wattage

[Big_Spark]

Its "Christmas", obviously you two have a disagrrement, but moaning about who said what does not help any one on this forum.

You two are some of the most influential posters with regard to electrics, if you do not make up, or agree to dissagrre i will remove the post (besides you two swear too much)

I think that is a bit extreme..yes we are not seeing eye to eye..but actually this thread is going somewhere now..see my last post...

 

[moderator]

I have to admit, I was typing as you were, and I did not see your post.

but please boys no more arguments

 

[Big_Spark]

I have to admit, I was typing as you were, and I did not see your post.

but please boys no more arguments

Can we stamp out feet a bit.......

OK..I'll get my coat

 

[moderator]

I have to admit, I was typing as you were, and I did not see your post.

but please boys no more arguments

Can we stamp out feet a bit.......

OK..I'll get my coat

only if you do it quietly

 

[Adam_151]

The problem with big spark's experiment is that the filament cools a lot in the 4 seconds it takes him to take it out of the fitting and measure it.

if you switch a lamp off and watch how long to takes to stop radiating light, that'll give you an idea of how fast it cools, I reckon the cooling must be expontial of some sort, its obviously cooling much slower on the table than it was the moment the circuit was broken.

if someone wants to put their ammerter in series with a table lamp or something, then along with a voltage reading of the mains supply, we can get the hot resistance of the filament, I would do it, but not only is my multimeter an uncalibrated cheapo thing, its also in the garage and its now the early hours.... maybe tommorow

 

[Spark123]

I was under the impression it would cool exponentially too, (negative exponential)

 

[ban-all-sheds]

So, Ms Moderator-with-a-delete-button, am I allowed to make a post pointing out the obvious and fairly fundamental flaw in the experiment that B_S did?

EDIT PS.

OK - too late to ask for permission, it's already been pointed out.

As soon as power is removed, the lamp stops glowing. I have no idea what the temperature would have dropped to after 4 seconds, but a very rough and ready test just now shows a 60W R63 stopping all visible radiation in less than one second, which means that it's already dropped to less than 500°C.

Another way to intuitively show that that is right is to look at the reverse process of heating the filament. Does it take a noticeable amount of time to reach full brightness, or does it happen in a space of time so short that it cannot be detected by human observation?

 

[Big_Spark]

After I did the experiment and posted I actually started to think about the cooling as I realised that it must cool a lot faster initially..however the thing that has me intrigued is the fact that both lamps..the 40W RO40 and the standard GLS 100W have the same resistance ratio between hot and cold..Now I understand that at cold this is likely to be the case, and at operating temperature this will likely also be true..but would they cool at the same rate to keep this ratio? The are different, it is obvious to one and all that the 100W filament will be different to the 40W filament, otherwise they would have the same resistance..The 40W filament must be thicker in order to have the higher resistance, thus it should cool slower than the 100W filament..BUT the question is whether the difference in their structural matrices is sufficient for me to be able to spot that temperature and thus resistance difference?

Well I am not giving up on it..I am now hunting out more information to find out the exact rate of cooling of tungsten filaments and their respective operational temperatures..

Once I have it I'll post it here...

 

[Big_Spark]

Initially I have found this in a .pdf document..

Operating Temperature
Minimum bulb temperature is about 200 degrees Centigrade as required by the halogen-tungsten cycle.
Maximum temperature applies to the pinch. If the molybdenum foils reach too high a temperature, they will oxidize, and the greater volume of the oxidant will force open the glass. By international agreement:



LIFE MAXIMUM PINCH TEMPERATURE
------- -------------------------
< 15 hours 450 degrees Centigrade
15-300 hours 400 degrees Centigrade
> 300 hours 350 degrees Centigrade

And this bit further down..

Graph 25 on page 25 of Tungsten Halogen Low Voltage Lamps Photo Optics can be used to estimate the color temperature of high-load (high luminous efficacy and tungsten near the melting point), low-voltage lamps for which only the luminous efficacy is known. As a rule of thumb, around 3000 degrees Kelvin:

At 30 lm/W the color temperature is 3330 degrees Kelvin.

With every 3 lm/W the color temperature changes by 100 degrees Kelvin. (Higher efficacy implies higher color temperature.) This color temperature should not be confused with the physical temperature of the filament or glass bulb, which will be in the region of 250ºC to 450ºC depending on the intended use and expected life of the lamp.

And

At the highest practical temperatures, peak radiant flux is at about 850 nm (visible ends at 780).

