Home / Halogen Point Heater / Basic knowledge of Halogen heater / 5.Physics of light heating / 5-3.About the wavelength of the radiation temperature

If there is near-infrared mainly from the heater, or far infrared rays mainly from the heater, which is determined by the temperature of the heating element rather than the material.

Peak wavelength of the electromagnetic wave λm
Temperature of the heating element T ℃

Peak wavelengthλm=2896/ (T+273)μm (Wien’s displacement law)

It will be shown below when determining the peak of the emission wavelength at each temperature than the above equation.
It will also widely distributed to the long wavelength side to the short wavelength side as the peak emission wavelength.
Short wavelength side is up to about one-third of the peak wavelength, but about five times until you come out the long wavelength side.
It is distributed in a wide range more in fact, as it can see from the formula of Planck’s course, but the number is so extremely small, there is no little sense.
The valid range is 0.5 to 3 times the peak wavelength.  Absolute temperature unit shown above [K].
It becomes Celsius [℃] Subtracting 273 from now.
Graph of 300 [K] is 27 ℃ ambient temperature, radiation from the human body (body temperature) is close to this.
Graph of 3000 [K] is equivalent to the radiation of a halogen lamp.

It becomes one-tenth scale drops one position than the peak radiation intensity because it is a logarithmic scale, it will be the 100th in the scale under 2.
Therefore radiation range of substantially means is in the range of up to 1 scale under approximately from the peak.

Does not mean there is no emission of long wavelength from the heating element of the high-temperature As can be seen from the figure above.
Radiation of a wavelength longer will be more about high temperature rather. But the proportion is only little.

It is unlikely that the radiation intensity is greater than the value shown above the graph.
Emissivity is called 　 “The black body” the substance of 100% in the wavelength range of all, and that is the value shown above.
Substance of reality because it is less than 100% is always emissivity, will be lower at all wavelengths than the figure above graph.
The wavelength dependence of emissivity is not a constant matter of reality, there is not also mean that similar shape at all in the form of a mountain in the figure above graph, but it becomes the form of the figure above graph almost Basically, such as the composition of the object by difference is insignificant.

“Radiate intensity and wavelength distribution” of the figure above, you will be prompted by the “Planck’s law” and as will be discussed below, the practical use and may even simply by utilizing the graphing calculator so quite troublesome.

W(T λ,) radiation energy density of the unit area and per unit wavelength in black body

W(λ,T) = 8πhc/λ5/( exp( hc/λkT ) -1)　[w/m2]

λ:wavelength　　[m]
T:black-body temperature　[K]
c:speed of light 3 × 108 [m / s]
k:Boltzmann’s constant 1.3807 × 10-23 [J / K]
h:Planck’s constant 6.626 × 10-34 [J ・ s]

In summary above the formula using the C1, C2

C1( 1st radiation constant )=2πhc2=3.7427×10-16　[W・m2]
C2( 2nd radiation constant )=hc/k=0.014388　[m・k]

W(λ,T) =C1/λ5 /(exp(C2/λ/T)-1) [w/m2]

Energy of one photon pe = hν = hc / λ
Average number of photons – 1 / (1 (hc / λkT) exp)

The figure below is a reference that is easy to see a little more detail of “Radiate intensity and wavelength distribution”.
Unlike documents earlier, the unit of radiation intensity so has become radiation per unit solid angle to the [w / cm ^ 2 / sr / μm], you need to × 2π to fix the total radiation from the plane.

Visible light is in the range of about 0.4 – 0.8μm.
There is called ultraviolet about 0.4μm or less.
There is called infrared 0.8μm or more.
It is classified as near-infrared far infrared rays, it follows about 4μm above, but does not mean much less in this category.
Mechanism by which light is converted into heat is the same.
There is no work of except that changes to the infrared heat.  ※ Red line (calculated expected value) graph radiation characteristics of the halogen lamp is black body radiation of 2600K.

Temperature 1 is halogen lamp of 3200K of (life 200 hours).
Temperature 2 is halogen lamp of 2900K (2000 hours life).
Temperature 3 is halogen lamp of 2600K (more than 5000 hours life).

These are that reflects the transmission characteristics of the quartz glass bulb and emissivity properties of tungsten to black body radiation.
It will be less than one third the total radiation than the black body radiation of the same temperature by emissivity properties of tungsten (light emitting material) mainly.
Also due to the characteristics of the quartz glass does not devitrified and characteristics of the tungsten emissivity is lowered as long wavelength, a wavelength of about 4μm above, the wavelength of 4μm s is nearly zero. The following figure shows the spectral transmission characteristics of optical materials ,silicon and germanium.
Transmittance is approximately 93% in quartz glass, but this is because about 7% reflection.
There is almost no absorption in the visible light region quartz glass.
Since there is a reflection worth about 7% other materials, must be considered by subtracting the absorption rate it.
Pure quartz has been used as a communication optical fiber.
This is a transparent body near perfect as tens of km also send a light signal.    