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  Topic Review (Newest First)
02-18-11 07:30 PM
RBTO
Re: If we want retroreflectivity as well??

Quote:
Harpmaker wrote: View Post

When we first started looking into making a DIY glass-beaded screen the cheapest (by far!) and most available beads were the ones used in the sign industry and for road marking paint. The problem is that compared to the "marbles" used in the HP screen those beads were literally "boulders". They are too heavy to be held in suspension in latex paint thin enough to spray and the image produced from beads that large also appears quite grainy.
Gotcha. I know the High Power screen beads are almost a "powder", being very small. That's clearly what you're looking for, I'm sure. It (the High Power screen) blasts a lot of light back at you really well!
02-18-11 02:33 PM
Harpmaker
Re: If we want retroreflectivity as well??

Thanks for the post and the scan Bob. What the High Power does it does well.

When we first started looking into making a DIY glass-beaded screen the cheapest (by far!) and most available beads were the ones used in the sign industry and for road marking paint. The problem is that compared to the "marbles" used in the HP screen those beads were literally "boulders". They are too heavy to be held in suspension in latex paint thin enough to spray and the image produced from beads that large also appears quite grainy.
02-18-11 11:05 AM
RBTO
Re: If we want retroreflectivity as well??

Quote:
Harpmaker wrote: View Post
The most known retroreflective commercial screen is the Da-Lite Highpower. They have recently changed the bead size on this screen. The older ones were said to use 9 micron beads; I'm not sure what the new screens are made with but the peak gain has dropped from 2.8 for the old to something like 2.4 for the new. You might want to try and get samples of these from Da-Lite for comparison.
Lurker here. I have a DaLite High Power screen and really like it. It holds detail really well and has the brightness I want, plus the angular falloff isn't so great that I can't live with it. I have a sample that I shot with the best "microscope" at hand (just a high res scan), which I'm attaching (sorry about the quality).

Saw this post and wondered if any of you have ever approached a road maintenance organization. They used to paint the road crossings where I worked and used glass beads that were fairly small. They would use the shake and bake (sun) method, and where the excess beads collected in the gutter, there was this bright shimmer until they washed away. I'm sure they have a somewhat cost effective supplier for this material. Just a thought.
09-18-10 02:33 PM
Harpmaker
Re: If we want retroreflectivity as well??

Quote:
KingLord wrote: View Post
Thanks again for the info Harpmaker, nothing like saving time since it's one thing we can't get back.
I hear that! And to think that some people so much time on their hands they try to kill it... the mind boggles.

Quote:
One quick question so I don't waste any more monets than I need to either - did you guys find if any beads were TOO refractive? I understand that the more refractive the less benefit you will get at off angles, but the benefit will be more intense. I know standard grades start at an index of around 1.5 and go up to 2.2+, and of course the expense climbs with them. In your tests do you know what you used and if there was a feeling they were about right, too little or too much in terms of intensity vs. viewing angle?
I seem to remember that the "perfect" refractive index of the beads should 2.0, which is twice the RI of air, for on-axis viewing brightness. Most of the beads we found were either around 1.52 or 1.94. I believe you are correct in thinking the higher RI beads would give a brighter image, but at the price of a smaller viewing cone. While I have read nothing to confirm this, I also think that higher RI beads would tend to exacerbate color-shifting in off-axis viewing. I would think that using beads with an RI between 1.5 and 1.6 would make the best all-around screen.

Quote:
In terms of the bubbles, those would come into play if the light hits one internally when it enters or leaves and would mess up the angle of reflection. With something of this size I'm not sure what the overall effect would really be, but it's safe to say bubbles are bad since they would cause more diffuse.
I agree.

Quote:
One quick note about the paint with the nanobeads, (those look to be about .1 micron?) I know the paint is super expensive but did it perform well or did it cause too much diffuse like you mentioned earlier with beads that are under 10 micron?

-KL
While we never found out the size of the beads in the U.K. paint I think they are no smaller than 5 micron and probably around 10 micron. That is why I said the larger beads in the photo were supposed to be 50 micron. My guess is that they are bigger. I think when the bead size starts dropping below 1 micron you will have diminishing returns on retroreflection until you actually get a diffusion effect. I read somewhere that NASA is using very small glass beads to get the flattest (most diffusive) paint possible, but I forget the context.

The U.K. paint (I forget it's name) did work quite well. They sell a white paint and a gray paint. Custy, our man in England, bought some and sent us some samples. The photos below, starting from the top-left and going clockwise are 1. thin layer of gray, 2. thin layer of white, 3. thick layer of gray, 4. thick layer of white - with a dime in the center for scale. First photo is with room light alone and shows no retroreflectiveness; the second photo is using the camera flash. You can see that the thick layers have lost their retroreflectiveness!

Room light



Camera Flash



The most known retroreflective commercial screen is the Da-Lite Highpower. They have recently changed the bead size on this screen. The older ones were said to use 9 micron beads; I'm not sure what the new screens are made with but the peak gain has dropped from 2.8 for the old to something like 2.4 for the new. You might want to try and get samples of these from Da-Lite for comparison.
09-18-10 12:54 PM
KingLord
Re: If we want retroreflectivity as well??

Quote:
Harpmaker wrote: View Post
It turns out that beads in this size range are used in some type of medical research and costs can be as high as several hundred dollars per gram! At that price it would cost many thousands of dollars to make even a small size DIY screen.

