[noah katz]

100 W light bulbs for less than a buck, 1750 L


------------------

Noah

 

[RobertWood]

Noah,


I'm not sure if reading that sobered me or makes me want to get drunk.


BTW, I'm in contact with another forum member who is wanting to take a stock overhead projector and

make it have much higher light output. He just found a source for

a 12,000 lumen metal hallide lamp that has an 8000 hour life span and

costs only $89.


Bob Wood



------------------

~~The Sultan of Cheap~~


[This message has been edited by RobertWood (edited 04-18-2001).]

 

[Frank Maiello]

Metal-halide lamps are designed for general lighting. They don't have the color-rendering ability needed for projection duty. They have very good watts-per-lumen ratings and respectable color-rendering compared to other HID lamps. If you look at a spectral-distribution plot, you'll see a lot of spikes, unlike the smooth curve generated by incandescent sources. Take a mercury-vapor lamp, add some chemicals (halides) and there you are! Also, every batch is diferent because it's nearly impossible to add the chemicals in the exact same proportions every time. Look at a commercial installation where lamps have been replaced, their color-temperatures will be different.


Oh, you'll need a ballast as well.


This isn't to say you couldn't design a projector around one. However, there's a reason they're not popular for that application.


Frank

 

[RobertWood]

Frank,


He is buying the ballast and it is costing $130 so he

will have only $229 in the lamp and ballast.

I thought I understood that some LCD/DLP projectors actually are equipped

with "metal hallide" lamps. Is that not correct?


Bob


------------------

~~The Sultan of Cheap~~

 

[rickforrest]

Bob -


Is this other forum member planning to "soup up" his overhead projector and then combine with an LCD panel on top for a cheap(ish) high-lumens home theater projector?


If so, tell us more. I love jury-rigging things. http://www.avsforum.com/ubb/smile.gif

 

[RobertWood]

That's what he's going to do, Rick.

He's ordered the lamp and ballast. When he gets it

all together he'll post and tell us how it turns out.


Bob


------------------

~~The Sultan of Cheap~~

 

[rschneider]

As a former employee of an audio visual rental company, we would use high intensity overhead projectors developed by 3M. Model 9550, if I remember correctly.


They we ideally suited for use with LCD panels. In addition to having brighter bulbs, the optics were a little more efficient and the fans were larger.


Since the combination of overhed projectors and LCD panels has fallen out of fashon, there are opportunities to pick them up realitivly cheap.(>$200) That might be an easier and cheaper route than trying to "rig" your own high output projector.


Even the best overhead projectors are still horrible at displaying video.


Good Luck on your project


Richard

 

[hsitz]

Richard - So far as I can tell, the only problems with overhead projectors displaying video are their lack of brightness and the crappy yellow-color 3000K whitepoint halogen bulbs most of them use.


I've considered the 3M 9550 and similar 4000 lumens projectors, and I'm willing to use them as a fallback position. They have enough brightness for me, but I'm not going to pay $10-12 bucks per bulb for crappy yellow bulbs with a life of only 50 (!!) hours. (That's the rated life for bulbs in the 5550 and similar 4000 lumens projectors.) That comes to $100 bucks for 500 hours worth of bulbs. I realize you can reduce light output and get double the life, but even double the life is bad and 4000 lumens is already on the low end of the brightness I need.


So if the retrofit gives me 4000 lumens of white light with reasonable color spectrum distribution then it will be a complete success. It will cure what I think is the main problem with video from overhead projectors: the yellowish image.


Also, I'm going to be running three or four projectors at one time. At a bulb cost of $10 for 50 hours that comes to a running cost of $.20/hour per projector with the ordinary halogen bulbs. Now consider the HQI metal halide retrofit: with bulb cost of around $100 per bulb and rated life of 8,000 hours, that comes to a running cost of just over a penny per hour per projector.


Beginning to see the reason I'm going to all this trouble?: better color, much lower running cost. I still have ordinary 4000 lumens projectors as a backup option, but I hope I don't have to use them. -- Herb



[This message has been edited by hsitz (edited 04-18-2001).]

 

[noah katz]

Isn't a spiky spectrum just fine as long as there are some spikes in the red, green, and blue wavelengths? A 3-color laser source would have just 3 spikes.


I found it astounding that we perceive all colors from mixing together only 3, but then I learned that our eyes are actually RGB in operation, with 3 sets of color receptors (I forget if they're the rods or cones).


Actually, it's still amazing that our brains create the experience of all colors from a few.


------------------

Noah

 

[Frank Maiello]

Noah,


That's a really good point! Hmmmm...


