Difference between revisions of "Projector notes"

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: or in practice, the output figure for a projector divided by the area you're shining on
 
: or in practice, the output figure for a projector divided by the area you're shining on
 
: It's the best indication of how bright something will look on a given area of screen/wall.
 
: It's the best indication of how bright something will look on a given area of screen/wall.
 +
  
  
 
In my experience, '''at least 80 lux above ambient brightness''' is barely enough for movies, more for crispness, and more for clear office presentations and such.  
 
In my experience, '''at least 80 lux above ambient brightness''' is barely enough for movies, more for crispness, and more for clear office presentations and such.  
  
Note that since brightness is an logarithmic sense, a multiple more doesn't hurt.
 
  
So once you settle on a purpose, setting {{comment|('can I close the blinds' / 'will there still be light bleeding in' / 'does my office brightness standard bother this?')}}, and a screen area, you can calculate the minimum amount of lumen you need.
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So once you settle on a purpose, you need to figure out two major things:
 +
: setting {{comment|('can I close the blinds' / 'will there still be light bleeding in' / 'does my office brightness standard bother this?')}},  
 +
: screen area
 +
With the combination you can calculate the minimum amount of lumen you need. (though note that since brightness is an logarithmic sense, a multiple more doesn't hurt.)
 +
 
  
 +
Moviewatching has somewhat lower demands than text/presentation does, because it's the extreme where you can black out a room for movie nights. Assuming you're otherwise in darkness, that 80-lux rule-of-thumb means ~200 lumen is barely enough for a 80-inch / 2-meter diameter screen.
  
One extreme is a small blacked out room that can seat at most a dozen people, meant for movie nights. Moviewatching has somewhat lower demands than text/presentation does. Assuming you're otherwise in darkness, that 80-lux rule-of-thumb means ~200 lumen is barely enough for a 80-inch / 2-meter diameter screen.
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And if you ''can't'' black out the room completely, or want to avoid a halfway worn lamp making things look washed out, plan for more than that 80 lux difference.
  
And if you can't black out the room completely, or want to avoid a halfway worn lamp making things look washed out, plan for more than that 80 lux difference.
 
  
  
 +
At the other extreme is an office room where there are no curtains, there is bright environment lighting that you cannot dim because of building design to regulations {{comment|(e.g. offices and classrooms)}}, ''and'' the screen needs to be so large that the back of the large room must still be able to the smaller text (so easily over 100"), then you need ''multiples'' more brightness than the movie-night case.
  
At the other extreme is an office room where there are no curtains, there is bright environment lighting that you cannot dim because of design to regulations {{comment|(e.g. offices and classrooms)}}, and the screen needs to be so large that the back of the room can still read the next (easily over 100"), then you need ''multiples'' more brightness than the movie-night case.
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Also keep in mind  that the perceived brightness is logarithmic, so it rarely hurts to err on the brighter side.
  
  

Latest revision as of 23:52, 3 December 2019

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)


Screens

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)

Brightness

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)

Short story:

  • Visibility is about
light per area, and
it being a decent amount stronger than ambient light
  • Lumen is (approximately) the amount of emitted light. You can consider it the amount of power, but corrected for the human eye (ANSI lumen refers to a more specific test, that is typically used for projector ratings)
  • Lux is lumen per area, specifically 1 lumen per square meter
or in practice, the output figure for a projector divided by the area you're shining on
It's the best indication of how bright something will look on a given area of screen/wall.


In my experience, at least 80 lux above ambient brightness is barely enough for movies, more for crispness, and more for clear office presentations and such.


So once you settle on a purpose, you need to figure out two major things:

setting ('can I close the blinds' / 'will there still be light bleeding in' / 'does my office brightness standard bother this?'),
screen area

With the combination you can calculate the minimum amount of lumen you need. (though note that since brightness is an logarithmic sense, a multiple more doesn't hurt.)


Moviewatching has somewhat lower demands than text/presentation does, because it's the extreme where you can black out a room for movie nights. Assuming you're otherwise in darkness, that 80-lux rule-of-thumb means ~200 lumen is barely enough for a 80-inch / 2-meter diameter screen.

And if you can't black out the room completely, or want to avoid a halfway worn lamp making things look washed out, plan for more than that 80 lux difference.


At the other extreme is an office room where there are no curtains, there is bright environment lighting that you cannot dim because of building design to regulations (e.g. offices and classrooms), and the screen needs to be so large that the back of the large room must still be able to the smaller text (so easily over 100"), then you need multiples more brightness than the movie-night case.

Also keep in mind that the perceived brightness is logarithmic, so it rarely hurts to err on the brighter side.


Lux brightness for various lumen ratings on different areas:

                lux on a screen with this diameter (assuming 4:3 ratio)

                  60"     72"          90"            250"
               ≈1.1m2   ≈1.6m2        ≈2.5m2          ≈10m2
 100 lumen        90     (60)         (35)            (10)
 200 lumen       180     120          (70)            (20)
 500 lumen       450     300          175             (50)
1000 lumen       900     600          350             100
2000 lumen      1800    1200          700             200 
3000 lumen      2700    1800         1100             300

Bracketed figures are too low for most purposes - and you may want to be more critical than me :)


For reference:

  • 0.1-1 lux is moonlight in its various forms
  • 1-10 lux is approximately twilight
  • 4-20 lux street lighting (varies regionally)
  • 50-100 lux is one or two regular lightbulbs in a hallway or small living room
  • 100 lux is a dark overcast day
  • 30-300 lux: the amount of sunlight that typically makes it into rooms, varying with window size and wall reflections
  • 300-500 lux are well-lit areas in offices, libraries, and such
  • 1000 lux is a brightly lit TV studio, or a regular overcast day
  • 10klux-20klux: outside areas on a bright day
  • 30klux is direct sunlight


Note that for many projector bulb types, brightness will decrease noticeably over its life (with some variation depending on type, make, and certification).

See also:

Sharpness, clarity

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)

A perception thing. Depends on:

  • resolution (often between 800x600 and 1280x1024)
  • light output
  • contrast ratio (mostly bound by technology)

Bulbs

Cable extension

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)


If you want the projector somewhere on the ceiling or otherwise away from the video source, you often want to extend the video connection. A few relevant notes:


VGA (as in 15-pin D-SUB)

  • VGA is analog transmission of a digital signal. Moderate signal loss mostly shows as smearing and ghosting, and at some point it will lose synchronization and stop working
  • The higher the resolution, the shorter the distance it carries well. You may find that 1600x1200 stops after 1 meter, 1024x768 carries okay on 10m, and 800x600 acceptably on perhaps 25 meters.
  • Shops tend to carry cables up to 3 or 4 meters. For longer cables you'll often need to look around online (up to perhaps 30 or 50 meters)
  • Connectors are points of loss, so use the fewest extension cables possible
  • VGA baluns (over Cat5e cable) can go further. Orders of magnitude: 800x600 over 400 feet (120m), 1280x1024 over 100 feet (30m).


HDMI:

  • Specs specify a maximum amount of acceptable signal loss, no maximum length
  • Decent quality cable can do (passive) extension up to perhaps 10 or 15m. Longer cables exist, but are unlikely to be certified. They may work for your specific situation
  • Repeaters can take you much further, so are usually the better choice for longer distances distances. Active HDMI repeater cables seem to do perhaps at most 20-30 meters at a time