Can someone explain to me WHY these DIY projectors are just not as bright as projectors you can buy in the shops?

What is the best final lumen output of a decent DIY projector compared to a commercial one?
I have heard they are about 800 lumens at best compared to 2000-3000 lumens for a commercial one.

I dont think its the bulbs, most commercial projectors use 175W (MH?) and DIYers use 250-400W!

Is it the LCD size? The light tunnel? Or what??

What are we missing here?

I'm not sure but I will take a stab at it.

LCD size. Less LCD, less light needed.
The LCDs are almost certainly manufactured just for projectors, thus allow more light to pass through the LCD.
More efficient use of reflectors.
Less glass (lens) to pass light through.
Engineers that make $100k or more a year.

i don't think that commercial pj is much more brighter (of course this would depend from case to case,type of lamp,lcd transmission coeff. etc) but if it is carefully done (maybe a higher color temp 6000k 7000K and experimenting with distances) the brightness is not anymore a problem.

Anyway it should be said that commercial pj use DLP technology which (if i'm not wrong) use mirror principle so the lamp is not placed behind a lcd as in diy one but it reflects the surface of a microscreen.
Instead on diy the lamp is placed behind so some light is lost due to a non perfectly transparent lcd.
The benefit of a diy is in higher resolutions,i would prefer a diy done.


regards

maXer

A big reason is that they use 3 LCDs while we obviously use just 1. Imagine a projector that just projected one giant pixel on the wall. That pixel from a DIY PJ would look like 3 vertical rectangles, one red, one green, and one blue. If we wanted to make that pixel as red as we possibly could we would have to completely shut off the green and blue rectangles so that no light passes through. Conversely a comercial PJ (since it has an LCD dedicated just for red) would project a big red square in this scenario. It's pretty easy to see how in this case we'd only have 1/3 the brightness.

Now think about a "white" pixel being projected. A DIY projector would also have 1/3 the brightness because each of the components to a white pixel (red, green, and blue) would each be 1/3 as bright.

So, right off the bat, all else being equal, our projections are 2/3 more dim because we only use one LCD.


After that, I'd say it boils down to size. Since the LCD is so small the reflector for the light can easily be the same size or bigger than the LCD. Since this is the case, they can use parabolic reflectors which are much more efficient than our spherical reflectors.


And last but not least, the companies that make comercial projectors lie. I would be willing to bet if we used the same methods to test comercial projectors as we do with our DIYs we would get much lower readings than what's stamped on the box...

Chances are that the bulbs are good at producing the red green and blue that the LCDs use, hence the expense. If bulb power isn't wasted by producing the wavelengths useless to a projector, there is a brightness and clarity improvement. Elken has discovered that from testing a ceramic lamp that is better at producing R, G and B.

Light Polarization recyclers. LCDs work by manipulating polarized light. That's why your LCD won't show an image if you accidentally remove one of the polarizers. Some commercial projectors use a special polarizer that lets correctly polarized light through but reflects incorrectly polarized light to a special polarization rotator optic (wave plate) that "twists" the polarization to the correct direction and reflects it back. Since a DIY projector doesn't recycle the incorrectly polarized light, it is just absorbed by the LCDs polarizer. Thats an approximately 50% loss.

Elliptical reflectors on the bulbs make a huge difference. Instead of only a small percentage of the bulbs light being used, like in our DIY projectors, the elliptical reflectors direct all of the light into a light tube. The light tube helps even out the light and directs it where it is needed.

Three monochrome LCDs instead of one RGB LCD. The light from the bulb is separated into red, green and blue light by special filters. The red light goes to the LCD getting the red portion of the video signal, the green light goes to the LCD getting the green portion of the video signal, and the blue light goes to the LCD getting the blue portion of the video signal. Since they are monochrome or black and white LCDs, there are no color filters on the pixels like there are on an RGB LCD. Most of the light hitting a monochrome LCD gets through, depending on the intensity of the color needed by any particular pixel. When the red portion of the lamp light hits an RGB LCD, the filters on the green and blue pixels absorb the red light. The red light only makes it through the pixels with red filters on them. So there goes 2/3 of the light right there, even if it is the correct wavelength range for making it through one type of color filter. The images from the three lcds are combined by a trichroic prism, and the light is directed into the projection lens.

