The Effects of Reflector Design and Lamp Orientation

[Me2!]

Interesting. So tarnishing is endothermic. Thats handy.

Any idea what coating is on the dichroic reflectors?

[SmC252]

Originally posted by Me2!
Before someone responds with the " but mirrors are made with silver so how could chrome plating be more mirror like?" question, look at your plated items.

The silver in a mirror is protected by glass and some black finish. Silver tarnishes. The rate of a chemical reaction is logarithmic. every 10degrees C doubles the reaction rate. This will be close to a very hot lamp. How often do you want to polish it?

I have a chrome racing bike that I got custom plated 20years ago and its still shiny like a mirror. Shiny car parts are chrome for the same reason - they stay shiny.

Hey everyone, this is my first post here but I felt I needed to comment. My backround is mostly in performance automotive, I've worked as a mechanic at several speed shops, no fast-n-furious crap for me. We use to do fabrication, mainly 304 stainless steel, also mild steel and aluminum. I also have experience with coating metals, powder-coating, anodizing and lots of general mechanic skills and a huge DIYer. I have studied for several years in 2 different automotive schools to learn all I could, with numerous certificates. I'm 21 years old and live outside of Boulder, CO.

Basically, my experience with chrome is that it has a fairly low heat tolerence. It turns blues and purples and even flakes off with enough heat. (Yeah, it's not good on the white-hot race manifolds.) Quite honestly I am suprised I have yet to read anyone mentioning the color WHITE when painting for reflection. Power-coating the surface white would work great, as it is VERY reflective and will not stress from heat. I may try this. The second option would be to POLISH that aluminum or Stainless part, you'd be surprised how bright aluminum especially can get. I will for sure try this before trying a white finish.

Also, isn't solder like 95% silver? Why not just get the really thick torch-solder and melt that inside the reflector? Probably would take a while but that's basically all that silver plating guy will end up doing.

-Steve

[Me2!]

Good to know chome doesnt like heat.

I thought platers dip into a tank and pass a current through? Just melt solder on? Is this really a method they use?

The layer has to stay even for our purpose so as not to distort the optics. I can see this happening in a dipping tank but not with a stick and torch.

[Dazzzla]

I thought platers dip into a tank and pass a current through?

correct

Just melt solder on? Is this really a method they use?

incorrect

DJ

[Guy Grotke]

White painted surfaces can be very reflective, but they make very bad mirrors! The difference is a diffuse reflection versus a specular reflection. White objects give you a diffuse reflection with the light rays going in all directions. A uniform metal surface can give you a specular reflection with each ray following the angle of incidence = angle of reflection relationship. This is why we don't use pieces of white paper as mirrors.

To direct all the rays to where they need to go, we need a specular reflection. There are lots of ways to get a uniform metal surface: Classic mirrors are silver chemically deposited on a smooth glass surface. Plating uses electrical current to coat a conductive surface with metal atoms by neutralizing the charge on metallic ions in a solution. Vapor deposition lets you precisely control the thickness of a metallic coating on an object. Polishing mechanically removes everything but the uniform surface.

Most reflectors are made by a combination of such processes. Plating is not at all the same as dipping in solder, but I think you could make a rough silver coating if you started with a very clean copper reflector and then dipped it in molten silver. This would be a bit tricky, since silver melts at 961 C, and copper melts at 1083 C. So you would need very good temperature control. After coating, you would need to polish the surface to make it specular. This would all be much more difficult and expensive than electroplating.

Soldering the copper surface with a modern lead-free solder would not work at all, since such "silver solders" are mostly tin. (They just don't have any lead.)

[ace3000_1]

and copper melts at 1083

940 - 1083.6 deg c.

Polishing mechanically removes everything but the uniform surface.

I disagree with that. Take a look at a microscope level and you will see

Trev

[SmC252]

Originally posted by Dazzzla
correct

incorrect

DJ

I didn't mean to cause any confusion. I am simply saying you COULD use solder to coat a piece of metal and use it as a reflector.
Plating is a simple process and this is how you do it; You take a container, put hydrochloric acid in it, connect the electricity to the item to be plated and also to the acid to complete the circuit. You put the clean metal in and let the plating happen untill the desired thickness is reached. I'm pretty sure Chrome is 1 coating of tin then 2 or 3 coatings of nickel to give that nice luster. This is very similar to anodizing aluminum (same acid works but you use a special dye) and I know of people who have done a DIY job and it turned out as good as a pro job, provided enough power. As for powdercoating, this may be a bit more feasable as you can buy the whole setup for under $200 and will use it on other things too.

