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+--- Thread: Planck and the light sensor (/showthread.php?tid=1533)
Planck and the light sensor - Erik Josefsson - 03-21-2022
Hello,
I'm planing to buy infra red equipment (maybe FLIR C5 or RSpec Explorer, links below) to measure and compare the temperature of resistors and light bulbs at the same time as students measure voltage and current. Maybe even determine the melting point of tungsten...
Of course I'd like to add phyphox' light sensor to the mix.
For example, did anyone try the sensor with a infrared 10-nm filter?
https://opticalfiltershop.com/shop/specialty-filters/lidar/visible-bandpass-filter-670nm-fwhm-10nm/
Grateful for links and/or other tips.
Best regards.
//Erik
https://www.sagitta.se/artikel/matutrustning/temperatur/varmekamera-flir-c5
https://www.alega.se/sv/articles/2.3018.37375/digitalspektrometer-rspec-explorer
RE: Planck and the light sensor - solid - 03-21-2022
Hi Erik
I did not measure the light with filters but I measured the polarized light passing through a polarizer (Malus law) and I saw that telephon sensor cuts low intensity light. To the contrary SensorTag light sensor measures the light intensity correctly.
https://phyphox.org/forums/showthread.php?tid=1221
RE: Planck and the light sensor - Erik Josefsson - 03-21-2022
(03-21-2022, 08:14 AM)solid Wrote: Hi Erik
I did not measure the light with filters but I measured the polarized light passing through a polarizer (Malus law) and I saw that telephon sensor cuts low intensity light. To the contrary SensorTag light sensor measures the light intensity correctly.
https://phyphox.org/forums/showthread.php?tid=1221
Hi solid, thanks will look soon.
I guess the sensor is "calibrated" according to the "Luminous efficiency function"
https://en.wikipedia.org/wiki/Luminous_efficiency_function
and that cuts red light dramatically.
But if you pick a 10 nm infrared slice of what comes trough as a signal, then you could maybe get approximate values of the temperature?
This is great: https://www.geogebra.org/m/rYP7WA3h
I attach a picture of the planck curve at the tungsten melting point.
Best regards.
//Erik
RE: Planck and the light sensor - solid - 03-21-2022
You need at least 2 filters and a callibration procedure in order to determine the temperature. A nice idea of an experiment. I should try it with my interference filters.
RE: Planck and the light sensor - Erik Josefsson - 03-21-2022
(03-21-2022, 02:16 PM)solid Wrote: You need at least 2 filters and a callibration procedure in order to determine the temperature. A nice idea of an experiment. I should try it with my interference filters.
Thank you!
The light sensor should pick up the light from the light bulb nicely as soon as it starts to glow, and, therefore, you could maybe "force" it to just measure intensity of one wavelength ±5 nm (as the red filter I found does). Before "glow temepratures" you'd have to rely on the infra red camera.
The intensity of that wavelength could then perhaps be used to find the temperature of the tungsten filament, even if the λ-max at each temperature will become shorter as temperature increases (Wien's law).
As you'd have U*I for every light sensor value (and at low temperatures for every heat camera measurement) it should be possible to figure out the area of the emitting tungsten filament, no?
Sorry, no measurements yet, just thinking loud...
Best regards.
//Erik
RE: Planck and the light sensor - Jens Noriʇzsɔɥ - 03-21-2022
Please note that the “quality” (including rate and resolution) heavily varies between smartphones and infrared might get filtered (for some time, it was not possible to see the light of a remote on iPhones, for instance – however, there is no interface for the light sensor anyway: https://phyphox.org/faq/#faqIosLight)
RE: Planck and the light sensor - Erik Josefsson - 03-26-2022
(03-21-2022, 09:10 PM)Jens Noritzsch Wrote: Please note that the “quality” (including rate and resolution) heavily varies between smartphones and infrared might get filtered (for some time, it was not possible to see the light of a remote on iPhones, for instance – however, there is no interface for the light sensor anyway: https://phyphox.org/faq/#faqIosLight)
Yes, you would have to know what sensor your phone has. In my case GT-I9300, but thanks to the excellent sensor database I can find out more about what the sensor can and cannot do: https://phyphox.org/sensordb/
Name
CM36651 Light Sensor
Vendor
Capella Microsystems
Range
121240 lx
Resolution
1.0 lx
The question here is whether that sensor can add information and/or measure data in the educational context of heat radiation and planck curves.
Clearly the CM36651 Light Sensor will "see" a fully shining 3.5 V small light bulb very well, but what if the light was filtered so that only 670 ± 5 nm comes through?
And if so, would that signal say anything meaningful in relation to the light bulb power (P=U*I)?
According to this fine graph just 0.5% of the total radiation power would come from 670 ± 5 nm at T=3000 K:
https://www.geogebra.org/m/EtCNHst7
and even less would show as signal if the sensor indeed uses the Luminous efficiency function.
But it would be nice to know :-)
Best regards.
//Erik
RE: Planck and the light sensor - Jens Noriʇzsɔɥ - 03-29-2022
My gut feeling is: IDK…
I suppose/fear some heavy technical specs digging of the light sensor is required.
RE: Planck and the light sensor - Erik Josefsson - 03-30-2022
(03-29-2022, 05:42 PM)Jens Noritzsch Wrote: My gut feeling is: IDK…
That would surely help avoid dead ends! I have yet to master the FLIR camera. It does not take the pictures I expected.
Best regards.
//Erik