輻照度與通量/輻射量有什麼區別?


6

我正在閱讀paper$^1$,它說注量能測量來自各個方向的入射輻射,並且注量類似於輻照度。它由$ \ phi(x)= \ int_ {4 \ pi} L(x,\ vec {\ omega'})d \ omega'$定義(刻度線似乎強調$ \ vec {\ omega'} $在集成過程中會有所不同,而不是固定的方向。)

從直覺上講,輻射是在一個方向上發出的光量,但其衰減量是與表面垂直的方向相距多遠。$ L = \ frac {d ^ 2 \ Phi} {d \ omega dA \ cos \ theta} $

輻照度是表面的面積光密度。$ E = \ frac {d \ Phi} {dA} = \ int_ {2 \ pi} L_i(\ vec {\ omega})\ cos \ theta d \ omega $

強度是從特定方向射向表面的光量。$ I(\ vec {\ omega})= \ frac {d \ Phi} {d \ omega} $

看起來您也可以將輻射度寫為輻射度乘以強度。$ L = E \ cdot I(\ vec {\ omega})$

看看公式,似乎輻照度將一個表麵點上的半球上的輻射總和並衰減了表面朝向光源的方向,而能量密度則將一個點周圍的整個球體上的輻射總和(以測量散射))。

維基百科說:"輻射通量是指表面每單位面積接收到的輻射能,或者等效地是隨著照射時間積分的表面的輻照度。但是這個定義似乎與上面給出的定義不匹配,因為它沒有時間。

https://www.researchgate.net/post/What_is_the_definition_and_difference_between_light_dose_and_light_fluence_rate

http://omlc.org/education/ece532/class1/irradiance.html

  1. 具有定向地下散射的半透明材料的實時渲染,亞歷山德羅·達·科爾索,2014年
3

I can only cite what I have learned in my lecture on Global Illumination techniques which was unfortunately some time ago:

  • Radiant Power : The amount of energy emitted by a light source in unit time. denoted by $\Phi$ and is measured in Watt which equals to Joules per second. (This does not specify any area!)

  • Irradiance: The irradiance denotes the incident radiant energy on a surface. It is defined as $E=\frac{d\Phi}{dA}$ - This quantity denotes the incoming energy per area and is measure ind $\frac{W}{m^2}$ Note here: radiant energy is measured in Watt which is Joules per second!

  • Radiant exitance: This is the reverse direction of Irradiance and is the energy an area emits in unit time and has the same definiton and units as Irradiance only with reverse direction $M = B = \frac{d\Phi}{dA}$. This is also often called radiosity B.

  • Radiance: Is the power per projected area per solid angle. It is defined as $L=\frac{d²\Phi}{d \omega * dA * cos\theta}=[\frac{W}{sr*m^2}]$ where $\omega$ denotes the solid angle, $\theta$ denotes the angle between emitting surface normal and the direction the energy is traveling to. So this is not attenuated by the distance but by the angles.

In general as I learned the distance between emitting and receiving surface is only important for Radiance because the projected area will be smaller if they are farther apart.

The time you are missing in your definitions seem to come from the conversion of Watt to Joules Per Second.