A Rational Methodology for Estimating 

the Luminous Flux Based upon Color 

Primaries from Digital Projection 

Displays

Edward F. Kelley,

Karl Lang,

Louis D. Silverstein,

and

Michael H. Brill

NISTIR 6657

National Institute of Standards and Technology • U.S. Department of Commerce 

 
NISTIR 6657

A Rational Methodology for 

Estimating the Luminous Flux Based 

upon Color Primaries from Digital 

Projection Displays

Edward F. Kelley 

Optoelectronics Division 

Electronics and Electrical Engineering Laboratory 

Karl Lang 

Lumita, Inc. 

Louis D. Silverstein 

VCD Sciences, Inc. 

Michael H. Brill 

Datacolor, Inc. 

January 2009 

U.S. Department of Commerce 

Carlos M. Gutierrez, Secretary

National Institute of Standards and Technology 

Patrick D. Gallagher, Deputy Director

 
A Rational Methodology for Estimating the Luminous Flux Based 

upon Color Primaries from Digital Projection Displays 

Edward F. Kelley, Karl Lang , Louis D. Silverstein and Michael H. Brill 

ABSTRACT: A standard methodology exists for estimating the flux from front projection displays by 

sampling the projected illuminance of a white source signal. With the advent and use of white projection 

primaries, a dramatic increase in flux can be achieved over the combination of red, green, and blue 

primaries alone. However, when a white primary is used saturated-color areas in an image are 

constrained to low flux levels relative to the display maximum and further undergo a perceptual 

compression in relative lightness. As a result, bright saturated colors cannot be rendered accurately and 

the appearance of full-color imagery is distorted. The display of color-accurate imagery does not 

generally use the white primary due to these problems, and thus there is a need for providing an 

equivalent flux measurement that will better describe the performance of all projectors when rendering 

full-color imagery. Background research and a method utilizing the source-signal color primaries are 

described. 

KEYWORDS: color accuracy; color output; color perception; color rendering; display measurement; 

display metrology; ICDM Display Measurements Standard; IEC 61947-1; ISO 21118; light output; front 

projector, flux measurement, projection display; sampled luminous flux measurement; white primary; 

white subpixel 

1. INTRODUCTION 

It has been observed that digital projection-display devices that include a white (W) image field 

or white sub-pixels in addition to the “standard” set of R (red), G (green) and B (blue) primaries can 

reduce the effective perceptual color gamut of projected information. [1, 2] This reduction is manifest by 

intended bright, saturated colors being constrained to low flux values, both absolutely and relative to the 

maximum white of the display. In such RGBW displays, the white “primary” darkens bright colors in 

two ways: (1) Relative to RGB displays, the illuminance of pure R, G, or B is low because the white 

primary must share the screen area or active projection time even when it is shut off, and (2) The visual 

system tends to adapt to the prevailing light so that perceived white stays the same; hence a highilluminance white will depress the perceived brightness of other colors. To see adaptation working in the 

reverse direction, one can make bright, saturated colors look even brighter and more saturated by 

artificially depressing the white in a scene. [3] Such variations in the effective perceptual color gamut of 

imaging devices such as projection displays may be readily characterized via perceptual experiments 

with human observers and can be estimated by the use of three-dimensional color spaces such as 

CIELAB or color appearance models such as CIECAM02. [4, 5] However, rather than address the 

subtleties of visual adaptation and its effects on perceived color, we choose a metric for RGBW displays 

that is based on simple optics, namely the sum of the illuminances of the full-on pure primaries R, G, and 

B. 

