# Tagged Questions

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### What's the meaning of partial derivative for radiance?

The definition of radiance is: $$L\equiv\frac {\partial^2 \Phi}{\partial A\,\partial\omega\,\cos\theta}$$ where: $\Phi$ is the radiant flux $\omega$ is the solid angle $A\cos\theta$ is the ...
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### Irradiance from a light bulb hitting spheres

I'm reading a book saying that irradiance is W/m^2. It continues: For the point light source example in Figure 5.6, irradiance at a point on the outer sphere is less than the irradiance at a ...
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### Why does radiance remain constant along rays of light through empty space?

In Radiometry, radiance (L) is defined as flux density per unit area per unit solid angle. If we move further along a ray, away from a point, shouldn't the radiance decrease? I am unable to grasp an ...
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### How can I measure radiance?

I'd like to measure radiance in order to see how accurate the Lambertian, Phong models are and maybe to measure the "shininess constant" of a material (which appears in the Phong Model) on some ...
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I know the radiance is expressed as $$\text{[Radiance]} = \frac{W \cdot m^2}{\text{sterad}}$$ and $$\text{[Irradiance]} = W \cdot m^2$$ But what's the relation between theese two quantities? Is the ...
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### Find the spectral distribution of a metallic reflection given electron configuration

If I have the electron configuration for a metallic element, how do I find the spectral distribution of its specular reflection? For example, for gold (2,8,18,32,18,1) I should get a greater ...
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### Photosensitivity of Photodiodes, lower wavelength -> lower sensitivity?

I saw a diagram of the photosensitivity (Current per Power) of a photodiode. So there is this diagonal stating the 100% quantum efficiency. I wondered why the sensitivity for bluer light lower ...
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### How reliable is Radiometric dating? Are there limitations? [closed]

Young earth creationists dismiss radiometric dating as unreliable, whats the truth?