running incandescent bulb on DC

[Thunderchild]

the thought occurred to me, what if an incandescent bulb was run on DC ? could it last longer not being subject to the variation in voltage (fast flicker) would it produce a bit more light as it would not have a chance to cool down and this would maintain a constant high temperature and keep the resistance up minimising losses and make a bit more light ?

 

[Hero999]

Bulbs do last longer on AC but it's got nothing to do with the variations in temperature as the thermal time constant of the filament is much longer than the peroiod of the AC cycle. Bulbs last slightly longer when powered from DC as on DC more electrons are boiled off the negative end of the filament than the positive end so it wears out more quickly causing it to fail; this dosen't happen on AC becase the wear is shared more evenly on both sides of the fillament.

 

[Thunderchild]

aha now thats interesting what about more light ? I mean put a single diode on that ac bulb and you will see how it flickers so the alternating could be like constantly turning on and off but i suppose it is practically irrelevant

 

[audioguru]

An incandescent bulb with 230VDC will be exactly as bright as when it has a 230VAC sine-wave. The power is exactly the same.

When the AC is rectified then the metal filament is cooler, so its resistance is less, so it uses more than half the power as without a rectifier.

 

[Thunderchild]

if the filament is cooler and has less resistance it would let more current through !

that was my thought with DC it would stay at constant temp and resistance

 

[audioguru]

Thunderchild,
A 230VAC sine-wave has 650V peak-to-peak. The filament in a light bulb heats and cools much slower than the 100Hz pulses so the 230VAC average power is exactly the same as 230VDC.

 

[Nigel Goodwin]

Another disadvantage of DC is the large surge EVERY time you turn it on, with AC you've got a chance of it softstarting from zero, or somewhere between there and peak voltage. With DC it will always start at the full DC voltage.

 

[Thunderchild]

true as well

 

[k7elp60]

I have been running some 12V bulbs on DC as reading lights. The existing bulbs have been in the socket for over 5 years. They are used almost every evening. I solved the surge current problem with a circuit the uses NTC thermistors. The thermistor is in series with the bulb when the power is first turned on, but in about 5 seconds it is shorted out with a power mosfet. I used some RV light fixtures and added the circuitry to the fixture.

 

[audioguru]

Another disadvantage of DC is the large surge EVERY time you turn it on, with AC you've got a chance of it softstarting from zero, or somewhere between there and peak voltage. With DC it will always start at the full DC voltage.

I have never used DC for household bulbs but on AC they burn out always when turned on. Do you think DC would kill them sooner?

I think they have a huge current surge when cold and the thermal delay of their warm-up is many cycles of the AC. So the huge amount of power at turn on kills them when they are old.

 

[Thunderchild]

thats true as well

 

[pfofit]

I've got several trilite lamps and I got tried of throwing away expensive half dead or rather third or 2/3 thirds dead tri-lite bulbs.

I wanted a dimming feature so I soldered a standard 1n4007 diode across the two contacts at the bottom of socket, Use regular bulb up to 100 W and I now have> off, half wave, full AC,full AC off . etc

Great dimming feature and no flicker, seems the persistence in the filament holds brightness level and da wife doesn't complain or even know for that matter, so passes usability test.

Not sure how Non north american tri lights work or even if they exist or if half waving 50 Hz will be noticeable, but mine have been in use for many, many years and bulbs never get changed as it is dim mode most of the time except when turning off. One is on a wall switch outlet, so it hardly ever gets a full blast

cheers

 

[Bob Scott]

I've got several trilite lamps and I got tried of throwing away expensive half dead or rather third or 2/3 thirds dead tri-lite bulbs.

I also became annoyed at frequent and expensive trilight failure in a fair of living room lamps. While I was down in California I picked up a table lamp dimmer from Ace hardware. It's the regular triac wall type phase control dimmer but in its own small box for table lamps. It has an corded AC plug and corded AC jack. So I replaced the 2 trilight bulbs with cheaper 200 watt bulbs.

I found it odd, but running the bulbs less than full power with the dimmer does not seem to make them last any longer. ??

Bob

 

[RODALCO]

I use standard 60, 75 and 100 Watt lightbulbs on the outside of my house which are controlled via an astronomical timeclock.
For the last 20 years or so i use a 1N4007 diode in series with each lamp.
The lamps last up to 2 years ± 9000 hours.
A hour meter is connected to the timeclock for monitoring of lamp burning hours, and series CT's with LED indicators and alarm are on each circuit, will tell me if a lamp fails.
A little flicker is noticeable in the filament and some reduction in light output because 0.707 x power is available.
For the purpose it is fine, especially for two lamps which are on the high side of the house and difficult ot replace.

We talk 230 volts 50 Hz mains here.

 

[audioguru]

A little flicker is noticeable in the filament and some reduction in light output because 0.707 x power is available.

Actually, the voltage is half for half the total time.
The current is also nearly half for half the total time.
Therefore the power is nearly 0.25 isn't it? Much less light than without the diode. Also the colour of the light is orangish instead of white.

I use compact fluorescent light bulbs that use 0.25 the amount of power than incandescent ones but have the same amount of very white light, operate for 10,000 hours and are much cooler.

 

[things]

operate for 10,000 hours.

i have this desk lamp, and i had a incandescent bulb in it, but then it died. so i got one of those flouro ones and it killed that one too. that lamp has killed every bulb that has been put into it. When i took the flouro bulb out, it had a little brown burn mark on the side. What is going on with this lamp????? there isn't anything in that lamps circuitry except for a switch, wires and the bulb. How could that blow 3 bulbs in a row?????

 

[audioguru]

Heat rises.
The lighted part of a light bulb gets very hot.
So if the lighted part of the bulb is downward in your desk lamp then the electronic parts in the base are being cooked. Then they won't last long.

Many incandescent light bulbs have a warning on the package with a symbol of the lightbulb pointing down and a red line through it. Don't do dat.

 

[Thunderchild]

well actually 0.5 times the power i think audio guru because the power is off half of the timea 100 watts bulb will use 100 watts half the amount of time, i think it does not quite work out like averaging it, if it were constant 0.5 X V then yes

 

[RODALCO]

0.7 x 0.7 = 0.5 x Voltage.
These bulbs are in open porcelain baijonet sockets. the fluro's don't like these exposed conditions.