Whereas the color gamut reductions described above may not be important for the presentation of 

simple text and some graphics, a reduction in the perceptual color gamut can be highly objectionable 

when imagery is viewed. Thus, we consider here two modes of projector operation: a text/graphics 

mode and an imagery mode. The text/graphics mode can use a white primary component in addition to 

the RGB primaries. The imagery mode will use only the RGB primaries without any contribution from 

the white primary. We limit our discussion to front projectors that are intended to use standardized RGB 

signals such as the sRGB specification. [6] We want to be able to characterize the projected luminous 

flux of any projector in both modes. The use of the term “pixel” refers to the smallest division of the 

 1 
screen that can produce all colors. Whereas we are limiting this investigation to front-projector flux 

estimations, the thinking presented here can be extended to luminance measurements of both rearprojection displays and emissive displays that include white primaries or white subpixels. 

Figure 1. Color rendering with and without a white primary (left, original digital image; middle, 

photograph of screen with RGB projector without a white primary; right, photograph of screen with 

RGBW projector that includes the white primary). 

Figure 1 shows an example of a face pattern [7], a multi-colored ramp, and a test pattern based 

upon the Macbeth ColorChecker® [8] that depict the difference between the text/graphics mode and 

imagery mode in a projector that includes a white primary component. The left image is the original 

digital image sent to the projector. The middle image is a photograph of the screen with the projector in 

the imagery (RGB) mode, and the right image is a photograph of the screen with the projector in the 

text/graphics mode including a white primary component (RGBW). You will note that the introduction 

of the white primary tends to provoke a relative darkening of the colors compared to the white level 

along with shifts in the perceived hue and color saturation. These photographs can provide only 

approximations to how the projected images actually look, but they convey a reasonable impression of 

how the white primary influences imagery. 

To characterize the effective light output of digital projectors to be used for the accurate 

rendering of color imagery, and to compare the color-balanced performance modes of RGB projectors 

with those employing an additional white primary component, a method has been proposed in the 

literature by one of the authors that employs a nonatile (nine-tile) trisequence of RGB blocks—see 

Figure 2. [9] This method, which avoids the contributions from any white primary components, is 

 2 
compared with the full-white-screen method outlined in the existing measurement standards for fixedresolution projectors. [8] Rather than measuring a white screen, this method measures the three tiled 

patterns and combines the results to provide a flux estimate based only upon the RGB primaries without 

a white primary contribution. Why not just use a white screen for a projector’s imagery mode? To be 

sure that there is no white primary component present, the RGB patterns are used. Projectors often have 

several different modes of operation, and if they have a white primary present, the amount of 

contribution of the white primary can vary, depending upon the mode selected. For example, one digital 

projector has a mode called “sRGB” that also includes contributions from a white primary, whereas the 

sRGB specification does not account for any white primary component. The use of patterns consisting of 

only simultaneous RGB primaries on the screen is a safe method to assure that no confounding white 

primary component is present. The patterns are referred to by their diagonal color: NTSR refers to 

nonatile trisequence pattern with a red diagonal, NTSG, to green, and NTSB, to blue. 

Figure 2. Nonatile trisequence patterns for estimating projector flux without the contribution of white 

primary components. The rectangles are equal in dimensions ±2 px, and in each pattern, the nine tiles fill 

the entire screen. From left to right the patterns are designated by their diagonal color from upper left to 

bottom right, NTSR, NTSG, and NTSG, respectively. 

The following sections discuss the theory and apparatus used in making the measurements and 

the results of those measurements. The conclusion contains our recommendations. The appendix contains 

an example of measurement entries for the Display Measurements Standard document that is currently 

being developed by the International Committee for Display Metrology (ICDM). 

2. RADIOMETRY AND PHOTOMETRY THEORY 

Please note: Throughout this discussion, we speak of a measurement of the luminous flux (or 

spectral radiant flux) of a front-projector. Although we will usually refer to this as simply flux, it is to be 

understood that it is, in reality, a sampled illuminance (or spectral irradiance) measurement of the 

projected image multiplied by the area of the projected image to obtain an estimation of the luminous (or 

spectral radiant) flux. We will employ the correct terminology “flux” whereas the projection industry and 

existing or proposed standards use the coined term “light output” for measurements of the white screen 

and “color output” for measurements of the flux that use the nonatile trisequence patterns (Figure 2) 

where any white primary component and other complications are avoided. For reference, Table 1 lists the 

variables and symbols used in this document. 

