DC Incandescent Bulb

I'm not sure, but I think this bulb will give longer life on 220 VDC than on 230 VAC. If nothing else, try one out. If it blows in short order, then I'm wrong, but I would be willing to bet the price of one bulb on this.

It's worth the risk of one bulb as an experiment.

No problem , you can use it safely.

You can simply use the incandecent lamp in Dc which is designed in AC. Whatever may be the supply it dependes on the time required to heat up the fillament. In other case where inductor and other reactances are involved DC can not be used.

Both you and Tornado suggest the bulb life will be better with continuous current. Is this due to the fact that with DC there will be no off time and thus no thermal cycling at 60Hz?

The slightly less voltage is the main thing. That will give a bit less amps and watts as well. The bulb will not be quite as bright, but will last longer. Same principle as using 130-volt bulbs on 120-volt circuits. I'm not sure about the lesser thermal cycling--can't hurt,might help.

I think you cannot measure any difference in bulb life due to this reduction in operating voltage.

Remember, these are emergency lights. They are off 99.999% of the time.

Interesting discussion.

As others have said, probably (although AC lamp life running DC is debatable, and you definitely will need to test), but what is the application? You mention 'emergency lighting', do you mean building emergency lighting? If so you may not be legally allowed to use ac incandescent lamps in this application (as per your local electrical regulations and building emergency lighting standards and codes).

Can you please provide more information on exactly what you are doing along with country.

Normally yes.

A typical mains power supply is specified as (something like) 230Vac +10% -6%, (so 220V is within range).

The RMS ac value of the globe is equivalent to its DC rating.

Reading down from the top, yours was the first correct and factually correct post.

A GA from me.

Some of the others who posted before you leave a lot to be desired, most were totally wrong in some way or another.

I liked the one about the electrons from someone else, it was really quite funny!

It would appear the poster has some experience with "fluorescents" on DC (as I have also!!) but no real good knowledge of how incandescents work well on DC (perhaps he forgot about his "DC" car when posting?)

The post that you found 'funny'... is quite correct.

For dc operation the bulb MUST be derated to give an equivalent life to working at dc, this is usually about 10% of the rated ac working voltage.

Carl Pugh is quite correct, as other posts after mine should show....

Wrong again I'm afraid....

Please be so kind as to post a reliable website that this "phenomena" you ascribe to DC is clearly and fully described.....

My apologies, but otherwise you are simply not believable in the slightest.... as its basically an "Old Wive's Tale", nothing more, nothing less.....

My personal opinion is that only people who have not studied Electrical Engineering will probably actually believe it...... or downright amateurs....corner shop electrical people and jobbing electricians....

The old fashioned incadescent bulbs run fine on DC.

The power is simply the RMS of the supply.

If you reduce the voltage below rated the bulb runs cooler.

Increase the RMS voltage and it runs hotter, by approximately the square of the voltage. (The bulb resistance will increase slightly with higher temperature, but not enough to save you from the voltage squared effect).

If the lamp lasts, it'll last a lot LESS longer at 220 Vdc than it will at 230 Vac. Adn what it'll likely do is burn up immediately.

What matters isn't the voltage, but rather the poiwer dissipated in the incandescent wire, which is nothing more than a high-wattage resistance.

The equation for calculating DC power is: P = V(squared) / R = voltage(squared) divided by resistance.

The equation for calculating AC power is similar, but not identical: P = Vrms(squared) / R.

Note the difference: in this case, DC power is generated by a voltage of constant intensity put across a resistance. However, AC power is generated by an EFFECTIVE voltage that over time is the area under the voltage wave on a graph. In the case of a sine wave (which is what utilities provide), that effective voltage is Vpeak / root(2)

When we give a figure for a DC voltage, the figure that we give is that of the constant DC voltage, say 220 Vdc. When we give a figure for AC voltage, the figure that we give is for PEAK voltage of a voltage signal shaped like a sine wave. The actual power delivered by a sine-wave voltage is:

Pac = Vrms(squared) / R = (Vpeak / root(2))(squared) / R = (Vpeak / 2R).

So AC PEAK voltage delivers only HALF the power as DC voltage that has 'the same voltage'.

This means that if the bulb draws 60 Watts at 230 Vac, that is it's incandescent wire emits 60 Watts of energy as heat and light at 230 Vac, it'll emit TWICE as much (that is, 120 W) at 230 Vdc. At 220 Vdc, it'll emit a bit less (220 / 230)(squared) times 120 Watts.

If your lamp's wire doesn't burn out immediately (which it very likely will), it'll certainly up a lot faster on DC than if it were used on AC of the 'sme voltage'.

Cheers! DZ

Uuuuhhhh .. heh-heh .. How about that, huh?

How embarassing; you're absolutely right.

