The Effects of Reflector Design and Lamp Orientation

[juice_e]

cool, thats probably the most useful advice ive gotten on these forums

thanks

[Guy Grotke]

A while back I was checking a lot of "found items" like mixing bowls and ladles, to make a reflector. I connected a 6 volt flashlight bulb with about 10 inches of solid copper wire, up to a battery holder with two 1.5 volt cells. When I throw the switch, the bulb lights up, but not too bright to look at.

To check a bowl with this tool, I put the bowl on a table, and then laid the battery & bulb assembly on some books next to the bowl, used some masking tape, etc., so the bulb is held at the center of curvature of the sphere. Then I would move my head around to see if the reflection of the filament came back to the filament. If necessary, I would adjust the position of the bulb slightly and then try again.

If you can find a position for the bulb where the reflection is right behind the filament when viewed from all directions, then you have found a good spherical object.

This is a good test, since this "reflection back to the light source" mode is exactly how you use a spherical reflector in a DIY projector.

[Me2!]

Bodgy,

I thought you might repost the link using the http button...

Ill try to anwer from the specs you show.

No. The worst spec is the CRI of 65. This bulb will have a few colours that really spike and the rest will be very flat. It is possible that the spikes are at the 3 primary wavelengths of your lcd but that would be a real gamble.

Better to go with a 90+ cri bulb.

The 40mm arc wont be great either although if your lens and projector are BIG it wont be too bad. It really comes down to the angles.

[juice_e]

I have a m58 ballast i got for $30 .. 250 watt..... it seems like all the bulbs i can find for it are rated at 65 CRI. Are there any bulbs for the M58 ballast that has a higher CRI that anyone knows about?

[SmC252]

Originally posted by 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!

My personal experience with mirrors under $100 is that they created bad hotspots. I've burned my plant because of a hotspot it created. Going by reflectance, you are right. But that isn't all we are trying to do, we also want to evenly distribute that light onto the fresnal. Right?
Now, if we were using the dual condensor lense way, we'd want to focus all the light into the first condensor to then have it distributed evenly by the second one throwing at the fresnal (which may even be optional depending on condesor quality.) With this, there will be no hotspots no matter what and the most-even distribution I think we will ever get. If I can find a large condesor around 8-10" diameter, (For under $50) I am going that route.

And yes, chrome has even lower reflectance then stainless and aluminum. I wouldn't be surprised if you could get aluminum to shine over 70% with the right kind of work.

[SmC252]

Originally posted by Dazzzla
I don’t think powder coating will stand up to the heat from a MH lamp, unless you mean enamelling.

DJ

I know it will for a fact, I have used powdercoating on automotive calipers before. They glow white hot and have even eventually taken out powder coatings. I know it stands up to at least 1500f and below fine, but over that don't bother.

Originally posted by juice_e
I have a question about ballasts. I can get 2 x 250 watt mh ballasts for cheap. Could i wire them together in series and hook up 400 watt bulb? Is that do-able?

DO NOT combine two MH ballasts!! If you are not sure about how they work, they start up with a 10-15k volt charge then continue at around 3000-5000 volts after they are started. Several amps of current is on tap, 2-3 amps can kill. Combining two would give you TWICE as much power on startup, at least guaranteed to shorten the bulb life. And be careful these can END YOUR LIFE if something goes wrong. I have been shocked by a 175watt MV setup and it nearly knocked me on my ***. My arm was numb for a week, if you do try this please read up as much as you can. This may be doable with some ballast wire swapping, I will try to look into this as well for you.

[SmC252]

Originally posted by bodgy
can i get away with 40mm arc length? i've seen people do it... I'm just sick of trying to find a perfect lamp (hard in aust), and im thinking bout this one:

The Phillips HPI-T PLUS 400W
(from: www.lighting.philips.com...subtab=dimension )
Length: 285mm
Width: 46mm
Arc: 40mm
Bulb Shape T46
Bulb Finish CLEAR
Watt (W) 400
Volt (V) -
Cap Base E40
Color Temperature (K) 4300
Lumen (Lm) 35000.0
Beam Angle (o) -
Line Frequency (Hz) 50
Color Rendering Index (Ra) 65
Color Descriptions 643 COOL WHITE
Average Life Hours -

Does it look like it is capable?

Let me lay this on the table, a Mercury Vapor lamp fits in our Metal Halide ballast socket and works perfectly WITH A SMALL arc gap! I am pretty sure they are all under 20mm. Take a look around and see if this would benefit you any more then a MH setup.

[SmC252]

I just did some research, my 400watt MH ballast has a 4000-volt starting pulse and as far as I see (from other sources too) there is a 1:10 ratio on wattage to starting power with the MV/MH lights. HPS has a higher wattage starting pulse then any other does. (Didn't find exact numbers though.)

[Dazzzla]

I know it will for a fact, I have used powdercoating on automotive calipers before. They glow white hot and have even eventually taken out powder coatings. I know it stands up to at least 1500f and below fine, but over that don't bother.

You must be thinking of silicon based powder coating to with stand that type of temperature. Any thing over about 500°C will cause organic pigments to deteriorate. Have you got a link to the type that you are referring to? The common thermo-type powder coating will not stand high temps.

If you are not sure about how they work, they start up with a 10-15k volt charge then continue at around 3000-5000 volts after they are started. Several amps of current is on tap, 2-3 amps can kill.

I think that you will find that the operating voltage for MH lamps is around 90-150Volts. And yes it can still kill.

DJ

[Nads]

I am not an expert with this stuff, being a noob an all, but what about glass rod, like people make glass ornaments out of, surrounding the arc, and then bent towards a collector point and then melted together. Would this form a good light source or would it be k rap?. The thought occured to whilst making a shop light display using fibre optic light guide, in which i had 1 light source, but many fibre optic strands. In my thoughts you would end up with a single point light source, but can light be `bent` like this sucessfully?. What about glass cut to shape on the back and mirrored to reflect all the light back, or a lens which would be possibly a good shape, and that was mirrored on the curved side?