In part, the method employed to measure the flux is based upon an existing standard. [10] That 

standard calls for a sampled measurement of the illuminance EWij of a projected white image in nine 

places at the center of rectangles that divides the full screen approximately (±2 px) into a 3 × 3 matrix of 

equally sized rectangles—see Figure 3. The estimated flux of the white screen ΦW is the product of the 

average illuminance and the measured area A of the image; 

 3 
∑=

=

3

1,

W W 9 ji

E ij

A Φ . (1) 

The illuminance (spectral radiance) measurement is made with the illuminance (spectral radiance) meter 

detector head in the focal plane of the projected image, and the illuminance meter must be cosine 

corrected. In the existing standard there are no position accuracy statements for the location of the 

illuminance measurements. Further, there is no specification for the calculation of the area when it is not 

perfectly rectangular, nor is it specified how accurate the cosine correction must be or even how 

accurately the illuminance meter must be calibrated. We will add the following requirements: 

Table 1. Variables or symbols reserved for use in this document (and possible future extensions) 

Variable or Symbol Definition 

D = R, G, B, C, M, Y, K, or 

W 

displayed color = red, green, blue, cyan, magenta, yellow, black, or 

white 

λ wavelength of visible light (our measurement range is 380 nm to 

780 nm) 

Φ, I, L, E, M luminous flux Φ (in lumens, lm), luminous intensity I (in candela, 

cd = lm/sr), luminance L (cd/m2), illuminance E (lux = lm/m2), 

luminous exitance M (lm/m2) 

Φ(λ), I(λ), L(λ), E(λ), M(λ) spectral radiant flux (W/nm), spectral radiant intensity (W/sr/nm), 

spectral radiance (W/sr/m2

/nm), irradiance (W/m2/nm), radiant 

exitance (W/m2

/nm) 

ΦD, ΦD(λ) luminous flux of color D, spectral radiant flux of color D 

ED, ED(λ) illuminance of color D, spectral irradiance of color D 

LD, LD(λ) luminance of color D, spectral radiance of color D 

A, Abox area of projected image, area of 1/3 screen-size box 

ΦRGB estimated luminous flux based upon a nine-point sampled illuminance 

measurement and a measurement of the area A of the projected image 

for which only the primary RGB pixels are employed with no white 

primary 

ΦW estimated luminous flux based upon a nine-point sampled illuminance 

measurement and a measurement of the area A of the projected image 

for which a white primary may be included with the RGB primary 

pixels in a white screen 

Eij, Eij(λ), EDij, EDij(λ) illuminance or spectral irradiance in general (Eij) or of color D (EDij) at 

any of the nine sample points with row i = 1, 2, 3 and column 

j = 1, 2, 3, where we use the standard matrix orientation with ED11

denoting the upper left, ED13 the upper right, ED31 the lower left, ED33

the lower right, etc. Summations indicated by the summation symbol 

with indices ranging from i, j = 1, 2, 3 to 3 will represent the usual 

mathematical arrangement where each index ranges from 1 to 3 

covering the entire matrix: 

∑ ++++++++=

3

ij 333231232221131211 xxxxxxxxxx

ji =1,

, 

where x represents any quantity. 

px abbreviation for pixel 

 4 
1. Position accuracy of illuminance measurement: The illuminance (irradiance) measurement region 

must be positioned within a circle of diameter 2.5 % of the minimum of the screen height or 

width that is centered at each of the 3 × 3 rectangles evenly dividing the screen. 

2. Cosine correction accuracy of illuminance (irradiance) meter: The uncertainty of the deviation of 

the cosine correction from ideal must be no greater than ±2 % over the measurement region of the 

centers of the 3 × 3 rectangles evenly dividing the screen. 

