projector - how much light is too much?

Discussion in 'Archived Threads 2001-2004' started by Dave Getson, Jul 3, 2002.

  1. Dave Getson

    Dave Getson Stunt Coordinator

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    I've just started looking at projectors. I was looking at the Plus HE-3100. It only has 450 lumens so as far as I can figure out, you'd need a really dark room to appreciate it. It looked great when I was watching the demo movie on it, but the room was very very dark with no light coming in.

    My question is, with a projector with such little brightness, how much light can a room have before the picture begins to look unwatchable? Until I have a dedicated HT, I'm always going to be using a room with a window....
     
  2. Dean McManis

    Dean McManis Agent

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    Dave,

    Basically, the light that comes into any room reduces how good blacks and contrast is. With a projector that has higher light output, it won't make the blacks any darker, but it raises the overall picture brightness, which causes your eyes to "see" better blacks.

    I wouldn't be overly concerned about the low lumens for a room that you can control the light with curtains, but the image will wash out more easily with less projector light displayed.

    What I would be more concerned with are the other shortcomings of an older digital projector of the generation that put out 400 lumens.

    Often the resolution of the display was much lower at 640 X 480 (VGA) or 800 X 600 (SVGA) that show up screen-door pixel gap, whereas newer projectors are mostly XGA (1024 X 768) or higher.

    Also optics and bulb design has improved to provide better contrast, better color, longer bulb life, and the newer models have MUCH better internal scalers which provide a visibly better looking picture from regular NTSC video sources (VHS, DSS, DVD).

    The surprise is that often sale-priced, discontinued, older models are often within a couple hundred dollars of entry-level XGA models, which are brighter and have a visibly better looking picture.

    Research different models and shop around a lot, and judge with your own eyes.

    -Dean.
     
  3. Gabriel_Lam

    Gabriel_Lam Screenwriter

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    With 450 lumens, it really won't take a lot of ambient light to totally smash your contrast level. With the Piano, you have, effectively over the lifetime of the bulb, less than 325 lumens to work with. This is assuming:

    The 130 watt P-VIP bulb loses 20-25% of its max illumination pretty quickly, and stays near there until the death of the bulb. Almost all current bulbs (UHP, SHP, NSH, P-VIP) do this. Xenon bulbs are the only ones that drop 20% initially and then steadily fall until they reach the 50% illumination level near the end of life.

    450 minus 20% = 360 lumens
    450 minus 25% = 338 lumens

    Most projectors need calibration, and may lose upwards of 40% of max light output when properly calibrated. Let's say the Piano is incredible precise right from the factory, and only loses about 10% during calibration.

    360 - 10% = 324 lumens
    338 - 10% = 304 lumens

    With perfect lighting control, the Piano has a very good on/off contrast ratio of 700:1. This is really why people buy the Piano. With an on/off contrast ratio of 700:1 in a dark room (perfect ambient lighting control), with 324 lumens max, that means your blackest blacks are being hit with 324/700 = 0.462857142 lumens of light. Let's say you have one dim reading lamp on in the room that spills merely 5 lumens of illumination onto the screen. 329 (which is 324 + 5) divided by 5.462857142 (which is 0.462857142 + 5) = 60.22. This means with that in this example, with one small light on, your excellent 700:1 contrast ratio has now dropped to 60:1.

    Now, given, by the time the light hits the screen and bounces off, we should be talking in terms of lux, not lumens, but for our discussion, we're keeping it simple. You can do all the conversions if you'd like.


    One thing to keep in mind is our eyes have a sensitivity range of 10^6 (1,000,000), which is absolutely incredible. However our sensitivity to light is not linear, it's more logarithmic. Going from 450 to 900 doesn't "seem" twice as bright to us.

    If you can get away with a relatively narrow viewing angle, you can combat this problem by using a high gain screen. What these screens tend to do is reject ambient lighting and make light hitting the screen directly focus more for the people right in front. However, you have to deal with the problems of hotspotting, etc.
     
  4. Dominic Ryan

    Dominic Ryan Extra

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    That's one of the most informative posts I've seen in a long time Gabriel! [​IMG]
     
  5. Anthony F.

    Anthony F. Stunt Coordinator

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    Agreed! That was a great post. I've always wondered how that worked and whether I could get away with a cheapo projector--now I know better.
     
  6. Dave Getson

    Dave Getson Stunt Coordinator

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    Holy smokes. Gabriel, you have just proven to me yet again that the members of this forum are incredible. Thanks for all the information!!
     
  7. Gabriel_Lam

    Gabriel_Lam Screenwriter

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    Glad to have been a help. Honestly though guys, calculations aside, only your eyes will tell you what is sufficient for you. Your eyes are the ultimate trump card. If the numbers say no, but your eyes say yes, trust your eyes. It's much like finances. If your wallet says ok, but your wife says no, you know you're not getting it. [​IMG]
    I personally like really bright punchy pictures. They just give you a lot more flexibility, especially if you want to have a superbowl party or something. No one wants to watch the superbowl in complete darkness.
    I'm on a 3000 ANSI lumen projector (4:3 native) with 800:1 contrast. If we use the same assumptions, I have about 1518-1620 available lumens. If we have the same light on in the room, we're still talking roughly 215:1 to 230:1 contrast. Not great, but definitely watchable. For night time watching, I can simply flick on some bias lighting (dim, neutral D65 lighting that sheds light, but away from the screen), and the eyes will naturally balance.
     

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