The size of the LCDs. You don't need less light with smaller LCDs. The same amount of light has to go through any size LCD to get the same brightness for the same size image on the screen on your wall. What is important about the size of the LCD in a commercial projector is that it is very close to the size of the diameter of the projection lens. They don't use a fresnel lens to concentrate the light into a projection lens like DIYs do. The distance between the LCD and projection lens causes light loss, and the fresnel itself sucks up some light too. With tiny LCDs in commercial projectors, the light goes directly in a straight line from the LCDs(prism) to the Projection lens.

DLP projectors are another story.

Probably way more information than you needed, but there it is.

Tgreenwood

Very good points, thanks guys.

So are 7" diy projectors brighter than 15" ?
Is 7" the way of the future? (assuming you can get the resolution you desire)

Yes I read that companies exagerate thier pjs brightness.

Has anyone done real world tests of commercial and diy projectors side by side?
I would love to see the results of that. (or even just results from a diy pj)

Several members have used light meters to measure true lumen output on their projectors. Easy to find, just browse a bit.

Projector Central puts true lumen measurements in the reviews they post. Here's an example:

http://www.projectorcentral.com/optoma_hd70.htm

Cut and pasted from the above review:

"After exploring the options, we selected the settings most ideal for dark-room home theater -- low lamp, Cinema mode, with BrilliantColor at 5 or 6 and TrueVivid at 1. In this mode, our test unit measured 398 ANSI lumens. Given the contrast of the unit, this is easily enough light to fill a 120" diagonal 16:9 screen in a room with good light control. By changing over to "Bright" mode and switching the lamp to high, light output was boosted to 756 ANSI lumens. While this cuts down on contrast, it does provide a bright, colorful image that is ideal for video games in some ambient light. "

The manufacturer lists the lumens as 1000 ANSI. You can see that the true output is overstated a bit, and the low lamp mode is pretty similar to the light output of a decent DIY build.

Commercial PJ's no longer use metal-halide bulbs, but rather UHP mercury lamps with arc lengths of only about 1mm.

Here's a good explanation of the differences and reasons why commercial lamps cost more and are more efficient:

http://www.ercservice.com/lamps/philips/PhilipsUHPLamps.html

Philips has spent hundreds of millions $$$ developing these new state-of-the-art PJ lamps and the results are showing up in the latest commercial models.

300-400 lumens seems to be a standard minimum now for a commercial PJ in its best cinema mode. But some newer ones are putting out 2 times that amount as a minimum and sometimes even more...

Great info, thanks guys!

what the hell are you talking about?All commercial pj today use dlp.

READ THIS:

1.
THE SEMICONDUCTOR THAT CHANGED EVERYTHING


At the heart of every DLP® projection system is an optical semiconductor known as the Digital Micromirror Device, or DLP® chip.

The DLP® chip is probably the world's most sophisticated light switch. It contains a rectangular array of up to 2 million hinge-mounted microscopic mirrors; each of these micromirrors measures less than one-fifth the width of a human hair.

When a DLP® chip is coordinated with a digital video or graphic signal, a light source, and a projection lens, its mirrors can reflect an all-digital image onto a screen or other surface. The DLP® chip and the sophisticated electronics that surround it are what we call Digital Light Processing™ technology.

2.
DIGITAL LIGHT PROCESSING I: THE GRAYSCALE IMAGE


A DLP® chip's micromirrors are mounted on tiny hinges that enable them to tilt either toward the light source in a DLP® projection system (ON) or away from it (OFF)-creating a light or dark pixel on the projection surface.

The bit-streamed image code entering the semiconductor directs each mirror to switch on and off up to several thousand times per second. When a mirror is switched on more frequently than off, it reflects a light gray pixel; a mirror that's switched off more frequently reflects a darker gray pixel.

