[hamdani yusuf (OP)]

We get a bunch of thermometers.
It would be a dumb choice but, just to make the point, we can use a mercury thermometer, an alcohol thermometer a gallium thermometer, a water thermometer  and a hexane thermometer.

Liquid filled thermometers like mercury and alcohol typically use glass for interface with measured object, which was chosen to allow visual observation of the temperature driven expansion of the liquids. While electronic thermometer like RTD and thermocouple use metal alloys for interface. They have different selectiveness in radiation frequencies to be accommodated in the temperature measurement. But those contact temperatures rely on heat conductance between the measured objects and the thermometer interface. Other effects like electromagnetic radiation from the measured object or its environment are considered noise. But this noise can be significant in some situations. Being unaware of these effects can lead to erroneous measurement values.

[alancalverd]

In clear air, what's the typical range of microwave radar?

Depends on the radiated peak power, and is only limited by the horizon.

The problem with using the em radiation spectrum to measure the temperature of a distant target is selective absorption by the intervening air, which distorts the received spectrum - particularly if the target is air itself! So I'd prefer to concentrate on  the low-frequency (sub-GHz) end of the spectrum. 

This is a bit of an angels-on-pinheads argument anyway. Common sense says that the air close to the spinning magnet will be  in thermal equilibrium with the magnet surface, so we can use the magnet as the  target for a conventional thermistor pyrometer - much simpler and good to about +/-0.5K.

[Bored chemist]

Depends on the radiated peak power, and is only limited by the horizon.

Pick one.
But...
"Common sense says that the air close to the spinning magnet will be  in thermal equilibrium with the magnet surface"
Not really; but the problem lies with the definition of the problem.
If the magnet is spinning then viscous dag will heat the air near to it.
And then it won't be at equilibrium any more.

[Bored chemist]

Being unaware of these effects can lead to erroneous measurement values.

And the guy who can tell you about 5 different sorts of liquid in glass thermometers is almost certainly not "unaware of these effects".
But you seem un\aware of the fact that a spinning magnet in air will heat the air, thus disturbing the equilibrium.
And, if it's not at equilibrium, it doesn't have a properly defined temperature.

What point did you think you were making, and to whom?

[hamdani yusuf (OP)]

But you seem un\aware of the fact that a spinning magnet in air will heat the air, thus disturbing the equilibrium.

You seem to be unaware that as an example, I put the spinning magnet inside a vacuum glass box. There will be no friction between the air and the spinning magnet. But the spinning magnet can still generate heat in nearby metals by inducing Eddy current.

[hamdani yusuf (OP)]

And, if it's not at equilibrium, it doesn't have a properly defined temperature.

Does the surface of the sun have a properly defined temperature?
Does the corona of the sun have a properly defined temperature?

[Bored chemist]

But you seem un\aware of the fact that a spinning magnet in air will heat the air, thus disturbing the equilibrium.

You seem to be unaware that as an example, I put the spinning magnet inside a vacuum glass box. There will be no friction between the air and the spinning magnet. But the spinning magnet can still generate heat in nearby metals by inducing Eddy current.

I'm unaware of many things that you just decided to make up. Mindreading isn't my forte.
You should have mentioned it.


You do know that oxygen is paramagnetic, don't you?

And, if it's not at equilibrium, it doesn't have a properly defined temperature.

Does the surface of the sun have a properly defined temperature?
Does the corona of the sun have a properly defined temperature?

Fairly well defined. But, in principle, your spinning magnet warms it up a bit.
Why do you ask?

[alancalverd]

If the magnet is spinning then viscous dag will heat the air near to it.
And then it won't be at equilibrium any more.

We tend to consider the boundary layer a stationary in laminar viscous flow. And it would be a pity if Joule's determination of the mechanical equivalent of heat by stirring water was seriously wrong - his result was within 0.75% of the current value.

[Bored chemist]

If the magnet is spinning then viscous dag will heat the air near to it.
And then it won't be at equilibrium any more.

We tend to consider the boundary layer a stationary in laminar viscous flow. And it would be a pity if Joule's determination of the mechanical equivalent of heat by stirring water was seriously wrong - his result was within 0.75% of the current value.

Joule measured the rate of rise of temperature.
Funny looking eqm that's getting hotter with time.

[alancalverd]

I spent several years working on "dynamic equilibrium" calorimeters for measuring ionising radiation dose rates. Long story but it was a cunning way of measuring millidegree temperature changes to better than 0.1% precision.

The classic Callendar and Barnes continuous flow water calorimeter uses a similar principle.

[hamdani yusuf (OP)]

But, in principle, your spinning magnet warms it up a bit.

The effects are much less than Eddy current generated in metals, thus doesn't significantly change the temperature measurement.

