While looking at the web with respect to this problem I found this site:

http://www.electronicsfaq.com/2013/11/measuring-hot-resistance-and-cold.html which produced some baseline data about the cold resistances and hot resistances of some 240 V bulbs.

http://www.analog-innovations.com/ has a spice model for incandescent lamps, which of course can be modified to change the power level. Jim Thompson PE, a frequent contributor in the Science Electronics Design NNTP group designed that model.

I am sure that the question here, intended to use the "hot resistance" of the bulbs, as calculated, but I suspect that once one does the calculations, it will come close to the theoretical, unless of course we wish to disregard KVL and KCL.

Even knowing the lumens per watt at 60, 80, and 100 are between 16 and 17, once the bulbs are in series, I suspect the lumens per watt would be reduced to the values normally associated with the lower powers and not their normal operating lumens per watt, as the "heating" power has been reduced as well.

This brings us back to the lamp consuming the most power in the series string as the one being the brightest. That would be the 60 Watt lamp.

 

While that may be the case, I suspect that the homework problem was intended to use a far simpler model, probably one in which the resistance of the bulb filaments is completely temperature independent. Not realistic, but I don't think that was the point of the problem.

Hi,

I have to agree that it may be a simpler exercise but i just could not resist the temptation to use the equations normally associated with light bulbs under static operating conditions to see what it would show. It is just too interesting and the fact that the middle bulb came out the winner makes it even more interesting to me because non of us guessed that because we automatically went with what we thought was the most extreme based on either resistance or voltage, when really it's non linear so we get an unexpected result.

I also thought a little more about the time model where we dont assume that the specific heat capacities of all the filaments are negligible. I think what could happen is all the bulbs would get at least the same current, and so their filaments would still heat up even if not right away, and this would lead to the more static case. Unfortunately this is just a guess and we found that intuitive guesses are not reliable, so a better model of the bulb would be needed to answer this question, unless of course somebody wanted to try this at home (it's not that difficult to hook up three bulbs). I might try this but i dont think i have an incandescent bulb rated for 100 watts around anymore since they went extinct

 

Hi,

I have to agree that it may be a simpler exercise but i just could not resist the temptation to use the equations normally associated with light bulbs under static operating conditions to see what it would show. It is just too interesting and the fact that the middle bulb came out the winner makes it even more interesting to me because non of us guessed that because we automatically went with what we thought was the most extreme based on either resistance or voltage, when really it's non linear so we get an unexpected result.

I also thought a little more about the time model where we dont assume that the specific heat capacities of all the filaments are negligible. I think what could happen is all the bulbs would get at least the same current, and so their filaments would still heat up even if not right away, and this would lead to the more static case. Unfortunately this is just a guess and we found that intuitive guesses are not reliable, so a better model of the bulb would be needed to answer this question, unless of course somebody wanted to try this at home (it's not that difficult to hook up three bulbs). I might try this but i dont think i have an incandescent bulb rated for 100 watts around anymore since they went extinct

I agree. I actually went looking for a site that I ran across a couple months ago that tabulated some resistivity vs. temperature data for tungsten to see what the results would be if we just looked at power dissipation alone. But I haven't been able to find the site again.

 

While looking at the web with respect to this problem I found this site:

http://www.electronicsfaq.com/2013/11/measuring-hot-resistance-and-cold.html which produced some baseline data about the cold resistances and hot resistances of some 240 V bulbs.

http://www.analog-innovations.com/ has a spice model for incandescent lamps, which of course can be modified to change the power level. Jim Thompson PE, a frequent contributor in the Science Electronics Design NNTP group designed that model.

I am sure that the question here, intended to use the "hot resistance" of the bulbs, as calculated, but I suspect that once one does the calculations, it will come close to the theoretical, unless of course we wish to disregard KVL and KCL.

Even knowing the lumens per watt at 60, 80, and 100 are between 16 and 17, once the bulbs are in series, I suspect the lumens per watt would be reduced to the values normally associated with the lower powers and not their normal operating lumens per watt, as the "heating" power has been reduced as well.

This brings us back to the lamp consuming the most power in the series string as the one being the brightest. That would be the 60 Watt lamp.

Hi there Joe,

Using the cube root law for bulbs the 60 watt bulb in your results would come out the brightest, but what model did you use for the bulbs?
Also, is this the same model you talked about in your post above at "analog-innovations.com" ?
Also, where is the bulb model you quoted as having been developed by "analog-innovations" or whatever?

I ask these questions because it looks like you used the 'hot filament' model of the bulb, which we may still really want to know about but we might also want to know about the more realistic model. As WBHan pointed out we may end up using the hot filament model for this particular problem, but i think it is still interesting to look deeper.

I'd like to take a look at this model too and see what i can find out (not the hot filament one of course).