3. Illuminance (irradiance) meter accuracy: The relative uncertainty with a coverage factor of two of 

the illuminance (irradiance) meter must be 4 % or less and traceable to a national metrology 

institute (NMI). [11] 

All the measurements made for this document confined the position accuracy to within 2 % or less of the 

centers of the 3 × 3 rectangles. 

The area A is the area of the projected image on the projection screen (a plane in space and not an 

actual screen for all the measurement is made for this document). Because it is difficult to position the 

projected area exactly onto a specific size of screen, we must account for the actual projected size of the 

image. Given a general planar convex quadrilateral where the diagonals are specified by vectors p and 

q—see Figure 4—the area is given by half the magnitude of the cross product of the diagonal 

vectors: [12] 

zxyyxyxzzxxyzzy

zyx

zyx

zyx

( () () ) 2

1

2

1

2

1

e e e

eee

qp qpqpqpqpqpqp

qqq

A =×= ppp −+−−−= . (2) 

Assuming that the measurement plane is the x−y plane, so that all components in the z−direction are zero, 

this becomes 

( ) 2

1

2

1 A qp −=×= qpqp xyyx , (3) 

where x is the horizontal position (positive to the right) and y is the vertical position (positive up) with 

the origin at the bottom left of the measurement plane defining the imaginary screen in our case. To 

establish a simple estimation of the uncertainty in the area measurement, define a square with the same 

area as this distorted rectangle A = s

2

. Given that each side has the same uncertainty δs in its 

measurement, to a good approximation the relative uncertainty of the area measurement is 

δ = δ /2/ ssAA . (4) 

At the time the original standards were written and adopted with revisions by other standards 

organizations, white primaries (or, in fact, any additional primaries used in combination with R, G and 

B) were not commonly present in projection systems. Because of the different modes that can include the 

contributions of a white primary, we make the distinction between the projector flux ΦW with a possible 

white primary included and the projector flux ΦRGB that does not include a white primary. 

 5 
Figure 3. Patterns employed to establish measurement locations. 

p

q 

Figure 4. Area of projected image derived from diagonal vectors. 

There is a setup pattern specified in the existing standard [6], the intension of which is to allow 

the operator to adjust the controls of the projector to capture a specified range of gray shades. The 

objection to this pattern is that it has the dark gray rectangles embedded within a white background. Even 

for a young eye, this makes it difficult to see the dark grays owing to veiling glare in the eyes (or 

disability glare as we get older). We have employed a similar pattern (named SET01S50) that uses a 

50 % (gray level 127) background instead of white. It also includes 32-step ramps at the top and 

bottom—see Figure 5. [13]. A similar pattern SET01K (not shown here) has a black background that 

permits even better visibility of the dark levels. The actual pattern employed to check the projector setup 

for this document is shown in the bottom Figure 5. For most of the projectors measured it is possible to 

see all 32 levels in a user-configured mode. Often the white region is compressed for other modes so that 

not all levels are visible nearest the white level. 

 6 
0%, 5%, 10%, 15% (0, 13, 25, 38) ; 85%, 90%, 95%, 100% (216, 229, 242, 255)

85%, 90%, 95%, 100% (216, 229, 242, 255)

Center Bars:

0%, 5%, 10%, 15% (0, 13, 25, 38)

32 Gray Levels

32 Gray-Level Ends

32 Gray-Level Ends

32 Gray Levels SET04S50

Figure 5. Patterns employed to establish proper setup of the projector. The top pattern (SET01S50) is a 

modified version of the pattern specified in the existing standard document. [6] The bottom pattern 

(SET04S50) is the pattern employed in setting up the projectors for this document. 

