Shape of torchlight?

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Airspeed
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Shape of torchlight?

Post by Airspeed »

I have a torch, fitted with a rectangle array of LEDs.
At a range of 50mm, it sheds a rectangular light shape. :)
At a range of 500mm+, it illuminates a disc, like any single globe torch. :dunno:
Can any of our boffins here explain the change in shape?
If needed, I can scan the torch and show a video of the light shape.

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Tako_Kichi
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Re: Shape of torchlight?

Post by Tako_Kichi »

I have one of these......

https://www.amazon.ca/Taclight-High-Pow ... oogcana-20

At x1-x25 zoom levels the light shape is square but the edges get softer the more you zoom out, at zoom ranges above x25 the light shape is circular like a regular flashlight. The 'feature' is a function of the lens/reflector design and is similar to the way a zoom-able camera lens will produce 'vignetting' at certain zoom levels but not others.

Your flashlight may not be zoom-able but at different focal lengths it will produce different image shapes as you have discovered.
Larry

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Tomliner
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Re: Shape of torchlight?

Post by Tomliner »

If I remember my physics lessons correctly the spread or intensity of a beam of light is proportional to the square of the distance travelled so I would imagine that if the rectangle or square shaped pattern at short range is less than perfect then as distance increases those imperfections would become greater. May be there is some clever optical design in the lens involved as well.
Then again maybe I’m talking a load of cobblers! EricT *-)
Now at the age where I know I like girls but can't remember why!

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Tako_Kichi
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Re: Shape of torchlight?

Post by Tako_Kichi »

In the case of my flashlight the glass is very definitely a strong lens and is almost like half a marble or the eyeball of a cat the curvature is so pronounced. As you slide the head of the flashlight back and forth you change the distance (or focal length) between the light source and the lens which in turn varies the size, shape and intensity of the projected beam. As the projected image becomes larger the brightness is reduced but the lens compensates for that much better than a flat piece of glass would do.

In Mike's case he has a fixed distance between the light source and front lens (which may even be just flat glass) and so he will only see the change between a rectangular image and a round image when the distance between the flashlight and the target surface is changed whereas I see the difference at any distance depending on how far my lamp/zens combination is zoomed in or out.
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Re: Shape of torchlight?

Post by Airspeed »

This shows what I mean:
Image

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