Lens / reflector / optic for Ultra Bright 4 Watt RGBW NeoPixel

General project help for Adafruit customers

Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.
Locked
User avatar
scottmarchsmith
 
Posts: 4
Joined: Thu Dec 24, 2020 1:57 pm

Lens / reflector / optic for Ultra Bright 4 Watt RGBW NeoPixel

Post by scottmarchsmith »

Hi all -- working on a project with 16 addressable LED spotlights. I think the 4W RGBW NeoPixels (https://www.adafruit.com/product/5408) will do the trick, but I'm wondering about whether I need an additional lens / optic / reflector for each to make the light more focused as a spotlight. (New to this kind of LED work, I've worked mostly with strips before, never a DIY spotlight. Not even sure if what term is correct among lens / optic / reflector!)

Would a lens / optic / reflector be necessary to get a directional light / spotlight effect? If so, what are the critical specs for finding the right one? I am looking at ledsupply and ledil and am having trouble knowing what to look for.

Also, what would be a good strategy for mounting a lens / optic / reflector to the 4W RGBW NeoPixel board?

User avatar
adafruit_support_mike
 
Posts: 67454
Joined: Thu Feb 11, 2010 2:51 pm

Re: Lens / reflector / optic for Ultra Bright 4 Watt RGBW NeoPixel

Post by adafruit_support_mike »

To make a real spotlight, you'd need an elliptical reflector at the back and two spherical lenses in the front: one fixed and one moveable:

https://en.wikipedia.org/wiki/Spotlight ... optics.JPG
http://setlighting.tumblr.com/post/58531254165/the-leko

Mathematically, an ellipse has two focal points. Any line that begins at one focal point and reflects from the inner surface of the ellipse will go directly to the other focal point. The lines fan out past the focal point, but with a little tuning you can send them through a fixed 'collimating lens' that turn them into a cylinder.

If you then send that cylinder through another lens that can move closer to or farther away from the collimating lens, you can control the spread of the beam.

The fact that light from one focal point of an ellipse reconverges at the other focal point gives you the power to project a focused image of whatever is at the second focus. In a typical follow spot, you have a combination of an iris that controls the size of the beam and a pair of plates called the 'dowser' that can swing out to let the beam pass through, or swing together to block the beam completely.

In fixed ellipsoidal stage lights, the second focus has a slot that can hold pierced metal patterns called 'gobos', and is surrounded by four sliding metal plates called 'choppers' that can trim the circular beam to straight edges.

Computer controlled spotlights (called 'wiggle lights') add a pair of cylinders on either side of the second focal point called the 'scroller'. They hold a long strip of transparent plastic (the 'scroll') with different color filters printed every few inches, and can feed the scroll back and forth to change colors.

Fixed ellipsoidal stage lights have a set of clips at the end of the part that carries the moveable lens that can hold a metal frame that contains a color filter (called a 'gel'). Follow spots have a spring assembly called the 'boomerang' that can tilt any of (usually) six gel frames in and out of the beam path. Lifting a gel into position locks it in place, but the lock will release that frame when another gel is lifted into place.


The next step down from an ellipsoidal optical path is to put the light source at the focus of a parabolic reflector called a Parabolic Aluminized Reflector or 'PAR'. Lighting units that contain a PAR are called 'PAR cans'.

Mathemaically, any line that passes through the focus of a parabola and then reflects off the inner surface of the parabola will be parallel to every other line reflected from the parabola. You get the long-throw cylindrical beam, but not the ability to create focused images of things like an iris or gobos.

You can make a DIY PAR can from a literal #10 can and an old automobile headlight.


The next step down from a PAR can is to try and focus the light with just a spherical lens. Large spherical lenses are heavy and exensive though, so the simplest lighting fixtures will use Fresnel lenses like a lighthouse and are called 'Fresnels'.


I used to be a professional stagehand, duties including lighting tech and follow spot operator.

