# Tagged Questions

The tag has no usage guidance.

288 views

### Visibility of moon-based laser from Earth

If someone (or some robot) on the moon were to point a laser at the Earth, how many watts would the laser need, to be easily seen with the un-aided eye from Earth? Obviously this depends on a number ...
7k views

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 ...
602 views

### Is there no radioactive decay between nuclear fusion and solid material formation?

I'm aware my question might be considered a duplicate of this one: Radio-dating and the age of the earth I read that one and I looked everywhere and I still can't find my piece of mind. I would ...
1k views

A question related to radiometry: Irradiance $E$ at a point $x$ can be written as: $E = \int_\Omega L(x, \omega) cos(\theta) d\omega$ I understand this formula and where it comes from. The equation ...
951 views

I am trying to understand the equation of the radiance, but there is one thing i don't understand: $L_r = \frac{d^2\Phi}{d\omega \space dA\cos{\theta}}$ Why is that second exponent there in the ...
1k views

### Why does lambertian surface reflection result in uniform radiance measured from every direction?

I'm reading through the light measurement handbook and page 28 is confusing me. I knew previously that lambertian diffuse reflections distribute the reflection of incoming intensity such that the ...
54 views

516 views

### 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 ...
24 views

### Geometric and radiometric distribution of light

I'm studying the behavior of the light in a scene, to know how much light arrives at a specific point of a surface and how much of it leaves from the point. From the documentation I'm reading, it says ...
54 views

How do I calculate sky irradiance from radiance (L) from a hemisphere above a surface which is tilted relative to the normal (x=0,y=0,z=1). I have L as a function of zenith (0 to 180deg) and azimuth (...
203 views

### Leaching of radiometric material, is it possible?

I've been doing some reading about radiometric dating and I've come across an interesting find. If anybody has any additional information on this, that would be great. First my question: In regards ...
73 views

### Is shape of a black body much of a concern in physics?

When I read a book on computer vision, I stumble upon the ideal black body model. Using Lambert's cosine law (wiki), one is able to compute the intensity of an area element dA w.r.t. some observer. ...
343 views

### Implementing a black-body using Planck's Law in a 3D ray tracer

1_ In one of my software projects, I need to implement Planck's Law in terms of wavelength. I can't be sure if it's right because I've seen different variations of it, and all the implementations ...
23 views

### 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 ...
7 views

### 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 ...
38 views

### Remote sensing reflectance

I am not getting something simple for reflectance for a lambertian surface when dealing with remote sensing applications. I am trying to derive the equation from http://landsathandbook.gsfc.nasa.gov/...
64 views

### Why do some materials follow Lambert's cosine law?

I perfectly understand Lambert's cosine law, so I can apply it, it isn't really that hard (now that I got it :) $$I_n=I_\theta*\cos\theta$$ What I don't understand is why some materials follow this ...
379 views

### How does a radiometric infrared camera estimate an objects temperature?

Say we have an infrared camera which measures some amount of radiation, in a spectral bandwidth which is given, between wavelength $\lambda_1$ and $\lambda_2$ from a perfect black body. How is it ...