Projection Brightness
There
is more to image quality than just resolution. Brightness uniformity is also
important. Uniformity is the percentage of brightness carried from corner to
corner and edge to edge of your image. A higher uniformity rating means better
consistency throughout your image. For the most consistent images, look for a
uniformity rating of 85% or better. Brightness is measured in a number of way,
most commonly ANSI lumens.
Measurement
Lumens:
A unit of measurement of the amount of brightness that comes
from a light source. The standard lumen rating of a data
projector is the average of photometer readings at several
points on a full white image on the screen. Technically, lumens
measure "luminous flux." A wax candle generates 13 lumens; a 100
watt bulb generates 1,200. All of the specifications on our site
are in ANSI Lumens, ANSI or American National Standards
Institute is a standardized measurement system that can be used
to compare projectors.
Foot-lambert:
Measurement of light emitted or reflected from
a surface. The higher the rating, the brighter the picture. One foot-lambert is
equal to the reflected light radiated by one candle over a one-square-foot area.
Lux:
The International System unit of illumination,
equal to one lumen per square meter. Also called
candle-meter (cd/m²), Primarily used for projectors with lower lumen output.
|
LUX =
|
Projector Light output
(ANSi
lumens)
|
x reflective Screen gain
|
|
-------------------------------------------
|
|
Screen area
(square meters)
|
|
Luminance |
Abbr. |
Example |
|
0.00005
lux |
50 µlx |
Starlight |
|
1 lux |
|
Moonlight |
|
400 lux |
|
A brightly lit office |
|
400 lux |
|
Sunrise or sunset on a clear day. |
|
1000 lux |
1 klx |
Typical TV studio lighting |
|
32000
lux |
32 klx |
Sunlight on an average day (min.) |
|
100000
lux |
100 klx |
Sunlight on an average day (max.) |
In order to select how bright a projector you will need,
three factors need to be considered::
-
Room
brightness (ambient light)
-
Screen
size
-
Type of presentation
How Bright Should Your Image Be
"Sufficiently
bright" has been defined by Society of Motion Picture and Television
Engineers (SMPTE) in standard 196M as 12-22 footlamberts (41 - 75 cd/m2),
though often 16 footlamberts is taken as the nominal goal.
However, this standard was developed for movie theaters with full light
control. In a room with ambient light, this level of brightness may be
insufficient. It can be seen that as new technology
is introduced image brightness increases along with peoples
expectations. As a comparison:
- CRT TV
measures approximately 50 footlamberts (200 cd/m2) [and peak
luminance can be much higher],
- LCD TV
approximately 117 footlamberts (400 cd/m2)
- Plasma TVs
approximately 175 footlamberts (600 cd/m2).
- A cloudy day
outdoors is about 100 - 300 footlamberts.
It should also be
noted that the eye's sensitivity to colors is strongly correlates to
brightness, Hence, increasing the brightness of the image gives it a
more vibrant look, thanks to the better perceived colour saturation.
Room Brightness
Firstly I'd like you to consider why commercial cinemas are dark? Its because
even the brightest commercial projectors and TV's for that matter, Do not like
light! No matter how much money you are willing to spend if you want to improve
your image greatly, reduce the ambient light. This will maximize your
projectors potential and allow you to use a lower lumen projector and achieve
the same result. the other positive is that most high lumen projectors have a
shorter lamp life around 1000Hrs.
Many
sales staff say "You can watch
it in daylight"
Ok yes you can, but
Lumens or brightness can only help the bright
part of the projected image,
blacks in the image are not projected, light is switched off. If you watch in
daylight the dark areas of the image which are not projected will look grey and
washed out. If you have no option but to project in a lit room, you will need
the extra brightness and a higher contrast ratio.
If your room is very well lit, such as full fluorescents, you will need more
lumens. If the room were to have half of its ambient light, you would need half
the lumens. Rooms with minimal lighting will require a far less powerful
projector which saves you money.
Screen Size
The
bigger the screen, the more lumens you will need. If you double the screen size
- say from 60 in. diagonal, to 120 in. diagonal, you will need a projector with 4 times the
brightness. If you think of a torch shining on a wall the larger the beam the
lower the brightness. So a good idea is to work out the size of the image you
want. This is not just as big as the wall. As a rough guide remember that you
should be at a distance from your screen less than 1.5 times its diagonal for
that real cinema feel.
Type of Presentation
If you are presenting photos
or video quality images where colour accuracy and contrast is important, you
will also need a projector with more lumens. Its also important to consider the
size of the room - the area that the light will be spread over when it leaves
the screen. Larger the audience the brighter the projector.
Brightness of projectors:
-
Less than 1000 lumens - these are bottom of
the lumens range and they are typically LED Projectors.
If budget is an issue there are many projectors in this range. At this level
image size has to be small and
ambient light has to be kept very
low.
- Most
projectors in this range are for Home Cinema. 1000
lumen machines are suitable for normal movie and
gaming projection
use, closer to 2000 Lumens would be recommended for 3D
projection. Ambient light should be reduced to improve image
contrast, although complete block out is usually not necessary
depending on the image size.
- this represents the
high-performance range of the portable and semi-portable projectors.
Products in this class are suitable for conference rooms and
classrooms. They offer more flexibility in terms of ambient room light,
since the image is bright enough for some ambient light without washing out
the image. They also offer more flexibility in terms of audience size since
they can illuminate a larger screen without much loss of image quality.
- the ultra-bright
projectors are in several performance classes unto themselves, ranging from
5500 up to 21000 lumens or more. They are used in a variety of large venue
applications, including board rooms, conference rooms, training rooms,
auditoriums, churches, concerts, nightclubs, Simulators
and so forth.
How bright
should your projector be for your room?
Below is a fast and easy
reference for you to use to help determine how bright a projector you need for
your room.
|
|
Zero ambient light- dedicated room |
|
|
Slight ambient light, dimmed lights, Curtains or blinds letting in light - enough light for people taking notes |
|
|
High ambient light - lights on (cloudy day) |
|
|
Full Daylight |
|
|
Not recommended |
|
4:3 Screen |
|
Brightness
Lumens |
Screen Size |
|
72" |
100" |
120" |
150" |
180" |
|
800 |
|
|
|
|
|
|
1500 |
|
|
|
|
|
|
2000 |
|
|
|
|
|
|
2500 |
|
|
|
|
|
|
3000 |
|
|
|
|
|
|
4000 |
|
|
|
|
|
|
5000 |
|
|
|
|
|
|
7500 |
|
|
|
|
|
|
10,000 |
|
|
|
|
|
|
12,500 |
|
|
|
|
|
|
15,000 |
|
|
|
|
|
We recommend the following lumen outputs:
|
Installation |
Brightness
Lumens
|
Resolution
|
|
Hall / Commercial Cinema |
12000
|
HD (1920x1080 dots)
|
|
Fixed |
5200-10000
|
UXGA (1600x1200 dots) - XGA (1024x768
dots)
|
|
Portable |
2500-5000
|
XGA (1024x768 dots) - SVGA (1024x768 dots)
|
|
Ultra portable |
2000-3000
|
XGA (1024x768 dots) - SVGA (800x600 dots)
|
|
Micro portable |
2500-3500
|
XGA (1024x768 dots) - SVGA (800x600 dots)
|
|
Home theatre |
1000-2200
|
Wide-XGA (1366x768 dots) - SVGA (800x600
dots)
|
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