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13 views

What is difference between Irradiation & Radiosity?

I have a question in Radiometry: What is difference between "Irradiation" & "Radiosity" in Radiometry? Assumption: the emission & the reflection are specular. I know these physical ...
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1answer
106 views

How do I convert lux to lumens

Overview... I'm a novice in the very basics of light physics and calculation between various units. I'm sure this is a very simple problem to those who know the process. And, before we continue, this ...
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38 views

Energy dependence of integrating dosimeters

The graph shows the relative response of a dosimeter at different energies, normalized to 1.25 MeV Co-60 gamma rays. Curve A is the graph of the equation $$ ...
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1answer
62 views

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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2answers
56 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. ...
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41 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 ...
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0answers
35 views

What exactly is $\theta$ in Radiance formula?

The definition of radiance is: $$L\equiv\frac {\partial^2 \Phi}{\partial \omega\,\partial A\,\cos\theta}$$ where: $\Phi$ is the radiant flux $\omega$ is the solid angle $A\cos\theta$ is the ...
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2answers
69 views

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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2answers
138 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 ...
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1answer
157 views

Polonium tea emergency [closed]

Let's assume that I just realised that tea I drunk 30 minutes ago during meeting with a secret agent was doped with radioactive polonium. What should I do? What the doctors will do? Are there ...
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1answer
53 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 ...
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0answers
47 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 ...
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5answers
579 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 ...
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3answers
481 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 ...
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2answers
192 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) ...
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1answer
440 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 ...
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0answers
39 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 ...
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1answer
800 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 ...
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2answers
3k 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 ...
3
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1answer
719 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 ...
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1answer
369 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 ...
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1answer
314 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 ...
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1answer
191 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 ...
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2answers
2k views

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

Young earth creationists dismiss radiometric dating as unreliable, whats the truth?
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2answers
276 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 ...