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I'm starting to wonder about this after ordering a Da-Lite HC (.8 gain) 16:9 screen still boxed up in my family room (I've yet to purchase a projector). According to Da-Lite, you want to get between 20 and 50 foot-lamberts on this projection surface. Cutting to the chase, my size screen will fall at the high end of this range for a 1300 lumen projector (like an Infocus 350), and at the low end of this range for a 700 lumen projector (like an "old" Sony 10HT). Since projectors are only getting brighter, it seems to me that my situation will only get worse (> 50 f-l) with hot-spotting to come. Is there a simple answer here? Can I "dial down" the lumens on new projectors, or am I going to end up buying an "old" < 1000 lumens one? In case you're wondering, I had to get the screen now, but I started reading this forum in preparation for a future projector purchase (it will be either LCD or DLP--hence the "gray" screen). Thanks for your indulgence...
 

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I wouldn't be too worried. Most 1300 L PJs really aren't, and if they are, it's only on a new bulb. By the time you calibrate for video, you'll sure have less than 1300. If it seems too bright, you can reduce the contrast setting. Better yet, get a PJ with a low power mode, like Sony's "Cinema Black" mode. You can use the dark mode when the bulb is new and when the room is dark. If you want some lights on, or when the bulb has a few hundred hours on it, you can go to full powe.



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Steve
 

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I was just comparing our 800 lumen sanyo at work with our 1300 lumen infocus and I swear the 800 lumen Sanyo is a good bit brighter. I do remember reading that Sanyo is a bit more realistic on their lumen ratings. http://www.avsforum.com/ubb/smile.gif


I don't think that you need to worry about this one. Maybe if you had a 3000 lumen light cannon.


I don't hear anybody complaining about the brightness of their 2000 lumen G20s. http://www.avsforum.com/ubb/smile.gif


BTW how big is your screen???


Cameron


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You are not the only one with a screen and no projector. I have a Da-lite high contrast as well and am waiting to see what Sony has done with the 11vht. I was beginning to suspect the same thing. I saw a post saying that the Sanyo PLV 60 did not have as good blacks as the Sony. I notice also that to increase black level Sony lowers light output. I am beginning to think that the LCD technology maybe not be able to sustain decent blacks with the ever increasing light output. I have found that manufactures care first about sales. If super bright projector with ok blacks sell better than bright projectors with better blacks, you know which will be produced. I would suggest that you at least mount your screen and examine it. I have seen a few post about defective screens with complaints about creases,wrinkles and hot spotting. I think one guy shined a bright beam on his screen to test for hot spotting.


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The LP350 doesn't utilize its clear section in video mode so that is one reason why it doesn't make 1300 lumens.


A while back a Infocus person here on this web-site stated that the new infocus made a little less than 1000 lumens in computer mode and about 650 in video mode.


I think it is silent agreement between LCD manufacturers and DLP manufacturers that allow the DLP guys to inflate their lumens ratings, while the LCD guys inflate their contrast ratings.


Anyway, as far as an image being too bright, in general the most important thing for set-up is your projector's contrast ratio and your ability to control room lighting or overcome room lighting with a bright projector.


If your brightness is in a reasonable zone, the iris in your eye will do the rest.


I think a reasonable zone for pure white intensities is between 15 ft-Lamberts and 30 ft-Lamberts at the screen. Going below 15 ft-L and your colors won't have much pop to them. Going above 30 ft-L on digital projectors (which don't have an infinite contrast ratio) and your dark scenes will start to look washed out.


So, before we do a sample calculation, let's keep some other little facts in mind:


1. 1-chip DLPs don't make their brightness. They make about 70% of there brightness new and will probably average 50% during their lifetime.


2. LCD's do make their brightness new but you can go ahead assume they will average 75% during their lifetime.


3. If you do any color tweaking you'll lose some lumens. Let's say you keep 80% of the value before tweaking - a good guess.


