Brightness is to video as subjective loudness is to
audio. Much as the ear to sound, the eye is not equally
sensitive to the entire bandwidth of light.
The human eye is very sensitive to the wavelength of green
light, less sensitive to red light, and even less to blue
Luminance is the objective directional intensity of
light. Luminance is to video as the objective decibel is
And as the audio decibel, the lumen, foot-lambert, and nit are
the measure units of luminance. The choice of
measurement depends on the type of display used.
The Peak Lumen
The lumen is to luminance as the decibel is to
sound. The peak lumen is a measure of video
& The Projector
It measures a projected centered test pattern of a white block
filling 10% to 20% on the projection screen. The balance
of the screen remains black.
The term LED lumen has been introduced to laser projector spec
The Laser diode light is LED
based. LED light produce a narrow light beam pattern
compared to the UHE-lamp.
LED lumen measurement accounts for this
regarding room lighting.
However, this does not affect
peak lumen projector measurement.
& The Projector
The peak lumen is limited to a small angle of projector
radiation. Because of this limitation, the American
National Standards Institute offers a more stringent useful
measurement, the ANSI Lumen. The ANSI lumen
specification averages several measurements taken at different
positions on the projection screen. As a reference, a
projector that produces 1200 peak lumen may only measure 200
ANSI lumen. This measure is similar to speaker
& The Projector & Screen
Home theater projector-big-screen enthusiasts are more
concerned about the level of light at the viewer than at the
screen. Projector luminance is useful. But
reflected luminance decreases as screen square footage
increases. Luminance also decreases as the distance
between the projector, screen, and viewer increase. The
ANSI lumen does not sufficiently facilitate the home theater
The Foot-Lambert (ft-L) offers a more useful practical
measurement. The Foot-Lambert is a factor of projector
lumens, screen gain, diagonal screen dimension, screen width,
screen height, and aspect ratio. ProjectorScreen.com
offers a website calculator. The calculator produces a
reasonable estimate of the projection system's luminance in
As a reference, the Society
of Motion Picture and Television Engineers (SMPTE)
recommends a level of 12 to 22 Foot-Lamberts with a goal
of 16 ft-L in a dark room. If a low level of ambient
light is unavoidable, then 30 to 50 ft-L is the
& TV Screen
The Nit is a measure of luminance from a direct view
television screen. For reference, NTSC TV studio
monitors were capable of about 100 Nits. HD and UltraHD
televisions are capable of about 400 to 2,000
Nits. One Nit is equal to approximately 3.426
projector ANSI Lumens.
Select this LINK
for additional ANSI Lumen to Nit
It's a Matter of Scale, Grayscale.
Accurate luminance reproduction precisely ascends, scales,
from absolute black to specified white light. An
accurate scale, or grayscale, generates accurate color much as
accurate audio frequency response generates accurate musical
Contrast ratio is the difference between the brightest and
darkest screen image. There are two types of contrast
ratio measurement -- dynamic and ANSI static. The
contrast difference establishes the dynamic range of luminance
plus shades of color.
The dynamic contrast ratio is the most quoted by
manufacturers, e-zines, and magazines. Dynamic contrast
refers to the deepest black versus the brightness white that a
television, studio monitor, projector/screen can display, but
not at the same time. Dynamic contrast is an all-on
versus all-off test. This simple test can generate
impressive numbers such as 20,000:1 or higher.
ANSI Static Contrast Ratio
The ANSI static contrast ratio uses a standardized
checkerboard test pattern of black and white rectangles.
The ANSI standard simultaneously measures the difference
between the darkest black and brightest white displayed side
by side on a projection screen.
A Contrasting Story
A friend shared the following story to put contrast
measurement into a real-world frame of reference.
He had attended an Imaging Science Seminar. During the
presentation, he observed that a colleague of the lecturer had
entered the rear of the room. The lecturer acknowledged his
colleague with a nod as he continued to speak until he
finished his point.
The lecturer then looked to his colleague and asked, "How did
you do?" His colleague answered, "300 to 1". The
lecturer responded, "No way!'. His colleague insisted,
"300 to 1". Again, the lecturer responded No way.
He then paused and said, "Not unless ... you turned off the
exit lights". Yes, his colleague admitted with a
grin. 300 to 1 was his contrast result.
The lecturer then turned to the seminar audience to explain
their exchange. His colleague had just completed the
calibration of a commercial digital theater projector.
300 to 1 referred to the ANSI static contrast ratio he had
achieved with the exit lights off. The lecturer then
said, "Given what you just heard, you should be asking, where
do contrast ratios exceeding more than 10000 to 1 come from?"
He explained that many projector manufacturers begin with a
measurement of light in an absolutely-dark room. Well,
there isn't any light. Then they turn their projector on with
the lamp gain set to its highest adjustment. Then they
measure the light at the projection screen. This non-ANSI
difference is their contrast ratio specification. The
seminar attendees then responded with a chorus of
groans. The point, be skeptical of contrast ratio
Have you ever heard the expression 'red hot' or
'white-hot'? Both have their origin in blacksmithing and
welding. As a welding torch heats a piece of iron, it
changes from black to red to white, to blue. This effect
is the basis for the concept of color temperature in degrees
Kelvin. 6500° Kelvin is the video color temperature
standard of white light. Film uses a white standard of
C.I.E. Color Chart
The C.I.E. is the international
organization of color specification. The range of
visible color, or color space, is the x, y, z, points of the
C.I.E. Color Chart.
It resembles a three dimensional cone -- narrow at the top --
wide at the base.
The chart's x and y points stake
the color points of red, green, and blue. All color is
more or less bounded within the area of the red, green, blue
The chart's z-axis, marks the
amplitude, or luminance, of the color.
Some refer to the z-axis as
brightness. But that's not correct. The z-axis is
luminance, the objective measurement of light.
Brightness is the subjective-response of the eye.
D65 point, near the top, equals 6500° Kelvin, the color
white. The z-axis lowest point equals black.
Points from black to D65 track the gray-scale