*Humiliation* DZ

P.S. Mind you, humilation's GOOD for a man once in a while. :D

Take an oscilloscope and see how the voltage builds up. How much is the peak amplitude on a 220 Volts AC net?

220√2. The RMS voltage is still 220, as DZ saw immediatly on being reminded.

Thanks Tornado, You are correct. My excuses.

No problem. Every now and then I stick my own foot into my mouth (or keyboard). The occasional butt-kick is good for bringing one back onto the path. Somebody called me a knuckle head once, and I gave him a well deserved GA. Sometimes the best laughs are on oneself!

Sorry to all. I went completely wrong. Made the test myself. The peak amplitude goes far over 220 - Interpreted RMS wrong.

Take an oscilloscope and a photo transistor and see what wave form you get. At 50 or 60 Hz the filament does not have time to cool down very much. this can be easily demonstrated by using a fan blade on a DC motor with a variable supply. with fluorescent light you get noticeable stroboscopic effects but with incandescent the effect is greatly reduced, if noticeable at all.

The peak voltage on 220V is 1.414 x 220 = 311V, but the RMS value (In Spanish they use a rather more obvious term "Voltaje efectivo") is just that the effective voltage and the equivalent to DC, as has been given by several other posters above.

Regards

Chas

GA

Rubbish.

Further rubbish!

On AC chances is there that on switch-on it is near zero-crossing

or

at peak i.e. V x 1.14 Volts

But on DC it will always at 220 nnominal [as some call 230V ]

When switch-on the bulb is cold & has minimum resistance and chances are there in DC or AC to flash it off due to peak surrent bue to slugishness of rising the temperature of element to limmit current to minmum.

Great answer and fully accurate. (there are very few knowledgable people on this blog...you are one of the good ones!!!)

sorry don't agree, see my reply

Rubbish.

It may look good to the uninitiated, but its wrong.

"Close but no cigar"

Hi Dread,

Your way out. We use regular low Voltage bulbs at both 50Hz and DC no noticeable difference in lifespan.

One BIG difference is with Halogens which are spec'd at 12 or 24V being put on dc is that generally, where batteries are involved, "24Vdc" is not 24V but anywhere from 24 to 28.5. This reduces their life from 1000s of hours to 100s of hours.

Since in the OPs case these lamps are fed from a charger, which is probably a fixed voltage charger set at float level it wont be a problem. When the batts are feeding the lamps they will be a little dimmer.

regards

Chas

The bulbs never get damaged while glowing. it fails only during switch on. the reason is the cold bulb resistance is very much lower, hence a huge surge in in-rush current. I² R is the power generated. the spot at which the filament wire is very thin gets burnt due high hot spot temperature. To protect incandiscent bulbs one has to use suitable negative temperature coefficient resistance in series with it. This way we can prolong the life of the bulb. The problem will be the bulb will glow dimmly initially and will go to full brightness in seconds.

Have you never seen an old bulb with the glass all metalized? That is metal transfer from the filament to the glass. Incandescent bulbs do have a finite life.

Miniscule gas leakage also leads to slow oxidation of the element.

Yes, vibration and thermal shock are still the number one failure modes.

Thats a really bad explanation.

I know where you wanted to go, but you will have to explain FAR better if you ever want a GA from me......

You are making some serious elementary errors.....

The value given of an AC voltage is the equivalent of the "work" that a DC voltage of the same value can do...

The "Peak" voltage of any given AC voltage is far higher than the "given" value of 110 or 220 volts (for example) for that reason......

Here is a good web page that explains in a simple but correct manner with pictures and simple words the relationship between AC & DC voltages:-

http://www.bcae1.com/voltages.htm

No problem , you can use it safely.

Guys, it amazes me that so many of you have forgotten DC circuits 101! YIKES!

The ONLY consequence of using a AC bulb on a DC will be that you will sputter away the filament preferentially on one side, but the difference in life should not be much because in AC mode it would be sputtered away on both ends instead of one, especially since you will be operating at about 5% below nominal rating.

Don't forget that Edison's bulbs were originally intended to be used on DC, it was that damned upstart Tesla that complicated things with his polyphase AC distribution system. =b

Also, Edison first discovered the thermonic effect by noticing that the bulbs in his long term test fixtures always had a shadow on one side of the bulb due to thermonic sputtering. Edison should rightfully be credited with the discovery of the vacuum tube.

Tesla was indeed rather flashy (and a bit weird). However, Charles P. Steinmetz probably did more to advance AC and polyphase motors.

There is (or was) a play, A Peek into the Twentieth Century, built around the controversy between Thomas Edison and George Westinghouse over DC versus AC power transmission. A key plot feature involved the first person to be executed in an electric chair (AC). Edison exploited this by deriding AC as "the executioner's current." The play may be hard to find (I saw it in trials at the Seattle Repertory Theater). Fascinating.