4. screen gains are overly optimistic. Multiply any amount of screen gain above 1 by .7 (i.e. a 2.0 gain screen becomes (2.0 - 1.0)*.7+1 = 1.7).


A sample calculation goes something like this,


For a 2000 lumen LCD projector shooting on a 6' X 8' 1.3 gain screen you'll have the following peak intensity:


(2000 * .75 average over its life * .8 tweaking reduction * 1.20 screen gain) / 48 sq ft. screen surface = 28.75 ft-L peak white intensity.


That would be exceptable. Now if the LCD had a poor on/off contrast ratio, you might want to bring the brightness down with a Da-Lite HC or GreyHawk into the low 20's. This would help a little but the contrast ratio would still be somewhat of a problem.


Also, this analysis doesn't mean that you shouldn't get a bright projector. The bright projector will always help you overcome ambient light. It's just that it's on-screen intensity needs to be tamed with a grey screen (which will lower ambient light as well).


Good luck. Happy viewing.


-Mr. Wigggles




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[This message has been edited by MrWigggles (edited 07-04-2001).]


[This message has been edited by MrWigggles (edited 07-05-2001).]
 

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While looking at a Sanyo XP21N with Don Stewart, we looked at the contrast ratio and it came very close to the spec.




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Ken Elliott
 

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Ken,


Sorry, there are exceptions and the LCD side has been closing in on their claims lately.


-Mr. Wigggles


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[This message has been edited by MrWigggles (edited 07-05-2001).]
 

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Thanks for the insightful post, Wiggles.


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[This message has been edited by Bulldogger (edited 07-05-2001).]
 

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Mr. Wiggles,


Screen gains are accurate (to a certain precision). The top two screen manufacturers almost certainly do not inflate their gain measurements. You can depend on 1.3 gain being 1.3 gain. There's really no benefit or incentive to inflating screen gain values, the difference in cost between different gain surfaces is small (0 in the case of Stewart). Giving the consumer consistent results is more important.


Regards,


Kam Fung
 

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OK Sir Wiggles:


See if you agree with my math for the XP21N


6X8 screen = 48 square feet.


2500 lumens x 0.75avg x 0.8 tweak x 0.95Grayhawk divided by 48


= 29.69 lumens per square foot.


Now, perhaps one should use a neutral density filter with this projector, at least until the bulb ages, or the grey and contrast will be a problem? I believe these can be used to knock it down 20 percent.


Alternatively, what about the Da-Lite high contrast screen, with 0.8 gain? This reduces lumens to 25 per square foot.


Still too bright? How would this compare with your average RPTV? Your opinion, Sir Wiggles!


BTW, also my thanks for a really nice simple way for getting to brightness! http://www.avsforum.com/ubb/smile.gif


Dan
 

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Dan,


Thanks for the knighthood. I am sure at some point I had to bow before you to get it. I shall were it with pride.


The average direct view CRT is somewhere in the mid 20's ft-L while most RPTV's are mid teen's or low twenties.


Ken did a similar set-up to the one you mention hear and he thought the image was a little too bright. I think the da-lite might yield a slightly better image in this case however, do believe the Stewart to be a better screen.


Also bare in mind, these limits I suggest are soft. Don't go to lengths just to make these recomendations. For this reason, I wouldn't use the ND filter. Without it you'll have more light to overcome ambient light, a slightly sharper picture, and no potentially small loss in contrast do to reflections coming off the ND.


Good luck.


-Mr. Wigggles


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Sir Wiggles:


The important thing to remember is. . .


DON'T STAB YOURSELF WITH THE SWORD! http://www.avsforum.com/ubb/biggrin.gif


Thanks for your comments. You've really summarized this brightness thing nicely! Looks like I'm right on track!


