The Effects of Reflector Design and Lamp Orientation

[18wheeler]

ace uses a 7" LCD. the light beam will cover the whole LCD at fresnel's FL. for 15" you will need a condensor lens.

[blackout]

Originally posted by 18wheeler
ace uses a 7" LCD. the light beam will cover the whole LCD at fresnel's FL.

wow, ace is a lucky man! thank you it was my doubt

[Guy Grotke]

Ace just found an elliptical reflector and fresnel that matched his LCD size. If you are making your own elliptical reflector, then you can design it to match a particular fresnel for your LCD.

Lots of different shapes are possible, from curved saucer to deep dish, but it loses too much light if you make it too shallow. For any reasonable set of focal points, you just need to make it deep enough so the rays spreading from the second focal point will cover your condensor fresnel at its focal distance. I spent less than an hour just fooling around with some push pins, string, and ruler, and I came up with a perfect reflector design for a 15" LCD with a 330 mm fl condensor fresnel.

For anybody who doesn't know how to draw an ellipse: Tape a piece of paper to a soft board. Put two push pins or thumb tacks at the focal points you want. Make a loop of string that is larger than the length between the two pins, and put it around the two pins. Then you use the loop of string to guide your pencil to draw the ellipse. If you don't like the shape, change the pin distance or the size of the loop. Try it, it's fun!

[blackout]

i can draw it but i have no idea about how build it...i was thinking to buy a professional one (18wheeler knows =).
how sis you build it? which material?

[Rox]

yes, i also find this problem. I can draw 1000 of them but can´t do 1. any idea?

by the way, what do you think about doing a giant eliptical reflector? this way we can have a high precision eliptical reflector so the light efficiency would be the best.

And also if we design the reflector for our custom setup, there is no need of condenser, we can designe it with the output angle needed for our rear fresnell or lcd size.

Condensor lens does help when the solid angle of the rear fresnell is smaller than the solid angle the bulb is capable of outputing, but the bad side of using a condenser lens is that the arc would virtually look larger, then when fresnlls project it to the triplet, it can be as big as 5" arc lengh.

[Guy Grotke]

I didn't, but I have looked into ways to do it inexpensively. There are two potential reflector surfaces, aluminum or silver. Silver is the very best reflector there is. (Only about 2% loss.) There are many places that will silver plate anything metal for you, so you could form the reflector from any metal and then get it plated to make it highly reflective.

Aluminum is also a very good reflector, (About 5-10% loss.) It is also easy to stamp, cast, or machine, and then polish. There is one thread here about machining a reflector out of a solid billet:

Ellipsoidal reflector-building one

I have also seen some interest in making a stamping mold for a 1/8th section of a reflector. Then 8 identical pieces would include lips along the edges that you could rivit or bolt together to make the whole ellipse. Copper sheet might work better than aluminum, with silver plating after the stamping. (But much more expensive.)

I have done some sand casting, so that is what I would try: You make a prototype out of anything you can work to the right shape, then you use it to make a two-piece greensand mold. You pour molten aluminum into the assembled mold. Take the solid piece out and machine or grind it to the finished shape, followed by polishing. If you can make a prototype. there are many small local metal foundaries that can do the casting for you, along with any of the remaining steps. It is just a matter of how much to DIY versus how much to pay somebody else.

Anybody who wanted to go into mass production could get the cost down to just a few dollars each by using modern stamping or spin forming. The materials and forming are identical to the reflectors you see for light bulbs, and those cost less that $10 US at retail.

[charlie10]

Does anyone know roughly how much would it cost to silver-plate a stainless steel Ikea "Soare" napkin ring? It's about 5 inches wide and 20 square inches of inner surface area.

Of course, I only ask because I want to make my table-settings more elegant!

[Me2!]

In that case ask Martha

ask your local plater in the yellow pages. guess $10-15??

Is silver plating better than chrome plating? Chrome seems more mirror like.

[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.

[Guy Grotke]

When something is chrome plated, the chrome layer is so thin it is transparent. What you are seeing is the nickel layer underneath the chrome. That combination is much less reflective than silver. Aluminum is a much better choice than chrome. Even with the naturally-formed transparent layer of aluminum oxide on the surface, it is better than 90% reflective.

Maybe you could get something silver plated and then chrome plated over that to protect it? Ask a plating company...

I actually studied silver plating quite a bit before I had my stainless steel reflector plated: Silver tarnishes by combining with atmospheric oxygen. If you heat lightly oxidized silver, it reduces the silver oxide coating back to metalic silver. I think a spherical reflector right next to a MH lamp, may be one of the few places you can use unprotected silver: Every time you use your projector it should get rid of any tarnish.

When I was shopping around, I saw prices from $20 to $48 for plating something the size of a saucer. Some platers have webpages. Shop around, but make sure you get good quotes by describing your reflector size and material: Some materials require multiple layers of other metals before the silver can go on.