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Shining Light - The Physics Behind This Phenomenon?

by Sane
Tags: light, phenomenon, physics, shining
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Jan7-08, 08:07 PM
P: 223
I've taken a picture of my christmas lights. I'm wondering if someone could help me explain, or at least name, the phenomenon?

Why does light appear to come from 4 distinct points around the light? Even though some bulbs are rotated, the position of these 4 points do not rotate with it. It's always -up-, -right-, -left-, and -down-. Why?

If someone could link me to an article about this phenomenon, or at least give me a name of it, that would help a lot. Some of my friends are saying it has to do with spherical aberration. But I don't understand how. It seems, to me, to be spherical aberration and the following pattern at the same time:

Which could be caused by refraction, right? But how?

Thanks for any replies.
- Sane
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Jan7-08, 08:11 PM
P: 117
what happens when you rotate the camera?

It could be diffraction or saturation of the detector array.
Jan7-08, 08:21 PM
P: 223
It's always up with respect to the orientation of the camera. I took another picture to clarify:

So I guess that means it has to do with the lens inside the camera. Is there anything specific I can research?

Jan7-08, 09:17 PM
P: 22,313
Shining Light - The Physics Behind This Phenomenon?

It's diffraction spikes - we actually had a thread about this recently:
Jan7-08, 09:27 PM
P: 223
Diffraction spikes, brilliant! Thanks. I get many excellent hits with this term.

Loren Booda
Jan7-08, 09:47 PM
Loren Booda's Avatar
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Do eyelashes cause a similar phenomenon? How about the iris of a camera?
Jan7-08, 10:21 PM
P: 223
Quote Quote by Loren Booda View Post
Do eyelashes cause a similar phenomenon? How about the iris of a camera?
It seems like it'll be anything that obstructs light directly before entering the lens. You can even place strings in front of a telescope and get diffraction spikes (as russ_watters has apparently done).
Jan7-08, 11:47 PM
P: 223
I could not find an objective explanation of Diffraction Spikes anywhere... not even on Wikipedia. Most sites just referenced little things you could do, and the overall effect. I found a couple sites that explained very briefly what happens, so I tried to piece together all of these things to make the following analysis of my photo.

(Disclaimer: This may not be 100% accurate, but if it helps anyone else who stumbles upon this thread get a better understanding of Diffraction Spikes, then great. And maybe someone could help correct any inaccuracies/elaborate on my analysis.)

When you observe this photo, you will see that there is light radiating horizontally and vertically from each light bulb. The light does not radiate in a sphere, but rather in four directions. Also, even though some of the light bulbs are rotated, the lines of light do not rotate with it. Why does this effect occur?

This optical phenomenon is known as “Diffraction Spikes”, and is common in many astronomy photos. The effect is apparent whenever a bright source of light is viewed through a lens with support vanes that obstruct light. This lens can potentially be the lens of a camera, glasses, or even your eyes.

When a lens is directly obstructed with anything thin and solid, light waves will bend around and constructively interfere on the other side, creating thin lines of light in the shape of the obstructive item. This effect becomes more noticeable as the amount of light entering the lens increases. In this case, the diffraction spikes do occur in all of the image’s light, but is only visible for the brightest sources.

In the camera, due to the way the lens was constructed, the lens has support vanes in the pattern of a crosshair. As a result, the interfering light is a horizontal and vertical line.

The item that obstructs the light may be anything thin and solid, even an eyelash. That is why if you squint and look at a bright light, you can get the same effect, due to your eyelashes behaving like support vanes in a camera’s lens.
Jan8-08, 12:11 AM
P: 93
i don't understand how a solid object can bend light... i thought you need strong gravity to do that, as in huge stars in space? Shouldn't you just get a shadow star or something...
Jan8-08, 12:37 AM
P: 223
That's one thing I wasn't clear on myself, and need to explain better once I understand it more. I don't think it's so much that it's bending it, but that the waves can go around obstacles. And that results in interference. Similar to the Double Slit Experiment. I think... Clarification, anyone?

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