Another problem is that as the cost of the beads goes down the size RANGE goes up meaning there are a number of different diameter beads in the container. Any bead over 50 micron is too large, and even 50 micron might be as well. The photo below shows what I mean. You can see some of the beads are at least twice the size of others. If you look close (and it helps to know what you are seeing ) you can see air bubbles inside some of the beads; I'm not sure how much that would interfere with their retroreflectiveness. The beads in the photo are supposed to be 50 micron in size, which is about 3 times smaller than the beads used in reflective road signs and road paint! Now for the real kicker... look past the beads to the surface they are resting on, THAT is a coat of the U.K. paint I referred to in my last post, and those little bumps are THEIR glass beads!


200X



If you do any experimentation on a DIY retroreflective mix, please share your findings with us!
Thanks again for the info Harpmaker, nothing like saving time since it's one thing we can't get back.

One quick question so I don't waste any more monets than I need to either - did you guys find if any beads were TOO refractive? I understand that the more refractive the less benefit you will get at off angles, but the benefit will be more intense. I know standard grades start at an index of around 1.5 and go up to 2.2+, and of course the expense climbs with them. In your tests do you know what you used and if there was a feeling they were about right, too little or too much in terms of intensity vs. viewing angle?

In terms of the bubbles, those would come into play if the light hits one internally when it enters or leaves and would mess up the angle of reflection. With something of this size I'm not sure what the overall effect would really be, but it's safe to say bubbles are bad since they would cause more diffuse.

One quick note about the paint with the nanobeads, (those look to be about .1 micron?) I know the paint is super expensive but did it perform well or did it cause too much diffuse like you mentioned earlier with beads that are under 10 micron?

-KL
09-17-10 04:05 PM
Harpmaker
Re: If we want retroreflectivity as well??

It turns out that beads in this size range are used in some type of medical research and costs can be as high as several hundred dollars per gram! At that price it would cost many thousands of dollars to make even a small size DIY screen.

Another problem is that as the cost of the beads goes down the size RANGE goes up meaning there are a number of different diameter beads in the container. Any bead over 50 micron is too large, and even 50 micron might be as well. The photo below shows what I mean. You can see some of the beads are at least twice the size of others. If you look close (and it helps to know what you are seeing ) you can see air bubbles inside some of the beads; I'm not sure how much that would interfere with their retroreflectiveness. The beads in the photo are supposed to be 50 micron in size, which is about 3 times smaller than the beads used in reflective road signs and road paint! Now for the real kicker... look past the beads to the surface they are resting on, THAT is a coat of the U.K. paint I referred to in my last post, and those little bumps are THEIR glass beads!


200X



If you do any experimentation on a DIY retroreflective mix, please share your findings with us!
09-17-10 02:50 PM
KingLord
Re: If we want retroreflectivity as well??

Hi Harpmaker,

Thanks a lot for the reply and the info!

What you listed pretty much confirmed most of what I was already thinking.

Knowing what makes the "best" size helps me out heaps and gives me something to start with. Price I'm sure will be a sticking point, but I'll experiment with some samples and see if anything I can get is worth the effort and cost versus just buying a commercial screen.

I knew application would be a real beast on these, I've worked with metallics before and beads are a level up and then some beyond anything there.

Thanks for the warning on the hollow beads, I wouldn't have gotten them on purpose but would have probably jumped at a low price not knowing the real difference.

Anyway, I'll be sure to throw something up here if anything worthwhile ever comes out of my meanderings.

-KL
09-17-10 01:55 PM
Harpmaker
Re: If we want retroreflectivity as well??

Quote:
KingLord wrote: View Post
Hey guys,

Big lurker here, and I was looking to find a good DIY retro reflective solution when I stumbled onto this thread.

Wanted to ask if anyone had tried out the nanopowder beads like Anthony mentioned, and if they were too small to work? (I don't know a lot about optics.) If no one has tried it yet I might give it a go, I'm also curious about how a nano metallic would work as opposed to a silica.

Did you guys ever find a "normal" bead solution that made everyone happy?

-KL
Hi KL, welcome to the forum as an active participant!

From our group endeavors we have determined that the best size for glass beads to make a retroreflective front projection screen is between 10 and 20 micron. Much larger than that and the image may appear grainy, much smaller and the retroreflective property of the beads diminishes until they can actually become diffusive in nature.

The first problem we have yet to overcome is obtaining transparent glass beads in this size range at anything approaching an affordable price.

If a retroreflective screen paint was achieved, it would definitely be a spray-only solution; and even then it might be very hard to get even coverage so that "splotching" wasn't a problem (uneven dispersal of beads on the screen).

The beads used MUST be solid and transparent in nature. Ceramic beads are opaque and some glass beads are hollow - these simply won't work.

Much of our testing was done with a paint available from the U.K., but it is prohibitively expensive for making DIY screens.

As far as I know, there is no cost-affective DIY retroreflective screen mix available.
09-17-10 11:12 AM
KingLord
Re: If we want retroreflectivity as well??

Hey guys,

Big lurker here, and I was looking to find a good DIY retro reflective solution when I stumbled onto this thread.

Wanted to ask if anyone had tried out the nanopowder beads like Anthony mentioned, and if they were too small to work? (I don't know a lot about optics.) If no one has tried it yet I might give it a go, I'm also curious about how a nano metallic would work as opposed to a silica.

Did you guys ever find a "normal" bead solution that made everyone happy?

-KL
06-10-09 07:19 AM
custard
Re: If we want retroreflectivity as well??

it does look promising Mech.

got a few microscopic images of the material to show.

my microscope has an optical zoom of 20x, and any further magnification is carried out digitally using a sliding scale upto 200x. so i cant say how much zoom has occured between 20x and 200x in an accurate manner. the higher magnifications have some noise/abberation artifacts due to this aswell.

20x


about 50x


about 100x


about 150x


200x
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