20.0% visible light
0.3% ultraviolet
79.7% infrared (heat)

Although searching further makes me think that the above may have some errors in it as I have found this on the Osram site..although this referrs specifically to Tungsten-Halogen Lamps and NOT GLS lamps..

At the filament where the temperature exceeds 2500°C, the tungsten halide dissociates, the tungsten is deposited on the filament, and

 

[Big_Spark]

And from another source I have found this..The bit I have made bold tells the story of the filament temperature..so there was most certainly an error in the original article I read..still looking for the cooling coeficient of the filaments though..

Gas filled lamps produce light from anincandescent filament operated in an inert gasatmosphere.The addition of the inert gassuppresses the evaporation of the tungstenfilament, which increases the lifetime of the lamp orallows higher temperature operation for the samelife.The normal gases used are Nitrogen, Argon,Krypton and Xenon.The cost rises dramatically asthe rarer gases are used, particularly for Xenon,due to their very low natural abundance.Theadvantage of the higher atomic weight gases isthey suppress the evaporation of the tungstenfilament more effectively than the lower weightgases.This allows the filament of gas filled lamps to be run at temperatures up to 3,200 degreesKelvin and achieve reasonable life times.The light from these lamps has a high blue content giving thelight a pure white appearance.Gas-filled lamps require more power to achieve thesame filament temperature than vacuum lamps.The surrounding gas cools the filament whilesuppressing evaporation, and reducing themigration of evaporated tungsten to the wall of thelamp.The higher operating temperature of gas-filledlamps produce more light output per watt of inputpower, which justifies their use in criticalapplications

 

[Big_Spark]

Did a little further experimentation..

Current drawn by a single RO40 40W reflector lamp = 0.133A which equates to a HOT resistance of 1786.466 Ohms which give a hot/cold resistance ratio of 16.8/1

Now the current drawn by the 100W GLS lamp is 0.35A which correspends to a HOT resistance of 678.85 Ohms which gives us a hot/cold ratio of 21.75/1

I have also discovered that the temperature coeficient of the filament follows the inverse square rule when cooling.

Basically for every doubling of time in seconds, the filament reduces temperature 4 fold..for every 4 seconds it drops 16 fold etc etc..

But this is also dependent on the gases used in the bulb. Heavier Gases, such as Krypton and Xenon, allow the heat to be dissipated faster and more efficiently that lighter gases such as Nitrogen and Argon.

I discovered a formula for calculating the exact temperature drop of a given lamp..but it is very complicated and requires the user to know the physical properties of the gases in the lamp, as they are a complex mix in some cases and this alters their properties when dealing with heat. It also takes into account eh vapourisation temperatures of the filament, the Molybdenum in the structure of the lamp and the gases themselves, as well as the actual operating pressure in the vessel..which is anything from 7 to 11 atmospheres. On top of this it accounts for the heat dissipation properties of the glass bulb of the lamp which will vary depending on the glass thickness and its method of manufacture and the material used to construct it....this last part is the most difficult to comeby as the exact ingredient ratios of given glass bulbs is uniques to each series of lamps and unique to each manufacturer, and they apparently guard this mix as if an official secret as it effects the life and efficacy of the lamp...

 

[Stoday]

A long time ago, when I was learning "O" level physics, we measured the hot resistance of a lit lamp by measuring the current through and the voltage over it. From which we could calculate the power without all the hoo-ha that Bog_Spark goes into.

One of the fundameental laws of radiation is Stephan's Law which says that radiated energy is proportional to the forth power of the temperature difference. That's a far steeper curve than the exponential. That's why Big_Spark's estimate was so far out - he initially assumed linear, then agreed with someone who suggested exponential.

Moderator - please don't delete this thread. It's interesting and much more fun than most.

 

[Big_Spark]

Stoday, why do you feel the need to attack...You state that you did exactly what I have done..so your a fool and a muppet as you contradict yourself..

Yes I thought linear..but the INVERSE SQUARE RULE is NOT Exponential..

And from what I have been reading this day I have found the calculations for the temperature/resistance curve of a tungsten filament lamp is extremely variable due to other factors and the calculations are far from simple..as I explained above..

I have hunted for a standard calculation that would imply some relationship between temperature, material and time..but there isn't one unfortunately..

Now Stoday, instead of attacking and insulting, why don't you do something that actually adds to this discussion......or are you too stupid to understanbd what is being discussed so you simply try to repeat comments made by others??? Come on, make me smile and prove me wrong about how I think of you..