chopping off' the higher ends of the sine wave. The wave would rise from zero, then at a certain point determined by the setting of the dimmer, it would flatten out, then return to zero.

Adjusting the frequency seems like a fan speed control???


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## 220/221 (Sep 25, 2007)

Hey, I'm an electrician not a rocket scientist.

All I really know is that they get hot and people are ALWAYS complaining about it.


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## JohnJ0906 (Jan 22, 2007)

480sparky said:


> And I thought dimmers worked by 'chopping off' the higher ends of the sine wave. The wave would rise from zero, then at a certain point determined by the setting of the dimmer, it would flatten out, then return to zero.


That is my understanding as well. That is why a regular dimmer won't work on a transformer. (Low voltage lights, etc.)


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## 480sparky (Sep 20, 2007)

Current dimmers have a TRIAC that switches or "chops" the AC sine wave and automatically shuts the light bulb circuit off every time the current reverses direction -- that is, whenever there is zero voltage running through the circuit. This happens twice per cycle, or 120 times a second. It turns the light circuit back on when the voltage climbs back up to a certain level. Turning dimmer up, the "On Cycle" is longer, the lights are brighter. Turn Dimmer Down, the "On Cycle" is shorter, the lights are dimmer.

Without a dimmer:










With a dimmer:


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## rbj (Oct 23, 2007)

Great graphics 480.


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## young AF electrician (Aug 6, 2007)

*Thanks for the help*

Appreciate it guys. Turns out he was just expecting the easy answer, that amperage goes down and extends the life of the bulb but only to a very minor extent. He's been asking me a lot of little questions like that, trying to get me really thinking about how electricity reacts in different circumstances. Turns out he's a pretty awesome boss.


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## gilbequick (Oct 6, 2007)

What other questions has he been asking you?


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## young AF electrician (Aug 6, 2007)

Mainly more generator specific questions lately, like the benefits and drawbacks of hooking up alternator winding leads in either series or parallel, what different voltages you get from different compbinations, and how it all affects frequency. I've been able to answer those pretty well though.


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## JohnJ0906 (Jan 22, 2007)

young AF electrician said:


> He's been asking me a lot of little questions like that, trying to get me really thinking about how electricity reacts in different circumstances. Turns out he's a pretty awesome boss.


You're lucky to have a boss like that. Learn all you can from him.

I had too many who answered questions with " 'Cause I said to do it that way", or the ever-popular "That's the way we have always done it"


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## Percheron49 (Jan 26, 2008)

Well, frequency affects the voltage potential. From what I remember of my physics classes, as the frequency goes up it causes the RMS value of the voltage to go up due to the Cos theta of the wave angle which could cause the light to burn brighter.


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## randomkiller (Sep 28, 2007)

I have seen regular bulbs on 50 cycle current and as MD said you can see the flicker with your eyes. I don't think increasing the freq would change more than the life of the bulb.


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## surfbh (Jun 1, 2008)

Increasing the frequency would increase the inductive reactance and the capacitance while lowering the capacitive reactance. More than likely this will increase the impedance. Ask him to show you how to reach resonant frequency!:thumbup:


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