190129-2407 EST
Dennis:
All of this should have been covered in high school physics class.
You need to do some Internet search on the subject, and some valid experiments.
You need a Variac, adequate meters (instruments), a tungsten filament bulb, if possible, an Edison carbon filament bulb, an Ohmite power resistor, a hot plate, and a 1500 W space heater that does not include a fan, lower power would be OK. All of these loads can be considered a good resistance once their temperature stabilizes. Then play.
Randomly selected tungsten filament bulbs of the same voltage, and wattage rating are quite close to one another in their value.
A random 120 V 100 W tungsten bulb read 9.7 ohms at room temperature, 80 F, with a Fluke 27, and its leads directly on the bulb. I was getting up 15 ohms when the bulb was in a socket with a switch.
Using a Variac and a Kill-A-Watt EZ I read ---
120.3 V, 0.82 A, 99.1 W, calculated from V and I P = 98.6 W, and R = 147 ohms.
090.2 V, 0.71 A, 64.4 W, calculated from V and I P = 64.0 W, and R = 127 ohms.
Room temperature 9.7 ohms. Normal brightness to room temperature has a resistance ratio of 147/9.7 = 15.2 to 1.
Lower voltages and Kill-A-Watt may not give good results. But you already see the change in resistance.
From the Internet see ---
https://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity
Go to the table of thermal coefficient for various materials.
K = 0.00404 for copper
K = 0.0045 for tungsten
K = 0.0004 for Nichrome
K = -.0005 for carbon --- Edison's lamp
K = 0.000008 for Constantan
K = 0.000002 for Manganin
You do some searching for the equation that includes K and how to use it.
In searching for the Invar coefficient and looking at Wiki at
https://en.wikipedia.org/wiki/Temperature_coefficient#Electrical_resistance
I did not find what I wanted, but it is interesting that a person about 3 block away from me popped up.
This was James Duderstadt.
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