 7 
3. MEASUREMENT APPARATUS 

The chosen size of the projected image is 1.2 m × 0.9 m, having an aspect ratio of 4:3. The area is 

approximately A = 1.08 m2

. A metal framework outlines the intended image area with black felt behind 

and above the framework to reduce contamination from scattered light. The projector rests on rails that 

are orthogonal to the image plane and at the bottom of the framework. In the corners of the framework 

are millimeter arrays that permit the accurate measurement of the projected image—see Figure 6. The 

uncertainty in the framework is estimated to be 2 mm. We estimate the uncertainty in the horizontal or 

vertical measurement of the projected image to be 6 mm to account for any imprecision in the sharpness 

of the focus of the projected image at the edges as well as accuracy in measurement of the placement of 

the image. Referring to Eq. (4), s = 1.039 m, and we will take δs = 6 mm. The resulting relative 

component uncertainty in the area of the projected image is estimated to be δA/A = 0.82 %. 

Figure 6. Laboratory setup. The projectors are placed on a rail system for positioning. The video 

generator is outside of the picture at the left. 

Figure 7 shows the spectral irradiance measurement of the center of the last of the nonatile 

trisequence patterns (NTSB). The spectroradiometer-integrating-sphere combination is positioned via 

x−y linear stages programmed to move the center of the sphere to the nine measurement points. The 

apparatus is operated manually. The procedure is as follows: 

1. The projector is placed on the platform, turned on, and fed a VGA (video graphics adapter) 

white full screen. 

2. The voltage levels of the signals are checked to be preferably within ±1 % of the desired 

0.7 V for the VGA signal. 

3. Various modes of operation of the projector are investigated to provide the brightest mode 

and, if the projector includes a white primary, the mode that avoids the white primary. 

4. The first, brightest, mode is selected. 

5. The projector is positioned to approximately fill the framework that defines the screen area, 

and the corners of the projected image are measured to calculate the actual area A of the 

projected image. 

 8 
6. The mode is viewed with a high-speed, low-resolution spectrometer to document the 

operation of the selected mode—whether it contains a white-primary contribution or not. (By 

this time, the projector has fully warmed up.) 

7. The grayscale and greenscale for the projector is then quickly measured with a simple 

luminance meter and a white plaque on the face of the integrating sphere at the center of the 

white or green image. This documents the electro-optical transfer function (affectionately 

often called a “gamma” curve) for the projection mode for a gray screen and for a saturated 

green screen—see Figure 9. 

8. The full-screen white and black is then measured and a full-screen (sequential) contrast is 

calculated with corrections for stray light, where the corrections are obtained with the aid of a 

projection mask (discussed below). 

9. The spectral irradiance (illuminance) of a white full screen is measured at the nine locations 

to provide a flux ΦW for a white screen. 

10. The spectral irradiance (illuminance) is measured at the nine locations for each of the nonatile 

trisequence patterns, and a flux ΦRGB is calculated avoiding any white-primary contributions. 

11. The next mode of operation is selected and steps 5 through 10 are repeated. Each mode that is 

selected for investigation receives the same documentation. 

For measurements using three nonatiling trisequence patterns, the equivalent illuminance Eij for any 

location i, j is a combination of the illuminances from each pattern at that location (see Figure 8): 

= + + EEEE BGR ijijijij . (5) 

The estimation of the flux ΦRGB is obtained by multiplying the average equivalent illuminance for the 

nine locations by the projected area: 

∑∑= =

= = ++

3

1,

BGR

3

1,

RGB ( ) 9 9

ji

ijijij

ji

ij EEE A E A Φ . (6) 

The flux ΦRGB should include no contribution from a white primary. For measurements using the white 

screen, the flux ΦW, 

∑

=

=

3

1,

W W 9

ji

E ij

A Φ , (7) 

may include contributions from a white primary, depending upon the mode of the projector. 

 9 
Figure 7. Measurement of the third nonatile trisequence pattern. 

Figure 8. Use of nonatile trisequence patterns to establish illuminances, shown for two locations. 