Originally posted by Guy Grotke
White painted surfaces can be very reflective, but they make very bad mirrors! The difference is a diffuse reflection versus a specular reflection. White objects give you a diffuse reflection with the light rays going in all directions. A uniform metal surface can give you a specular reflection with each ray following the angle of incidence = angle of reflection relationship. This is why we don't use pieces of white paper as mirrors.

To direct all the rays to where they need to go, we need a specular reflection. There are lots of ways to get a uniform metal surface: Classic mirrors are silver chemically deposited on a smooth glass surface. Plating uses electrical current to coat a conductive surface with metal atoms by neutralizing the charge on metallic ions in a solution. Vapor deposition lets you precisely control the thickness of a metallic coating on an object. Polishing mechanically removes everything but the uniform surface.

Most reflectors are made by a combination of such processes. Plating is not at all the same as dipping in solder, but I think you could make a rough silver coating if you started with a very clean copper reflector and then dipped it in molten silver. This would be a bit tricky, since silver melts at 961 C, and copper melts at 1083 C. So you would need very good temperature control. After coating, you would need to polish the surface to make it specular. This would all be much more difficult and expensive than electroplating.

Soldering the copper surface with a modern lead-free solder would not work at all, since such "silver solders" are mostly tin. (They just don't have any lead.)

I've soldered copper surfaces before and it's not a problem at all, but I do agree it isn't the BEST way to do this. And like I said, I have commonly found real 97% silver solder locally. If someone wanted to do this, then a torch and some thick solder/flux from the hardware store is all you'd need. I don't understand why you think a mirror is so much better then a proper white powder-coating or even a polish job. If the right white color is obtained I guarantee it will be as good, if not BETTER then a mirror unless it's a $200 mirror. Maybe you will get 10% more light but when working with a 400watt system, is that extra 40 watts going to help? Most won't even pass the LCD, but it is important to get it there. I have personally polished stainless and aluminum to a mirror finish and it only takes 6 hours or so for a reflector-sized piece. Aluminum is softer and sands much easier.

-Steve

[Dazzzla]

I don't understand why you think a mirror is so much better then a proper white powder-coating or even a polish job. If the right white color is obtained I guarantee it will be as good, if not BETTER then a mirror unless it's a $200 mirror. Maybe you will get 10% more light but when working with a 400watt system, is that extra 40 watts going to help? Most won't even pass the LCD, but it is important to get it there.

I suggest that you do some more research

DJ

[charlie10]

I talked to a local silver plating shop, they implied plating the Ikea Soare reflector would be about us$30-50. It would need nickel plating first (not sure if that's another $30-50). Curious if it's that expensive elsewhere? Also curious about the DIY process you mention SmC252.

Regarding light, afaik 10% loss/gain anywhere in the system means 10% loss/gain on the final screen image.

[Guy Grotke]

Yes, the right white coating can reflect a bit more light than many polished metal surfaces (especially chrome or stainless steel), but the problem is not the total reflectivity. It is the directions the reflected light goes: Start with a piece of paper and a mirror in a dark room. Then shine a laser beam at the paper. The red spot on the paper can be seen from every angle of a solid 180 degree arc, because the paper scatters the reflected light in all directions.

Then shine the laser beam at the mirror. All of the reflected light goes off in one direction, making a bright spot on the wall somewhere. That "bright spot" is thousands of times brighter than if you tried to use the paper as the reflector.

When we use a reflector in a projector, we need as much of the light as possible to go toward the LCD in a useful direction. If you powder-coat your reflector, then most of the light will not get to the LCD because it gets "reflected" in all directions.

Charlie10: The underlying coats of nickel (and maybe copper) are included in the silver plating quote. They always have to do that. Silver just won't plate onto aluminum or steel without them. But I don't think you need to plate the aluminum Ikea napkin holder. You can polish aluminum up to 95% reflectivity. Much better than stainless steel's 65%, and I think chrome is even lower!