User avatar
adafruit_support_bill
 
Posts: 88093
Joined: Sat Feb 07, 2009 10:11 am

Re: Lens / reflector / optic for Ultra Bright 4 Watt RGBW NeoPixel

Post by adafruit_support_bill »

The spatial emission pattern of LEDs is different from halogen bulbs and not an ideal match for traditional parabolic reflectors. To more efficiently capture and focus the light, a TIR (Total Internal Reflectance) optic is typically used. These are generally molded from clear acrylic and either clip directly to the emitter or use some sort of mounting bracket. Many are optimized for use with a specific type of emitter. But there are more generic TIR optics out there as well.

Ledil and Carclo are two of the major suppliers of these.

User avatar
scottmarchsmith
 
Posts: 4
Joined: Thu Dec 24, 2020 1:57 pm

Re: Lens / reflector / optic for Ultra Bright 4 Watt RGBW NeoPixel

Post by scottmarchsmith »

Mike and Bill, thanks so much for your replies and sharing your expertise. I think, Mike, I'm learning that my use of the word "spotlight" might be pretty inaccurate to what a real spotlight is capable of. I'm after something less elaborate than a real spotlight, but I really appreciate understanding what it would take to put one together. I had not really considered focus at all, I was only thinking about limiting the spread of a superbright RGBW addressable LED to something like a circle. I guess maybe its more accurate to say I'm trying to use an addressable LED to produce a strong directional light..? Perhaps a digital wiggle light..? Still getting my terms in order.

The subject is basically a fixed diorama for a museum install, so, theoretically, the focus and spread won't need to change over and over interactively. But, it would be interesting to be able to test different calibrations of focus and spread to see the effects.

I'll look into TIR reflectors, and into collimating lenses. In the simplest version, I think the solution might be getting small cans to put the 4W PCBs into simply to limit the spread (?). Next step up: add a TIR reflector for the back of the can. Next step up: add a collimating lens. Next step up: add an objective lens.

User avatar
adafruit_support_mike
 
Posts: 67454
Joined: Thu Feb 11, 2010 2:51 pm

Re: Lens / reflector / optic for Ultra Bright 4 Watt RGBW NeoPixel

Post by adafruit_support_mike »

Bill is absolutely right that single LEDs are already more directional than light sources like an incandescent lamp.

A parabolic reflector will still work with an LED source, but there are a couple of modifications that will make things work better:

First, point the LED into the reflector rather than out toward the target you want to illuminate. That way all of the LED's light will bounce off the reflector and collimate (as long as the LED is at the parabola's focus).

Letting the LED point out toward the target will give you a cone of light that leaves the LED and passes the rim of the reflector without being collimated at all. That's especially a problem with LEDs, because most of the light they produce comes out in a cone.. their emission pattern is called 'Lambertian':

https://en.wikipedia.org/wiki/Lambert's_cosine_law

With an outward-facing LED source, you'd need a deep reflector to get any collimation worth noticing.

The Lambertian emission pattern will also cause trouble for a rear-facing LED though: the strongest light will go straight down the axis and reflect back along a path blocked by the LED itself.

The solution to that is the second modification: put the LED behind a lens with a really short focal length.. just shy of a hemisphere would be best. That will redirect almost all of the light to off-axis paths that won't be blocked by the LED on their way out of the reflector.

That approach gives you better performance and some flexibility: as long as you set the focal point of the lens at the focus of the parabola, you'll get good collimation.

That's slightly complex, but simpler than an ellipsoidal reflector system.

User avatar
chaperhead
 
Posts: 5
Joined: Mon Feb 03, 2014 12:19 pm

Re: Lens / reflector / optic for Ultra Bright 4 Watt RGBW NeoPixel

Post by chaperhead »

Hi I'm using 2541 addressable LED strip. Do the strips have a UL rating / E#. Trying to get 61010 certified.
Thanks Richard

Locked
Please be positive and constructive with your questions and comments.

Return to “General Project help”