 10 
0.1

1

10

100

1000

0 50 100 150 200 250

Gray Level, n

Luminance, L(n) (cd/m 2) 

Figure 9. Electro-optical transfer function (“gamma” curve) for a projector with a white primary. The 

upper curve is for a white screen, and the lower curve is for a saturated green screen. 

3.1.1 DETERMINATION OF COSINE RESPONSE 

For these measurements, it is critical 

that the integrating-sphere detector exhibit a 

proper cosine correction over the range of 

angles for which it will be used. Figure 10 

shows a horizontal cross-section of the 

spectroradiometer peering into the 

integrating sphere and measuring the wall 

radiance on the opposite side toward the 

front of the sphere. A photopic photodiode is 

implanted in the wall of the sphere to 

provide a monitor to complement the 

spectroradiometer measurement result. The 

thick interior wall of the detector is made 

from sintered high-purity powdered 

polytetrafluoroethylene (PTFE). (The 

photopic photodiode is not cut through to the 

interior wall so that the diffusing properties 

of the wall material help make the 

photodiode more Lambertian in its 

response.) The left side of Figure 11 shows 

an EKE lamp mounted on a rotary stage with 

its rotation axis directly beneath the entrance port of the integrating-sphere detector. (A color meter is 

used instead of a spectroradiometer for this measurement only. The color meter was used to test various 

types of cosine detectors available to make this measurement.) The right side of Figure 11 shows the 

resulting normalized data as a function of the angle of the source from the normal of the detector. This 

provides us with an estimate of the relative uncertainty in the cosine correction of ucc = 0.38 %, rendering 

the detector suitable for use over ±30° that covers the angles for the nine measurement locations. The 

horizontal scan that is used here represents the worst-case uncertainty. Previous measurements show that 

a vertical scan with a horizontal detection (as is used here) shows much less uncertainty. 

Figure 10. Horizontal cross-section of integrating-sphere 

detector. A photopic photodiode is embedded in the wall 

without destroying the interior surface. When the 

spectroradiometer is used, a black-felt multilayer wrap 

surrounds the lens and near surface of the sphere to avoid 

any introduction of stray light.

 11 
0.85

0.9

0.95

1

1.05

-35 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35

Normalized Response

Angle θ, (°)

Figure 11. Apparatus using EKE lamp to determine the cosine-correction capabilities of the integratingsphere detector. A color meter is shown rather than the spectroradiometer that is used for the primary 

measurements. 

3.1.2 CALIBRATION OF INTEGRATING SPHERE DETECTOR 

A 150 mm diameter integrating-sphere source with a Ds = (51.06 ±0.12) mm diameter exit port is 

used to calibrate the integrating-sphere detector to provide measurements of spectral-irradiance and 

illuminance. Figure 12 shows the spectroradiometer measuring the radiance (luminance) of the exit port 

of the integrating-sphere source (left picture). That source is then used to calibrate the integrating-sphere 

detector with the spectroradiometer employed to measure the wall radiance (middle and right pictures in 

Figure 12). Three luminance meters are also employed to measure the center of the integrating-sphere 

source. The luminance-meter results are compared with the spectroradiometer results for each 

measurement-field-angle settings (0.125°, 0.25°, 0.5°, 1°, and 2°). The three luminance meters agree with 

a standard deviation of 0.29 %. The five spectroradiometer measurement-field-angle settings agree with a 

standard deviation of 0.19 %. However, the deviation between the luminance meter averages and the 

spectroradiometer luminance averages was udev = 1.9 %. 

Figure 12. Apparatus used to provide an illuminance calibration of the integrating-sphere detector. Left 

picture shows the spectroradiometer measuring the exit port of the integrating-sphere source; middle and 

right pictures show the source being used to calibrate the integrating-sphere detector with its 

spectroradiometer. 