[hamdani yusuf (OP)]

I started this thread in new theory section because I found that currently available explanations are not satisfactory and contains many caveats. I wondered if it can be improved.

https://en.m.wikipedia.org/wiki/Temperature
Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making up a substance.
...
When two systems in thermal contact are at the same temperature no heat transfers between them. When a temperature difference does exist heat flows spontaneously from the warmer system to the colder system until they are in thermal equilibrium. Such heat transfer occurs by conduction or by thermal radiation.[45][46][47][48][49][50][51][52]

Experimental physicists, for example Galileo and Newton,[53] found that there are indefinitely many empirical temperature scales. Nevertheless, the zeroth law of thermodynamics says that they all measure the same quality. This means that for a body in its own state of internal thermodynamic equilibrium, every correctly calibrated thermometer, of whatever kind, that measures the temperature of the body, records one and the same temperature. For a body that is not in its own state of internal thermodynamic equilibrium, different thermometers can record different temperatures, depending respectively on the mechanisms of operation of the thermometers.

From the underlined statement, we need to define what counts as thermal contact. Also, what counts as heat transfer and thermal equilibrium.

For anyone who wonders why I started this thread, or already forget it. I discussed this with ChatGPT.
What's the common temperature of incandescent lamps?

The common temperature of incandescent lamps typically refers to their color temperature, which is measured in Kelvin (K). It usually falls in the range of:

2,700 K to 3,000 K: This gives off a warm white or yellowish light, resembling traditional incandescent lighting.

3,200 K: Often used in photography and studio lighting, providing a slightly cooler white light.


In terms of operating temperature, the filament inside an incandescent lamp can reach 2,500 to 3,000?C (4,500 to 5,400?F) when glowing. The surface of the bulb itself is much cooler but still quite hot, often around 150 to 250?C (300 to 480?F) depending on the wattage.

Note that objects heated by radiation from incandescent lamps can have higher temperature than the glass surface of the lamps. This pose question about thermal contact. Is exchange of kinetic energy through radiation counted as thermal contact?

[hamdani yusuf (OP)]

Is their spectrum similar to black body radiation?

Yes, the spectrum of incandescent lamps is very similar to black body radiation because the light is produced by heating a tungsten filament to high temperatures.

Here?s how they compare:

1. Black Body Radiation:

A black body is an idealized physical body that absorbs all incident radiation and emits a spectrum of radiation based solely on its temperature.

Its spectrum is continuous, with a peak wavelength determined by the Planck radiation law.



2. Incandescent Lamps:

The tungsten filament closely approximates a black body because it emits light due to being heated to 2,500?3,000 K.

The spectrum is continuous, covering visible light and extending into the infrared (IR), which is why these lamps are inefficient as a significant portion of energy is emitted as heat (IR radiation).




However, the spectrum of an incandescent lamp is not a perfect black body due to:

Material properties: The tungsten filament isn't an ideal black body, so its emissivity deviates slightly.

Glass envelope: The bulb's material can absorb some of the emitted light, especially UV radiation.


Overall, incandescent lamps are a practical approximation of black body radiation in the visible and near-IR regions.

What is the typical glass material in incandescent lamps?

The typical glass material used in incandescent lamps is soda-lime glass or borosilicate glass, depending on the application:

1. Soda-Lime Glass:

Commonly used for standard incandescent bulbs.

Composed primarily of silica (SiO₂), sodium oxide (Na₂O), and calcium oxide (CaO).

Suitable for general-purpose bulbs due to its affordability and ease of production.

Not highly resistant to heat or thermal shock but adequate for the temperatures of most incandescent lamps.



2. Borosilicate Glass:

Used in specialized bulbs (e.g., high-wattage or heat lamps).

Contains silica and boron oxide (B₂O₃), making it more resistant to heat and thermal shock.

Common in applications where higher durability and temperature resistance are required.




The choice of glass also depends on whether the bulb is designed to withstand specific conditions, such as higher operating temperatures, pressure, or exposure to chemicals.

[hamdani yusuf (OP)]

How much infrared radiation is transmitted through the glass?

The transmission of infrared (IR) radiation through the glass of an incandescent lamp depends on the type of glass used and the wavelength of the IR radiation. Here's a general breakdown:

1. Soda-Lime Glass:

IR Transmission: Poor for wavelengths beyond 2.5 ?m (mid to far-infrared).

Glass absorbs most of the longer-wavelength IR radiation emitted by the filament.

However, shorter wavelengths in the near-infrared range (0.8?2.5 ?m) can partially pass through soda-lime glass.


2. Borosilicate Glass:

IR Transmission: Slightly better than soda-lime glass for near-infrared radiation but still limited for mid- and far-IR wavelengths.