I am unsure of details, but I think that in his work on "large" phenomena, Tesla made valuable discoveries on high voltages, short circuits, and transient events. Perhaps less so on workhorse industrial applications. I don't know to what extent Ayn Rand used him as a prototype for John Galt. She almost certainly wouldn't have used Steinmetz, who was a socialist. Steinmetz surely contributed more to GE than he drew in salary. One might think "chump," but I suspect he got off more on theory than on wealth.

Lightning has high voltage and energy flux, but of very short duration, hence probably not much sustained wattage or energy value. I don't know the numbers, though. This reminds me of the category of people who don't know the difference between a kilowatt and a kilowatt-hour. The media muff this distinction repeatedly, as do many over-unity enthusiasts.

Some good infos and also some incorrect infos.

Look here:-

http://www.electronicstheory.com/html/e101-37.htm

That is ALL correct.

It was Dr. Fleming, working at Edison's English lamp firm who first described the physics behind thermionic emission, and created the Fleming Valve. Others, such as Lee Deforest, saw the effect - and made use of it, but never fully understood it.

And the lawyers all got rich.

Is there any Incandescent bulb in market rated only for AC?

Yes.

when I worked in the Steelworks on the 440 volt DC powered overhead cranes, for ALL internal lighting on the crane we would use 2, 240 volt lamps (in series) rated at 100 watt for AC voltage.

You will have no problems at all with your proposal other than the lamp(s) will not be as bright as they would be if supplied with the correct AC voltage.

However as they are only emergency lights I guess only to be on for a short time then it might not be a problem if you have sufficient to illuminate to an accepted level the area of escape. You should check if you have a minimum lumens per sq Ft requirement

Absolutely yes, and even more, if you have 220DC, the average power delivered will be exactly equal to that of your 220AC outlet, because those 220AC are rms volts, that means that even when actually the AC line is a sinusoid with 220 * SQRT(2) volts amplitude, the average power is exactly the same, with the advantage of no flicker and enhanced bulb life.

Even better if you have a soft start DC circuit, you may build it with a series inductor, say one of the windings of a transformer used as inductor, that way the bulbs will turn ON in a few tenths of a second instead of milliseconds. The life of modern high efficiency bulbs will be also enhanced provided they are of the AD DC compatible class.

Jaime Soto

Chile

GA for a really good commonsense answer!!!

The simple answer to your simple question: YES.

I have seen ordinary incandescent bulbs used for decades in the following situations:

• Emergency lighting on US Navy ships & submarines.
• Emergency lighting in older generating facilities.
• Normal lighting in off-grid facilities without AC, such as remote stations using solar panels with batteries (although these are rapidly being converted to LED lighting).

Now the extended response:

For emergency lighting, I would suggest using "Rough Service" bulbs, which have a thicker filament that is more resistant to vibration and mechanical shock. In your specific design, the bulbs will produce nearly the same light on DC or AC.

You should note that 230V is a nominal rating. The design range is +/-10%, or 207-253V. DC voltage will also not be constant. During charging the voltage will be higher than nominal; during emergency conditions (without a charger) the voltage will drop. Your emergency lights will dim as the batteries are discharged, just as a standard flashlight dims over time.

WOW! I didn't even know there was a DC incandescent lamp. I always thought lamps were the same for AC and DC. You learn something new every day.

Please elaborate on that.....to me personally it makes no sense at all......where and what did you read to convince you of that?

I posted a reply earlier stating that "I didn't know there was an incandescent lamp that was for DC". I did a little research on the subject and could not come up with a DC incandescent lamp. The only reference I could find was in the base configuration. They were usually screw terminals or bayonet, not medium screw base. All medium screw base lamps were for 110 to 250V and didn't specify alternating or direct current.

The conclusion I came up with was, "all lamps will work on AC or DC" with lamp life not being a factor. One further thing I found was concerning "emergency lighting" (EL). All the emergency lighting systems I found were for an AC input and a DC output. EL systems typically consist of a battery charger, battery and a 6-12V incandescent lamp or more recently, LED. I don't think lamps as large as 120 to 250 volts is used in EL systems. All the information I got was from the GE literature.

I agree with your comments here taken from GE literature.

I misunderstood your previous post completely....thanks for clearing that up for me (and any one else interested).

Remember, I would guess that more than 99.9% of all road vehicles have DC power systems, as do many boats/yachts etc etc.....DC or AC it makes no difference to an incandescent bulb.

All properly designed LED lighting can work on AC, therefore by definition also DC (as they mostly have recification built in!), either way round polarity wise, as long as the voltage does not exceed the AC specified (RMS) voltage.

Have a great day.....