The illuminance E at the entrance port of the integrating-sphere detector can be calculated from a 

knowledge of the luminance Lcs of the calibration source, the sizes of the ports involved, and the distance 

z between the exit port of the source and the entrance port of the detector: 

 12 
2

d

2

s

2

scs

RRz

AL E

++ = , (8) 

where As is the area of the source, Rs is the radius of the exit port of the source, and Rd is the radius of the 

entrance port of the detector; As = πRs

2

. During the calibration, it is not practical to reposition the 

apparatus to directly measure the luminance of the source. Rather, we rely on the source-monitoring 

photopic photodiode. The photopic photodiode on the integrating-sphere source is calibrated based upon 

luminance measurements over the exit-port area made by one of the luminance meters. The calibration of 

this source photopic photodiode is fm = 578.4 (cd/m2

)/μA with a relative standard deviation of 

um = 0.23 % (this uncertainty doesn’t include the uncertainty in the luminance measurement). The 

luminance Lcs of the integrating-sphere source for calibrating the detector is then given by 

Lcs = fm Jspd, (9) 

where Jspd is the source photopic photodiode current. The integrating-sphere source is placed 

approximately seven exit-port diameters from the detector port. The illuminance calculation represented 

by Eq. (8) is independently checked against an illuminance-meter measurement of the illuminance at the 

integrating-sphere-detector port and found to be within 1 % of the measured value. 

We anticipated receiving a spectrally calibrated source to check all the meters used in this 

calibration effort. However, the calibration source was damaged in shipment and could not be used. The 

individual luminance meters are considered to have a relative combined standard uncertainty of 

ulm = 2 % in measuring a tungsten-halogen illuminant. The relative combined standard uncertainty of the 

spectroradiometer making a similar measurement is estimated to be usr = 2 %. In order to compensate for 

the loss of the calibrated source, we will accept usr as the spectroradiometer component uncertainty, but 

we will add in the deviation udev and treat it as another independent component uncertainty. Small 

changes in position and focus of the spectroradiometer had no influence in its wall-luminance (radiance) 

measurement result when used to measure the wall radiance of the integrating-sphere detector. In fact, 

the detector configuration is remarkably robust. Several times the detector sphere housing was slammed 

into the framework when an error occurred in the positioning while the apparatus was being configured; 

each time the detector was re-configured and re-calibrated. Through all of this setting up and reconfiguration the calibration of the integrating-sphere detector survived at fd = 13.76 lx/(cd/m2

) with a 

relative standard deviation of only ud = 0.47 %. When in use, the luminance Ls of the interior wall of the 

integrating-sphere detector is measured. The illuminance E is given by 

E = fd Ls. (10) 

The factor fd is good for either photometric or 

radiometric quantities. 

3.1.3 MEASUREMENT OF SCATTERED LIGHT 

As shown in Figure 13, a projection mask 

is employed to estimate the stray-light contribution 

to the measurement result. [14] The stray-light is 

measured for all nine positions, averaged, and the 

relative standard deviation is calculated to be 

usl = 0.13 %. The computer screen is on during the 

course of these stray-light measurements as it is 

for the illuminance measurements in the ni

locations. 

ne 

Figure 13. A projection mask is used to determine 

stray-light contributions.

 13 
3.1.4 

ss)—see 

phere source as an added component 

uncerta

eral, a flux measurement Φ based upon an illuminance E measurement involves the area A

luminated: 

) 

volves the uncertainties in the illuminance E

measurement and the measurement of the screen area A: 

UNCERTAINTY 

We combine the above component uncertainties to obtain the relative combined standard 

uncertainty and relative expanded uncertainty with a coverage factor of two in Table 2. The type of 

uncertainty listed in the third column has two classifications, roughly speaking, Type A is an uncertainty

established by statistical means (a random effect in the current measurement process), and Type B is an 

uncertainty based upon other evaluations (a systematic effect in the current measurement proce

reference [11] for more details. We will treat the deviation between the luminance meters and 

spectroradiometer when measuring the center of the integrating-s

inty in our measurement apparatus—as explained above. 