Dan
 

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Ok, I'm going to jump in here. I am looking for a new projector also and am confused as to how many lumens to go for. I have a clarion shadowbox m1300 1.3 gain screen 100" diagonal. I can control light pretty well in my room but would like to be able to keep a little light on or let outside light in occasionally. any suggestions? My current projector is a sharp XV-H37VUA, 250 lumens so most projectors would be a lot better right? Also I have a question about Contrast Ratio's. I notice some of the brighter PJ's have low Contrast Ratio's. Why? Thanks, Matt.
 

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Mr.Wiggles(has iron cross-dont cross him!)

Say I like your numbers I would like to give some others.

Given that panel members say in great numbers a)they are in it for big screens 10ft+(60ft sq.+)b)they desperately need/use grey screens(like grayhawk)for lack of contrast(use .8gain)

Bill Cushman (WSR)measured Sanyo 2200 as net 583lumens(single lamp mode)after adjustments.So lets double that for 2000gross and it is 1166net.

FL= 1166x.8/60

=16FL.


Conclusion:we better have 4000 gross lumens on tap if want to go against Deronmoped CRT on 161inch screen(2.5 gain curved silver screen).It only gets better when you use screens like this with gains of 5-8.
http://www.avsforum.com/ubb/smile.gif Come on in Kam,the waters fine.


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Ron

"Your priorities will be different-its the weighting that counts!"
 

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You don't get something for nothing, at 2.6 gain the fall-off is quite extreme. The viewing cone, even with a curved screen is going to be quite small. Some people may not mind a little visible hotspotting, but I personally find it distracting when I see it. There's no question that even the real world lumen output of a digital projector will beat the real world output of a CRT (I doubt there's ever been a 9" CRT that tested out over 400 ANSI lumens). 2.6 gain is at the very top end of what is feasible for a uniform image using a compound curve screen, I find it hard to believe Deron is getting a hotspot-free image on his horizontally curved screen.


Screens with a gain of 5-8 are a really, really bad idea for home theatre applications.


Regards,


Kam Fung
 

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Screens of 5-8 gain are a bad ,bad idea.yes based on outmoded ideas and guidelines but that technology is changing.As you have said(Kam)we are seeing great advances in screen tech.

So for fun lets use your 3gain number as a temp upper limit.

this compares well to .8gain of competing units.Thats 4to1 in favour of CRT.Let me know of reasonable priced PJ(say $10K)that has 4times the brightness of a CRT(10K)with say 1250 peak lumens(thats how we watch video-not a slide or graphic frozen on screen(presentation style)

If the silence is deafening on this challenge I will not be surprised!
http://www.avsforum.com/ubb/smile.gif


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Ron

"Your priorities will be different-its the weighting that counts!"
 

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A killer projector under high ambient is about 3000 lumens SXGA with a 40% 100" grey screen.


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Ken Elliott
 

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Ron,


If you can get 1250 peak lumens out of a CRT, I will be very impressed. You find me a CRT that can do 1250 peak lumens (even if peak lumens are not the best way to measure brightness) in real life and I'll find you a $10k projector that can do 4x that! http://www.avsforum.com/ubb/biggrin.gif


There is not likely to be any kind of technology that can make 5-10 gain screens acceptable for home theatre use. To get that kind of gain you have to take light from the off-axis angles, ending up with a screen that is more reflective and a smaller viewing angle. There's no getting around this, the light has to come from somewhere. Not even a compound curved screen can give you a good image with that kind of gain. OTOH, if you move to lenticular rear screens, you can take light from the vertical angles and leave the horizontal angles untouched. However, these screens are very costly.


Regards,


Kam Fung
 

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Also keep in mind that the more light you throw at the screen, the more light that is reflected back into the room to bounce off the walls and ceiling and reflect back onto the screen to wash out the dark areas.


(Curved screens magnify this problem-- that's one reason it's so tough to shoot for Omnimax... the screen washes itself out!)


Decorating around the screen in dark, matte colors can help considerably and also improve perceived contrast.
 
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