In this way, the mirrors in a DLP® projection system can reflect pixels in up to 1,024 shades of gray to convert the video or graphic signal entering the DLP® chip into a highly detailed grayscale image.

3.
DIGITAL LIGHT PROCESSING II: ADDING COLOR


The white light generated by the lamp in a DLP® projection system passes through a color wheel as it travels to the surface of the DLP® chip. The color wheel filters the light into red, green, and blue, from which a single-chip DLP® projection system can create at least 16.7 million colors. And the 3-chip system found in DLP Cinema® projection systems is capable of producing no fewer than 35 trillion colors.

The on and off states of each micromirror are coordinated with these three basic building blocks of color. For example, a mirror responsible for projecting a purple pixel will only reflect red and blue light to the projection surface; our eyes then blend these rapidly alternating flashes to see the intended hue in a projected image.

4.
APPLICATIONS AND CONFIGURATIONS



1-CHIP DLP® PROJECTION SYSTEM

Televisions, home theater systems and business projectors using DLP® technology rely on a single chip configuration like the one described above.

White light passes through a color wheel filter, causing red, green and blue light to be shone in sequence on the surface of the DLP® chip. The switching of the mirrors, and the proportion of time they are 'on' or 'off' is coordinated according to the color shining on them. The human visual system integrates the sequential color and sees a full-color image.

3-CHIP DLP® PROJECTION SYSTEM

DLP® technology-enabled projectors for very high image quality or very high brightness applications such as cinema and large venue displays rely on a 3-chip configuration to produce stunning images, whether moving or still.

In a 3-chip system, the white light generated by the lamp passes through a prism that divides it into red, green and blue. Each DLP® chip is dedicated to one of these three colors; the colored light that the micromirrors reflect is then combined and passed through the projection lens to form an image

The last time I checked, about two weeks ago, our local electrical retailer still carries LCD projectors. In fact 2/3rds of them were LCD.

DJ

dajyn

Thanks for finding and sharing that info...Ive found the full article here

http://www.extremetech.com/article2/0,3973,10084,00.asp

or

http://findarticles.com/p/articles/mi_zdex...10/ai_ziff15893

Sorry, I didn't read that whole quote, but I think the first line says it all... let me paraphrase:
All DLPs use DLPs.

Besides, most of what we've said above probably applies to DLPs as well. 'Cept they only use a single DLP chip with a color wheel to get the 3 different colors.

Here's a nice diagram showing how the Micro Lens Array on commercial projectors produces a brighter image by directing the light around the electrodes in the LCD panel/chip:

http://www.panasonic.com/business/projectors/lc_glossary.asp

BTW - Panasonic uses UHM lamps made by Matsushita (same company) that are presumably very similar to the Philips UHP lamps, but perhaps have surpassed them now in brightness.

The bottom line is that they are using more powerful lamps with more efficient reflector designs and more transmissive LCD panels/chips.

And tgreenwood touches on the inherent 3X advantages in brightness with a 3 chip LCD design, plus the other advantages with smaller LCD panels and components.

Yea there are loads of LCD pjs around, not just DLP.

I would personally buy an 3LCD pj, Ive heard DLPs can cause headaches and the rainbow effect for some people. Also I dont like the idea of the colour wheel, it could cause more noise and is liable to break.

I'm with you there trevas26, I saw my first dlp projector and right away noticed the rainbow effect and it is weird to me to say the least. If I don't move my eyes at all, I don't notice it. But as soon as I pan my eyes in any direction I see flashes of the colors making up the pixels. Especially if it's white text on black like movie credits, reading them feels horrible to my eyes. I read something about it though, that higher end models use 3 dlp chips dedicated to each color similar to the way lcd pjs do, except they use a prism to merge the images. This stuff is so damned interesting

My PJ is outputting around 450 lumens. That's more than the example listed above.

So we can be brighter than some but it takes some work.

If you compare DYI to LCD commercial and look at all the difference things the two things that will stand out are the triplet "F" value and the lamp intensity.

