# Tag Info

3

I know it's frustrating because it's nonintuitive, but it really is true. You can read about etendue at wikipedia or your friendly neighborhood optics textbook. I recommend Smith's "Modern Optical Engineering" . Or you can settle for the 2nd Law of Thermodynamics (aka "TINSTAAFL"), as GLR wrote in that what-if. It's a matter of surface brightness, and ...

3

I make f.lux, and I've chosen not to ship an overlay app for Android because I think it is a poor approach. It's hard to watch people say that these approaches are the "same" in any way, but I will try to bring numbers to the discussion, so maybe I will convince you. Measuring "melanopic response per lux" answers the question: at the same visual brightness ...

2

The human brain puts together a number of different cues to create depth perception. Some examples: The apparent (angular) size of the object. An object that is very far away is brought near a person's far point, but at the same time the magnification is very small, in such a way that the angular size of the object stays the same (so long as the eyeglasses ...

2

If the bulb is lit when you pour water on it, it will undergo thermal shock. Some parts cool down and shrink, while other parts are hot. This causes very large thermal stresses, which can break the bulb. Depending on the material and construction of the bulb, this may or may not result in a spectacular implosion (once the bulb cracks, the vacuum inside will ...

2

It is not quite this simple. The assumption you made is that the image of the fish eye lens is always on the focal point of the lens. This is only true for an object that is infinitely far away. In reality, the location of the image of the fish eye lens will depend on the distance the object is away from the fish eye lens. In practice, however, the object ...

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THere's a relationship between the mode radius (d), divergence (theta) and wavelength. For single-mode fiber, d x theta ~ wavelength. So, if you want a narrower diverging beam you'll have to deal with a larger mode diameter in the same proportion.

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The separation of spots in the diffraction pattern $y$ goes as: $y \sim \frac{\lambda L}{d}$ where $\lambda$ is the wavelength of light, $L$ is the distance from the slits to the screen the spots are shone on, and $d$ is the size of the slit. Clearly, the separation of the spots (and thus generally the precision that d can be measured with) increases with ...

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Gullstrand's equation says that the equivalent power of a thick lens ($P = 1/f$) is given in terms of its front and rear surface powers $P_1$ and $P_2$ by $$P = P_1 + P_2 - P_1 P_2 \frac{d}{n},$$ where $d$ is the separation between the surfaces and $n$ is the index of refraction of the lens material. For concave surfaces, $P_1$ and $P_2$ are negative, and ...

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Disclosure: I got to see your question because one of the replays refers to my article on blue light filters (glarminy.com). There is one important though, at first glance, subtle difference between approach 1 (f.lux) and 2 (Twilight). It is that approach 2 reduces contrast considerably more than approach 1. I'll get back to this point. First on blue ...

1

The property of light being collimated ("all going in one direction") is actually an interference property which requires the light to have a certain coherence in phase over its perpendicular extent. Light by its nature would rather spread out in all directions. To provide this pattern that perpendicular extent has to have a certain characteristic length ...

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