What might happen is when the circuit is first turned on, the 60 watt bulb heats up first and steals most of the voltage, so the other two dont heat up as much. But after a little longer i think they would still heat up more and more, and once the circuit reaches thermal steady state we end up with the static solution anyway. I think this is true because the temperature rises monotonically with current, and so the resistance does too, even though non linear. But we all know that non linear circuits are not as intuitive as linear ones so a good model would be great, one that considers the heating of the filament over time.
I also realize that unfortunately this may be hard to test in real life, because we'd need a high speed camera to record the brightness of the bulbs as they heat up over a few milliseconds to maybe tens or a few hundreds of milliseconds, and the results may not be ideal because it may be hard to match the bulbs for similar general qualities.

The slightly comical side to this is that they should no longer be using incandescent bulbs

 

Al,

I think it would hold true at the lower power incandescent as well. It would be interesting to try as the lower incandescent still exist.

Did the whole world outlaw incandescent lamps above a certain power?

The model is on the analog-innovation site.

The efficiency (lumens per watt) of the incandescent can make the 80 W bulb the winner in this scenario and I suspect it could even make the 100 W the "brightest" as well provided it maintained the highest lumens per watt and the others were at the lower end of the scale. I suspect the question is ambiguous, because the answer they most likely desired, was the most power consumed in the series string.

 

I actually went looking for a site that I ran across a couple months ago that tabulated some resistivity vs. temperature data for tungsten to see what the results would be if we just looked at power dissipation alone.

There is a chart in the NIST pages I've attached and then there is this website http://hypertextbook.com/facts/2004/DeannaStewart.shtml

 

Hello,

From the dutch wiki (google translated) :

Prohibition
In the European Union is selling many types of traditional light bulbs from September 1, 2012 banned from energy considerations. [2] Similar plans exist for the state of California in America. In the Netherlands, most types of bulbs can no longer be placed on the market by September 1, 2012, but that existing stocks may be sold. On 1 September 2009 the production of many kinds were 100, 75 and 60 watt bulbs already banned. [3] As of September 1, 2016 there should be no single bulb sold more of most lamp types in the European Union.

There is also a nice table to compare the incadent with led and halogen.

Bertus

 

When i get home ill post the minimums. The lumen charts we see are as bright as xxx watts, but the actual power is less... i.e. 100 watt brightness for a maximum of 73 watts. The question as asked must be is as old as edison ... So we are not reallly doing a good job of comparasion.

The law specifies the min lumens and max power consumption.

On edit: Fixed texting problems caused by fat fingers on a smart phone.

 

From NEMA SUMMARY AND ANALYSIS OF THE ENERGY INDEPENDENCE AND SECURITY ACT OF 2007 (file attached) ...

 

Hi again,

I didnt see it on their site. They dont have a search either.
I am hoping that this model includes light output characteristics as well as the electrical characteristics. I know some models that dont have this and i think we need that too to be sure.

 

[url]http://www.analog-innovations.com/[/URL]

 

Hi Joe,

Thanks for posting the model.

What else i did was looked up a small bulb i did a curve trace on a long long time ago. I logged the current and voltage for 22 points from 0.102 volts to 1.504 volts, and used that to form a fairly good curve fit equation that relates V to I. I then used this to create the three bulb models, then calculated the power and then the light output for each one.
Note these were 1.5v bulbs nothing near 240v like we had been using.

The results were totally different. The smaller, lower power bulb, had produced the most light output. This might be equivalent to the 60 watt bulb as before, but lower power this time.

It's hard to explain this difference, except that the curve of the bulbs happens to be different so we see different results for the lower power bulbs. Note this is using the same basic technique as before, estimating the light output using the same relationships.

I guess we could try that new model too next.

 

I haven't ever seen 80 watt incandescent bulbs, but two 40 watt bulbs in parallel can stand in for an 80 watt bulb.

Connecting a 60w, 80w and 100w bulb (all rated for 120 VAC) in series and energized with a 230 volt variac, I get the following results:

Turning up the variac from zero, the 60 watt bulb is substantially brighter at all applied voltages. Because of this, I monitored the voltage across the 60 watt bulb as I turned up the variac to make sure it didn't experience an overvoltage.

Turning up the variac until the voltage across the 60 watt bulb was 120 VAC, the final score was:

Total voltage across the series string = 227 VAC.
Total current through the string = .493 A

Voltage across            Power dissipation
   each bulb                  each bulb
60w  = 120 VAC               59.2 watts
80w  = 64.3 VAC              31.7 watts
100w = 42.7 VAC              21.1 watts

 

For what it's worth, here is the V-I characteristic of the 60 watt bulb I used:

Applied voltage       current, amps
10                        .153
20                        .200
30                        .242
40                        .279
50                        .313
60                        .342
70                        .372
80                        .398
90                        .424
100                       .448
110                       .472
120                       .494

 

Interesting results.

It also reminds us of the associated problem that is sometimes asked, when placing three 120 V rated bulbs in series, what is the maximum voltage you can apply to that series string. Some will immediately JUMP on the 360 V answer.