So long as equal intensities of pure red, green, and blue are present, I suppose the theory stands. The projector would have to compensate to achieve the proper white-balance, but they're designed to do that anyway. Naturally, if the three wavelengths are already present at fairly similar intensites, little compensation will be needed, and you'd get the most light out of it. That said, if the RGB balance is way out of whack, I don't know if the signals modulating each LCD panel would would produce the expected results since you might already be clamping down on one of them considerably. (I'm thinking out loud here, sorry if this makes no sense or is totally incorrect. I'm an architectural engineer, so I'm way out of my area of expertise!)


I keep making slide/motion-picture projector analogies in my head. In this case, it's not accurate since we can tweak each color to our heart's desire. Using a poor CRI lamp in a slide projector just wouldn't work.


Frank

 

[hsitz]

I think I'm the forum member Bob's referring to. I am planning to see if the bulb retrofit will work with an overhead projector/lcd panel combination.


I may be able to test it this weekend, but perhaps not until next week since I don't have all the parts yet.


The bulb costs $89, ballast $112, and connector/socket $14. The bulb does put out around 12,000 lumens, and I'm hoping that will yield an overhead that puts out at least 4000 lumens, which might translate to a picture with LCD panel (which sucks lumens away) of 300 or 400 lumens. That would make me very happy, since the bulb has a rated life of 8,000 hours and the ballast can be used with another bulb.


It's true that the spectral distribution of the bulb has some spikes. But it's a fairly new technology HQI metal halide bulb that has a mostly smooth color spectrum with a much higher CRI than general purpose metal halides. Has a CRI (color rating index) of around 90 out of a theoretically perfect 100 as opposed to the 60 rating that is common for general purpose metal halides.


Also, the rated color temperature of the bulb I'm getting is 10,000K. I know, sounds really high. There are some available that have temp ratings of 6,500k but the people who are using those to light reef aquariums (a surprisingly big market for this kind of bulb) report that the 6500K bulbs are slightly yellow in comparison to the 10,000K and that the 10000K bulbs don't appear bluish. In any case, the screen I'll be projecting these things on has a slightly yellow tint so I'm figuring that will lower the white point a bit. And lots of projectors being used for HT have actual color temp ratings of well above 10,000K (even if manufacturer disagrees); just go to P. Putnam's site and look at his color temp measurements.


My planned application is not for home theater. I'm constructing a multiple projector simulator box for a computer driving sim. I want a picture that's as bright as possible while still being cheap. The three retrofitted projectors, if they work, will hopefully throw off an image of around 400 lumens of non-yellowish (important) light, and they will have bulbs with a rated life of 8,000 hours that can be replaced for $90.


Getting a cost effective solution is more important to me than getting something that's well-suited for HT. But I'm still hoping that it will be pretty decent. The total cost for the overhead projector/lcd panel/retrofit metal halide combo will be around $400-$600 per projecting unit. That's with only a 640x480 resolution, which is fine for my purposes. It might be possible to find a bargain basement LCD projector for that price, but not one that has bulbs replaceable for a reasonable cost.


Having said all that, I still have no idea whether my retrofit project will pan out. But I'll find out within a week or so. If not, I'll be unloading some stuff on eBay (which is where everything other than the bulbs came from anyway). -- Herb



[This message has been edited by hsitz (edited 04-18-2001).]

 

[ghibliss]

You need to very careful when testing the overhead projector and panel combination that the new lamp does not run excessively hot or you will permanently damage your panel in a very short period of time.

 

[hsitz]

Quote:

Originally posted by ghibliss: You need to very careful when testing the overhead projector and panel combination that the new lamp does not run excessively hot or you will permanently damage your panel in a very short period of time.

Yes, heat control is definitely something to watch. I don't expect it to be a problem with the components I'm using since the projector I'm retrofitting is a high-end one that was made to operate with an even higher wattage metal halide bulb than I'll be using (bulb life of 750 hours with $270/bulb), and the HQI bulbs I'm using are the most efficient temperature to lumens-wise that there are. I do know of one fellow who says he's been running a similar system with three 250 watt super-inefficient halogen lamps in a single projector. Now that's hot! And he says he hasn't experienced any problems. Still, we'll see. . . -- Herb




[This message has been edited by hsitz (edited 04-18-2001).]

 

[rickforrest]

Sounds exciting. As mentioned heat could be a problem. Here's a thought. Get some really big fans blowing on the projector. And the side benefit - the wind in your face will only add to that "in the car" feeling for an even more immersive experience! http://www.avsforum.com/ubb/biggrin.gif

 

[Frank Maiello]

Projectors use incandescent lamps (i.e. a glowing filament). They're halogen lamps, which means that there's iodine in the envelope that causes the tungsten to deposit itself back on the filament at high temperatures. Otherwise, the tungsten would "boil off" and deposit itself on the glass. It's called the Halogen Cycle, and is the reason that you should leave the lamp burn for a while once it's on. It gives the halogen cycle a chance to work.


Frank

 

[Frank Maiello]

MOST projectors, that is.