Fresnel Lens

[HCl+NaHO=]

I was watching a Youtube DIY video regarding turning a broken flatscreen into a light.

What was intriguing was that there is a fresnel lens behind the screen. That for intents and purposes, “overcomes” the Inverse Square Law. And the light looks like sunlight with no falloff.

I was wonder if there is application of this type of lens, to not only diffuse LED lighting, but also to create a reef light without the typical ISL falloff.

In a nutshell, it seems possible to have the same PAR values at the bottome of the tank as at the top of the tank.

Just curious if anyone has done anything with this?

 

[oreo54]

Well there are many ways to "parallel" your light rays..
https://www.parabolixlight.com/fresnel-lens-and-parabolic-reflectors

Fresnel was designed to save weight and thickness not do anything that other lens types can't do..

Water itself, micro particulates ect will always make it so top to bottom par is not the same..and minor angle differences w/ photon paths.
Unless you use 100's of lasers..


Using narrow optics and hanging lights high is about just as good..

 

[HCl+NaHO=]

Well there are many ways to "parallel" your light rays..
https://www.parabolixlight.com/fresnel-lens-and-parabolic-reflectors

Fresnel was designed to save weight and thickness not do anything that other lens types can't do..

Water itself, micro particulates ect will always make it so top to bottom par is not the same..and minor angle differences w/ photon paths.
Unless you use 100's of lasers..


Using narrow optics and hanging lights high is about just as good..

This is pretty impressive

From this video.


(My think is that the lens is not like the lens in your diagram, say a standard fresnel. But one where the individual panes focus light to be diffuse)

I have also wondered in a blue filter, say over a diffuse panel of high intensity white light would have any benefits.

Anyway, appears to need more research.



Thirdly, I don’t think a reflector or narrow beam lens as you have exampled would be useful or effective on a panel of LEDs.

If the intention is to mitigate the flaws of LEDs. That is extreme shadowing, self shadowing, lack of diffusion, poor color blending.

Poor color blending would be negated as a problem if a white LED panel were to have a blue filter covering the entire panel. This is as per my idea that a blue filter would, indeed, work(which it may not).

Some of the best color blending(not in a matrix point source) with LEDs is to not have lenses at all. That is to say, using the native or default angle of 120•, do assist with blending. But this creates the problem of extreme light falloff, vis ISL.

 

[oreo54]

Filters seem to be only a negative proposition AFAICT.
What I mean is it doesn't add or spread color that isn't present in the orig beam.
A white diode (royal blue plus phosphors) will only subtract all but royal blue (theoretically, most aren't perfect).
Th Royal blue will still be a narrow band. Filter won't spread the wavelengths..

If one has photons to spare and doesn't want to change diodes then yea it "works"..

Actually "micro lens" diffusers are available that do use simple lenses. Only really small..

Abstract

Microlens array (MLA) diffusers for light-emitting diode (LED) backlight systems have been developed. A high fill-factor photoresist mold for the MLA was fabricated using three-dimensional diffuser lithography, and the patterns were transferred to a nickel master mold for UV-curable polymer replication. The fabricated microlens had various paraboloidal profiles, and its aspect ratio was controlled from 1.0 to 2.1. The MLA diffuser showed a batwing radiation pattern with a radiation angle of 150°. The fabricated MLA diffuser may greatly enhance the color-mixing characteristics of LED backlight systems and help reduce the number of LEDs required.
© 2006 Optical Society of America

So diffuse and collimate ..
Fresnels don't technicaly diffuse..

Funny thing is real native led angle is close to 180 (150-ish)..
That 120 is a lens..


Using TV panels for freshwater lighting has been kicked around before though I know of nobody who has done it.
As to reefing, usually the catch is strength..
It may seem bright to your eyes but it's usually not..
30 Lux coming of a TV is err "bright"..

NOTE: The Fresnel lens idea is a good idea..don't get me wrong.

Boils down to diffuse (mix) then collimate (focus)
Led blending hasn't been solved completely (actually some is a matter availability i.e using violet pumps in the 400-ish nm range and red/green/blue phosphors avoids the need for most blending issues, but I digress)

Good read...

Optical Diffusers

Fresnel Technologies' micro-lens arrays are well suited for optical diffuser use. We also offer diffusers for more unique optical applications.

www.fresneltech.com

 

[HCl+NaHO=]

Ya, I wrote 120 because Im not cutting it off. Unless it’s a burned UV “lens”. Which I have had to do.

I was just making an observation that the panel arranged LEDs without reflectors or external lens do simulate a T5 diffused quality. Provided they are mounted very close to the water. And have a pronounced fall off, because of that proximity.

I have the Vertex Illumina lights, they have point source shimmer and increased diffusion(T5ish), increased color blending. For example, there were others.

 

[Patrick Schools]

I currently have a Bicube 29 with power compacts. I purchased an Ai Prime HD. My plan is to gut it drill a hole in the hood and set the light on top of the hood. The problem is this will make the light too close to the water for a good beam spread. I plan to place a fresnel lens i recover from an old overhead projector inside of the existing light housing. I also have several diffuser elements from an old computer monitor. Fingers crossed.