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-   -   Fresnel lens properties (http://physicshelpforum.com/light-optics/15127-fresnel-lens-properties.html)

Camerart Mar 3rd 2019 05:39 AM

Fresnel lens properties
 
Hi,

Can anyone tell me the transmission properties of a plastic fresnel lens, that I got from a microfiche viewer?

I'm particularly interested in: Will it pass UV light?

If so, when focused to half, will it be double strength, so double heat, light and UV?

Camerart.

oz93666 Mar 4th 2019 02:06 AM

First .... what is the lens made of ??? glass or acrylic ...

My guess is glass , different glasses have different transmition properties

Suppose you have a 10 cm x 10 cm lens and you focus the sun to a 1 cm x 1 cm size ... the area has been reduces by 100 times so you will get 100 times the light intensity ...minus loses from scattering from the lens , and absorption by the lens... perhaps 15%

Camerart Mar 4th 2019 06:00 AM

Hi O,

The lens is made of Plastic.

C

oz93666 Mar 4th 2019 06:17 PM

Quote:

Originally Posted by Camerart (Post 42713)
Hi O,

The lens is made of Plastic.

C

That would most likely be acrylic , also called perspex ...

Put "transmission wavelengths of acrylic " in google search and you get charts like this ....

https://www.thorlabs.com/images/TabI...ission_2mm.gif

A search also shows ..."Unlike glass, pure acrylic (PMMA) does not filter ultraviolet (UV) light. Acrylic can transmit UV light down to 300 nm. Standard acrylic, like e.g. Plexiglas, includes an additive to make the acrylic absorb UV light"

https://www.researchgate.net/profile...-radiation.png

Camerart Mar 5th 2019 03:01 AM

Hi O,

Excellent, thanks for your research.

Just to let you know why I ask. I have a tortoise that needs the warm seasons extending, which I do now by keeping her indoors, with a 150W reflector lamp heating her, till she's over 30Deg. I wanted to make a frame with the fesnel lens, outside, where she can get double-ish the light, heat and UV, from the low sun at the moment. (I'll be careful about bright days)

Cheers, C.

oz93666 Mar 5th 2019 09:07 PM

Quote:

Originally Posted by Camerart (Post 42725)
Hi O,

Excellent, thanks for your research.

Just to let you know why I ask. I have a tortoise that needs the warm seasons extending, which I do now by keeping her indoors, with a 150W reflector lamp heating her, till she's over 30Deg. I wanted to make a frame with the fesnel lens, outside, where she can get double-ish the light, heat and UV, from the low sun at the moment. (I'll be careful about bright days)
Cheers, C.

Ahh I see .... I would suggest a lens will not help .... A lens focuses heat into one small area , it does not increase the amount of energy entering the system .. It will get no hotter with a lens than with a glass roof , and anyway it's probably at night that the temperature drops...

If I were doing this I would just make a very well insulated den for the creature , expanded polystyrene , straw , or similar then his own body heat will not escape , and there's no danger of over cooking , as in sunlight ...

He has evolved to live outside , so just a little help is all that should be needed.


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