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2
votes
1answer
24 views

Why is radiance measured normal to the beam?

Radiance is defined as: $L=\frac{d \Phi}{\mathop{d \omega} \mathop{d A} \mathop{\cos\theta}}.$ I’m wondering why there is a $\cos \theta$ factor in the denominator of the radiance ($\theta$ is the ...
0
votes
0answers
36 views

Reflectivity of gases

According to the principle of the conservation of energy, the following is true for an object: emissivity+reflectivity+transmittance=1; where emissivity=absorbtivity according to Kirchoff. When ...
4
votes
5answers
531 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 ...
0
votes
0answers
25 views

Radiometric Intensity of Non-Monochromatic LED

So I have a problem with the LED with the spectrum shown below I am asked to find the radiometric intensity in Watts/steradian given that the LED produces $5.6\times 10^{-3}$ mcd. We are also told ...
3
votes
2answers
207 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 ...
1
vote
2answers
105 views

Irradiance at surface point due to lighting from point light source

I'm reading through a computer graphics paper and author says that the radiant intensity emitted by an infinitely small surface point $p$ with normal $ n $ into direction $ \omega $ is $$ I_p(\omega) ...
1
vote
1answer
336 views

Lambert's cosine law

I am learning how to physically render images in computer graphics. I just saw that the area that gets light is given by the Lambert's cosine law. In my head it makes perfect sense the relation but ...
1
vote
0answers
27 views

Hemisphere irradiance

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 ...
4
votes
1answer
568 views

Relationship between irradiance and radiance

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 ...
3
votes
2answers
1k views

Relation between Radiance and Irradiance

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 ...
1
vote
0answers
92 views

How efficient is the Crookes radiometer?

I remember many years ago, I think at 8th grade, seeing the teacher show us a Crookes radiometer. I remember it being very fascinating. Today I read the wiki article on it, after looking up what it ...
3
votes
1answer
505 views

Radiance equation

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 ...
1
vote
1answer
223 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 ...
0
votes
1answer
290 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 ...
0
votes
1answer
178 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 ...
-2
votes
2answers
1k views

How reliable is Radiometric dating? Are there limitations? [closed]

Young earth creationists dismiss radiometric dating as unreliable, whats the truth?
4
votes
2answers
263 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 ...