[rated 230V AC,60w in 220V DC? emergency lighting fed from DC charger]

This question doesn't make sense. Why would a DC charger be supplying 220VDC? Batteries would have to be 220V. Why would you use such a high DC voltage for charging batteries? Battery chargers are usually 6,12,24 or 48VDC fed from an AC supply.

The post shows a strange approach. However, once the system switches to emergency, the transformer to charge the batteries in the circuit can also be used to transform a chopped DC from the charged batteries, up to 220 Volts. DC there doesn't look making sense indeed. The concept could be profitable if the fixture is also used as main light, as well as emergency light, using the same bulb.

Why are you talking about transformers? DC doesn't use a transformer. Do you mean a battery charger that operates off AC mains and is rectified to DC for charging? Your description is very confusing.

Does anyone ever read any of the posts BEFORE they post their answer?

67 posts.

8 good answers.

4 almost good answers.

Could this be a record?

Have a great evening gentlemen...

Off topic?? mea culpa. In this forum everyone has the possibility to give his/her answer to the question asked. We respect each opinion and try to give a correct answer. In this thread I was completely wrong because I misinterpreted the RMS value of AC. And that makes this forum just great. At the end, lots of info has been gathered and put together and each individual, when open minded can learn of it. Nobody is perfect and what his conclusion and standpoint is at the end, is his own decision, is his own interpretation. But statistically is the chance for a right answer greater with 30 answers than with one single. Fact is that when you feed your really bright 12 Volts car headlight with the same (RMS) voltage out of a AC transformer that is capable to deliver the 45, 50 or 70 Watts and you, respected Guest, look in it, you will see the same bright light, that hopefully will enlighten you too. Peace and welcome.

Assuming that is your thoughts/knowledge on the subject, not only you demonstrate what a complete and utter ignorant person you are. simultaneously you display a total lack of electrical knowledge to boot.........

Now if you meant it as a joke, thats slightly better, but many of us here still do not understand that as being much like real humour either.....

Either way, good that you posted as a guest!! Nobody knows who you are!!!

Some things I do for enjoyment, some things I do because I need money, and other things I do because I want to give something good back to this world before I leave it. Unfortunately I must have made that post when trying to relax after a long day pumping out flooded basements for people less fortunate than me (I am the Chief of the local fire dept) who live in some of the adjacent towns. I was proabably very tired at the time but didn't realize it when I "submitted" the posting. I am not 100% perfect, ask my wife she will verify that, and must have filled the "off topic" box when posting.

I try to make my posts easy to understand, without extensive theory and easy to implement is possible. Thank you for not bashing me as some posters are sometimes more interested in disproving someone elses post than they are interested in answering the original post.

"To err is human, to forgive devine"

You "over "erred on the "safe" side......if thats an "error"?

You post well and clearly with accurate info and a lot of common sense, thats what we need on CR4.....thanks.

An experiment for you all

Take two, 12v Halogen lights, connect one to the usual AC step down transformer, connect another to a 12 volt car battery, and let EVERYONE know the results.

Have fun!

No need, they would both work just fine.....

Hi Andy

I know it, you know it.... but a lot don't.. hence the experiment to prove it once and for all.

I would guess that very few will do it, the ones that really need to learn something will simply not believe the results........but it was a good idea of yours.

yes you are right..... I've found that it starts with only knowing half an answer, the rest is added sometime based on nothing and then it become gospel and anything that does not agree with those teachings/beliefs cannot be correct.

Well put.....

One detail I forgot on my advise to use inductive soft start for DC bulbs:

A flying diode pointing to the positive contact should be placed in parallel to the choke inductor, to prevent a spark on turning OFF the lights, due to the electric inertia of the inductor.

Jaime Soto

Chile

79 comments!!!!!!!!!!!(80 including mine)

I have not seen any post with this much comment.The GUEST might be happy!!!

Don't know his question is cleared.

But here in INDIA there is no DC incandescent bulbs available.......

Dear GIRI, what may I ask do you use in your car?????????

Or do cars in India work with AC?????

Sorry Andy....... i mean rated for that voltage & wattage.............

That should at least demonstrate that it does not make the slightest difference with regard to AC & DC through a lamp of the correct voltage......!!

I served on several RN ships where the main supply system was 220V DC, we used conventional household lamps for a lot of our lighting, especially in engine rooms or where damp might be a problem.

We also used Fluorescent fittings in some areas, but we swapped the polarity each day to prevent one end of the tubes burning out before the other, as the simple circuits we used then made one end the cathode and the other the anode (like in a valve), the cathode end would supply the electrons and would have got depleted first otherwise....that way we doubled the tube life....

(This effect will NOT be seen on incandescent lamps, so they did not need or get the polarity swapped...!)

I'm sorry Andy but you're very funny - LOL!!!

Not always intentionally though, but thanks anyway!!

so what's in a flash light?? and don't say LED's