Light Bulb Experiment: Some Observations

I've connected a simple incandescent lightbulb to a PASCO 850 Interface setup which I'm using to provide power and also to measure current and voltage outputs, as well as a voltage sensor for the lightbulb itself. Additionally, I've connected a High Intensity Light Sensor to the PASCO 850 Interface to measure the light's intensity while I am doing this. The image below shows the basic signal generator information along with the Voltage sensor reading as a function of current output (data from the light sensor isn't shown).

I want to highlight a few points here, and maybe (no promises) add some follow-up posts.

First, note my general set-up: my voltage output is a positive ramp with an amplitude of 2.4 V, although there is some internal resistance in the wires and hence the voltage drop across the bulb itself is more like 2.3 V. I have a voltage limit of 2.5 volts--this is the limit specified by the light bulb which I am using, although with my ramp settings, I should not ever see this voltage output. The Ramp repeats itself every 2 seconds (0.5 Hz frequency).

There appears to be two approximately linear regimes for this bulb, with a pair of nonlinear transient regimes. There is also a "line" from "top" to "bottom", but this is an artifact of the ramp's repeating itself. The first "nonlinear" part of the graph is when the bulb is first turned on, and thus the filament rapidly heats up and its resistance increases. This region is the curving "tail" to the lower right of the higher linear region, and I will set this aside for now (it can be easily selected around by introducing a short delay to the data collection from when the signal is turned on).

The two "linear" regimes represent when the voltage is too low for the bulb to glow, < ~0.25 V, and again when the voltage is strong enough for the entire filament to be glowing, > ~0.9 V. The "S"-shaped transient region connecting the two is when the filament begins to glow, during which the slope (and hence resistance) actually increases somewhat, compared even to "hot" vs "cold" resistance (everything outside of the "tail" is basically "hot" resistance, albeit not steady state).

For what it is worth, the "resistance" (measured by taking the slope of the linear portion) is about 15.1 Ω for the upper "on" region and about 2.2 Ω for the lower region with these settings. Two other notes here: these values change somewhat if I change the ramp frequency, and also neither "linear" region is actually entirely linear. To the first note, I can offer this graph taken at 0.1 Hz:

The slopes are now 14.9 Ω and 1.76 Ω, respectively. These differences, especially the former, may seem small, but they are repeatable.

And for the second point, I will want to look at in a future post. Hint: it involves turning off the ramp and looking at just a DC signal.