The triplet F is almost the most important thing of all that no one looks at. For two 40mm diameter triplets with two fl of 300mm and 150 mm the PJ with the 150 mm triplet can be twice as bright. Why? The triplet will have an F value twice as low.

300/40=7.5 V 150/40=3.75 for the shorter fl triplet.

To take advantage of the larger triplet a longer arc lamp could be used or a larger reflector can be used. The commercial PJ always go for the larger reflector setup because it is more efficient.

The other way to be brighter is by using a more intense arc. Wattage really means vary little, it is how intense the arc is that matters. What we are doing is making an 80mm light spot at the triplet which is an image of the lamp at the other end of the lens system. The more intense the lamp the more intense the spot at the other end.

After looking at hundreds of lamps a few things become clear. The more intense the arc the shorter the life if the lamp. The only deviation from this rule is the ceramic lamp which has about a 30% more intense arc with out having a shorter life.

The shorter the arc the lower the lumens efficiently of the lamp. My MHI 1200 watt lamp has around a 65 lumens per watt and a long arc lamp will have around a 90 lumens per watt, the ceramic looks really good with the highest efficiently.

Most PJ have a 2000 to 3000 hour life. If I had a triplet with the same F value as a commercial PJ and overdrive the lamp to get a 2000 hour life or use a HMI type lamp I could match the brightness of a commercial LCD PJ.

If I had a 550mm x 300mm triplet with a 17" LCD and a nice elliptical reflector and a 300 watt small arc HMI lamp we would be about he same brightness.

There is no magic here.

Some one said that the PJ no longer use MH but short arc mercury lamps I would like to say that all of our lamps mercury lamps. The UHP is a DC short arc lamp. We use A/C lamps. For light setups with ultra small arc's any arc movement will be seen on the screen because of the vary high arc magnification factor used by the light system so the pulsing of a A/C lamp will start to become a problem at some point as the arcs become even smaller.

DLP are just more efficient because they use no polarizer’s.

Lots of reasons as stated above.

Really though, there are a few key factors.

LCDs. We use general purpose LCDs. They're intended to be viewed directly, not used for projection. This gives us some disadvantage from the start. We can overcome this somewhat, but it's hard.

The smaller LCDs also allow the commercial projector to take more advantage of the square law. Because we use larger LCD panels, we NEED more distance between the LCD and the light source. For a 15" LCD, if the center of the collimator fresnel is 220mm away, the corner is 291mm away. (Basic pythagorus calculation) Apply square law to that, and the BRIGHTEST that the corner can be is about 57% of the brightness of the center, assuming no other inherent losses (which there are, because of the angle of incidence.) By contrast, a 1.5" LCD can be a mere 40mm away from the arc, and come up with much better vignetting numbers. Even counting the smaller area, the end result is a much greater ratio of lumens produced to lumens projected.

This is also why it is POSSIBLE to get more lumens through a smaller panel. It is not possible if you make everything the same, but because you don't have to make things the same, it becomes so. There is, however a price to pay, in that a smaller panel puts more stringent requirements on the lamp. This is why commercial PJ lamps cost hundreds of dollars and have much shorter life expenctancy than our lamps. So it's all about trade-offs.

Commercial projectors want small case sizes, which means small panels, close distances, and expensive, short-lived lamps. We WANT the small panels, but there are limits to what we can get that are still reasonable. (This is why the 10.6" HD panels were/are such a big deal.)

So basically, it comes down to commercial projectors having less loss due to square law than DIY. This allows them to put more lumens on the screen with less power dissipated. Greater efficiency and smaller size, but at a cost in limitations of the lamp itself.

DLP is a whole different animal, and there's no useful comparison. DLP is far more efficient, though because of the "colour wheel" it ends up losing some of it's efficiency gain by strobing the mirrors. (This is what results in some people getting "rainbow" effect from DLP projectors -- it creates the 'red' image, then when the wheel turns to the green filter, it creates the 'green' image, then the wheel turns, and it creates the 'blue' image, then back to red.) It's still very efficient, and can have amazing contrast ratios. But there is no useful standard of comparson between that and LCD technology.