Its improved heat resistance allows it to handle high temperatures without significant structural degradation.


Efficiency:

A significant portion (up to 85?90%) of the energy from an incandescent lamp is emitted as IR radiation, but much of this is absorbed or reflected back by the glass.

To improve IR management, special coatings (e.g., dichroic reflectors) are sometimes applied to allow visible light through while reflecting or absorbing IR radiation.


If precise IR transmission values are needed, these depend on the exact glass composition and thickness, which can vary between manufacturers and specific lamp designs.

What's the ratio of absorbed and reflected infrared radiation by the glass?

The ratio of absorbed and reflected infrared (IR) radiation by the glass in an incandescent lamp depends on the type and thickness of the glass, as well as the IR wavelength. Here's a general overview:

1. Soda-Lime Glass:

Reflection: About 4?8% of IR radiation at each surface (depending on the angle of incidence and wavelength).

For typical soda-lime glass, near-IR wavelengths (0.8?2.5 ?m) reflect less than mid- and far-IR radiation.


Absorption: The majority of IR radiation (>80?90%) is absorbed for wavelengths above 2.5 ?m.

Soda-lime glass strongly absorbs longer wavelengths in the mid-IR and far-IR range, converting them into heat.



2. Borosilicate Glass:

Reflection: Similar to soda-lime glass, reflecting about 4?8% per surface.

Absorption: Less absorption in the near-IR range compared to soda-lime glass but still absorbs strongly in the mid- and far-IR range.

Slightly better transmission in the near-IR spectrum (0.8?2.5 ?m) than soda-lime glass.



Overall Ratio:

For incandescent bulbs with soda-lime glass:

About 85?95% of IR radiation is absorbed.

About 5?15% of IR radiation is reflected.
The exact distribution depends on the thickness and coatings on the glass.


For specialized applications, glass coatings (like low-emissivity or dichroic coatings) can be applied to alter this ratio, increasing reflectance to reduce heat loss or improving IR transmission for specific uses.

[hamdani yusuf (OP)]

When two systems in thermal contact are at the same temperature no heat transfers between them. When a temperature difference does exist heat flows spontaneously from the warmer system to the colder system until they are in thermal equilibrium. Such heat transfer occurs by conduction or by thermal radiation.[45][46][47][48][49][50][51][52]

The last sentence rises a question, what distinguishes thermal radiation from non-thermal radiation?

[alancalverd]

Nothing. Electromagnetic radiation is the same stuff, however it is generated.

[Bored chemist]

I spent several years working on "dynamic equilibrium" calorimeters for measuring ionising radiation dose rates. Long story but it was a cunning way of measuring millidegree temperature changes to better than 0.1% precision.

The classic Callendar and Barnes continuous flow water calorimeter uses a similar principle.

So... not Joule's method.
You found a method where the temperature difference between ingoing and outbound  was essentially constant.
OK.
I agree it's a very clever method.

It seems to be drifting rather from the point (so far as HY's threads ever have one)

[Bored chemist]

On teh other hand...

Note that objects heated by radiation from incandescent lamps can have higher temperature than the glass surface of the lamps. This pose question about thermal contact. Is exchange of kinetic energy through radiation counted as thermal contact?

It does not pose that question.

If you put a mirror round the bulb so that all the radiation was reflected back then the glass would  reach thermal equilibrium with the filament. (And it would melt)
But a bit like the Calender and Barnes continuous flow water calorimeter, the heat is continuously carried away from the glass (by the air round it, and by emission of IR) , so it never reaches the same temperature as the filament.
It never reaches equilibrium.


Paradoxically, even though quartz glass is nearly opaque to far IR radiation quartz halogen lamps were sometimes used as the "light" source for far IR spectroscopy.
The radiation used was actually that emitted from the quartz envelope.

[hamdani yusuf (OP)]

If you put a mirror round the bulb so that all the radiation was reflected back then the glass would  reach thermal equilibrium with the filament. (And it would melt)

You can put silver layer on the outside of the bulb glass, and additional insulation layers.

But a bit like the Calender and Barnes continuous flow water calorimeter, the heat is continuously carried away from the glass (by the air round it, and by emission of IR) , so it never reaches the same temperature as the filament.
It never reaches equilibrium.

It will melt before reaching equilibrium. But the surface of the glass bulb can be measured to have temperature between 150 and 250 degree Celsius.

[hamdani yusuf (OP)]

Paradoxically, even though quartz glass is nearly opaque to far IR radiation quartz halogen lamps were sometimes used as the "light" source for far IR spectroscopy.
The radiation used was actually that emitted from the quartz envelope.

According to Kirchhoff's law of thermal radiation, a good absorber is also a good emitter for the same radiation frequency.