Focusing Flashlight Beam?

Cel · Sep 19, 2012

hoo7h said:
There is only one guy I trust that can solve this, he almost got an answer to everything, InfinitusEquitas

Lets see his judgment

By the time you see the light, it has moved away. Far away.

You can't slow down the light enough to see it moving with naked eye, but you can take a video with few billions of FPS and then watch it in slow motion.

BShanahan14rulz · Sep 19, 2012

The maxabeam is a short-arc HID, for whoever is wondering. Just as the name implies, it's like an HID, but with a much shorter arc that has higher radiance and can provide the small point source approximation needed for good collimation with reasonably compact optics.

The DEFT EDC uses not an XM-L, not even an XP-E, but an XP-C, partially because of its smaller apparent source.

InfinitusEquitas · Sep 19, 2012

hoo7h said:
There is only one guy I trust that can solve this, he almost got an answer to everything, InfinitusEquitas

Lets see his judgment

Cyp, and Cel are right... Not sure why there is an argument here to begin with...

godpower · Oct 22, 2012

Cel said:
Wrong, you hoo7h, are ignorant and annoying.

You won't see the light moving, cause it has to reach your eyes first! And it can't do that if it is still in the diamonds.

Even if you make a long line of them, you would still need a camera with a lot (few billions?) of frames per sec.

Wrong,light Travels at the same speed;Always.

If passing through glass,it will attempt to travel straight through,however it meets a molecule and gets reflected (Still the same speed), and reflects off another,and another. Eventually passing through the glass,this will cause the light to take longer to pass through.

But it never changes speed.

I know glass acts differently,but this is general. :yh:

Cel · Oct 22, 2012

godpower said:
Wrong,light Travels at the same speed;Always.

If passing through glass,it will attempt to travel straight through,however it meets a molecule and gets reflected (Still the same speed), and reflects off another,and another. Eventually passing through the glass,this will cause the light to take longer to pass through.

But it never changes speed.

I know glass acts differently,but this is general. :yh:

Wrong.

c is speed of light in VACUUM.

The speed at which light propagates through transparent materials, such as glass or air, is less than c. The ratio between c and the speed v at which light travels in a material is called the refractive index n of the material (n = c / v). For example, for visible light the refractive index of glass is typically around 1.5, meaning that light in glass travels at c / 1.5 ≈ 200,000 km/s; the refractive index of air for visible light is about 1.0003, so the speed of light in air is about 90 km/s slower than c.

Source: Wikipedia and other sources

Frankk · Oct 23, 2012

Light will slow down and diffract differently depending on the medium it's passing through.

Diffraction - Wikipedia, the free encyclopedia

godpower · Oct 24, 2012

Cel said:
Wrong.

c is speed of light in VACUUM.

The speed at which light propagates through transparent materials, such as glass or air, is less than c. The ratio between c and the speed v at which light travels in a material is called the refractive index n of the material (n = c / v). For example, for visible light the refractive index of glass is typically around 1.5, meaning that light in glass travels at c / 1.5 ≈ 200,000 km/s; the refractive index of air for visible light is about 1.0003, so the speed of light in air is about 90 km/s slower than c.

Source: Wikipedia and other sources

The short answer is No. Einstein's theory of special relativity is based on the idea that the speed of light is always constant. However, we CAN make it take longer for light to travel a set distance. In fact, we say that light travels more slowly in optically dense media. That statement is somewhat misleading.

As light travels through matter, though, it "bumps into" the atoms (technically, the photons keep getting absorbed and re-emitted), and so the light _appears_ to travel slower. We measure this phenomenon with a number called the index of refraction, usually represented by the variable 'n'. N is defined to be the speed of light in a vacuum divided by the slower speed in matter, and it depends both on the type of matter in question (different atoms/substances absorb and emit light in different ways) and the wavelength of light in question (different wavelengths of light get absorbed and emitted at different speeds, even in the same substance)

(I'm 16 and i knew this)

Cel · Oct 24, 2012

godpower said:
The short answer is No. Einstein's theory of special relativity is based on the idea that the speed of light is always constant. However, we CAN make it take longer for light to travel a set distance. In fact, we say that light travels more slowly in optically dense media. That statement is somewhat misleading.

As light travels through matter, though, it "bumps into" the atoms (technically, the photons keep getting absorbed and re-emitted), and so the light _appears_ to travel slower. We measure this phenomenon with a number called the index of refraction, usually represented by the variable 'n'. N is defined to be the speed of light in a vacuum divided by the slower speed in matter, and it depends both on the type of matter in question (different atoms/substances absorb and emit light in different ways) and the wavelength of light in question (different wavelengths of light get absorbed and emitted at different speeds, even in the same substance)

(I'm 16 and i knew this)

And you are wrong. That what 1 guy said doesn't mean that it will be true.

And that you are 16 doesn't mean anything...

Oh, and it depends about the material that you use. Nothing is perfect. And, why would light travel at the same speed, ALL the time?

Just my 2 cents.

Things · Oct 26, 2012

Why the hell are we arguing about the speed of light when it has no relation to the original guys question? The problem is the LED isn't a point source, as justinjja said.

Cyparagon · Oct 26, 2012

The speed of light is arguably always c. When we refer to the speed of light in practice, we actually mean the phase velocity. The propagation of the wavefront as it effects things. This "speed" changes depending on the environment.

Everybody is correct.

Cel · Oct 26, 2012

I agree, it is relative.

Anyway, it doesn't matter, cause we will never achieve that high speeds >200,000km/s.

Soren · Oct 28, 2012

This is the kind of misinformation that spreads when you get your physics education from minute physics.
Read this article: Refractive index - Wikipedia, the free encyclopedia
Watch this video at 18:40. Laser Fundamentals I | MIT Understanding Lasers and Fiberoptics - YouTube

die4laser · Oct 28, 2012

led is emitting light from a relatively large surface while laser is emitting from a "point" surface. So led cannot be focused a thin as a laser.

Cel · Oct 28, 2012

die4laser said:
led is emitting light from a relatively large surface while laser is emitting from a "point" surface. So led cannot be focused a thin as a laser.

Laser emits in narrow band of el.mag. spectrum, where LED emits in a wider band.
The size of the emitter does matter, but you can still focus LED to behave like a laser i.e. a narrow and collimated beam (but not as much as a laser), but you won't get a laser.

chipdouglas · Nov 1, 2012

hoo7h said:
There is only one guy I trust that can solve this, he almost got an answer to everything, InfinitusEquitas

Lets see his judgment

Sorry infnitus... I'm not bashing you, just trying to see this guys logic.

Hoo, what threads have you been reading to come to the conclusion that Infinitus is the most knowledgable person here when it comes to lasers/scienc?

michael.

InfinitusEquitas · Nov 2, 2012

chipdouglas said:
Sorry infnitus... I'm not bashing you, just trying to see this guys logic.

Hoo, what threads have you been reading to come to the conclusion that Infinitus is the most knowledgable person here when it comes to lasers/scienc?

michael.

No offense taken :crackup: When it comes to physics/science/lasers I claim no superior knowledge whatsoever.

I think that post was more of a backhanded comment on the fact that I had a tendency to post a lot, and at times be judgmental.

Focusing Flashlight Beam?

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