In gen

il

Φ = E A. (11

The relative uncertainty δΦ/Φ in the flux measurement in

2 22

⎟ ⎝ Φ ⎠ ⎝ ⎠ ⎝ AE ⎠

⎞ ⎜⎛ ⎟ + ⎞ ⎜⎛ ⎟ = ⎞ ⎜⎛ δδΦδ AE . (12) 

From Eq. (8), the relative uncertainty in the illuminance measurement arises from its calibration 

2

geo

2

s

s

2

cs

cs

2

u

A

A

L

L

E

E

+ ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

+ ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ ⎟ = ⎠

⎞ ⎜

⎝

⎛ δδδ , (13) 

where 

⎥

⎥ ⎢⎣ ++ ds ⎦ ( RRz )

is a geometry component uncertainty, Lcs is the luminance of the calibration source, As = πRs

2

 is the area 

f the exit port of the calibration source with a radius of Rs (Rs = 25.53 mm, δRs = 0.03 mm; 

δAs/As = 2δRs/Rs = 0.23 %), z is the distance from the calibration source to the detector entrance

z ≅ 355 mm, δz = 0.5 mm), and Rd is the radius of the detector entrance port (Rd =

⎤ ⎢⎡ ++ = 2 22 2

2

d

2

d

2

s

2

s

22

2

geo 4 RRRRzz

u

δδδ (14) 

o

 port 

( 12.74 mm, 

δRd = 0

tforward, except for the luminance of the calibration 

source. From our discussions above, we can write 

.03 mm). The geometric component relative uncertainty is ugeo = 0.28 %. 

All the contributing uncertainties are straigh

2

d

2

m

2

sl

2

dev

2

sr

2

cc

2

⎝ Lcs ⎠

Here, ucc = 0.38 % is the relative component uncertainty from the cosine correction, usr = 2 % is the 

uncertainty in the spectroradiometer, udev = 1.9 % is the deviation between the luminance meters and th

spectroradiometer that we are adding in as another component uncertainty, usl = 0.13 % is the relative 

stray-light contribution being added in rather than serving as a correction, um = 0.23 % is the relative

component uncertainty in the luminance of the calibration source based upon its photodiode output 

current, and ud = 0.47 % is the reproducibility of calibration of the integrating-sphere detector. The result

of this

cs uuuuuu

L

+++++= ⎟

⎟

⎞

⎜

⎜

⎛ δ . (15) 

e 

 analysis is that the relative expanded uncertainty with a coverage factor of two is estimated to be 

6 %. 

 14 
Table 2. Relative uncertainties for flux calculation based upon sampled illuminance or irradiance 

measurements. 

1 Cosine correction contribution (ucc, no correction made for this) Type B 0.38 %

2 Calibration of spectroradiometer (usr) Type B 2.0 % 

3 Deviation between the luminance meter and spectroradiometer (udev) Type B 1.9 % 

4 Scattered light contribution (usl, no correction made for this) Type B 0.13 %

5 Contribution from calibration of photopic photodiode monitor used as a 

calibration lamp monitor (um) 

Type A 0.23 %

6 Repeatability in illuminance inference from wall luminance measurements that 

use the spectroradiometer and 150 mm diameter integrating sphere (ud) 

Type A 0.47 %

7 Source area relative uncertainty contribution (δAs/As) Type A 0.23 %

8 Geometrical component relative uncertainty (ugeo) Type A 0.28 %

9 Projection area measurement relative uncertainty (δA/A) Type A 0.82 %

Relative combined standard uncertainty: 3 % 

Relative expanded uncertainty with a coverage factor of two: 6 % 

3.1.5 DETERMINATION OF COMPOSITION OF WHITE AND PRIMARIES 

A high-speed, low-resolution spectrometer is employed to determine how each projector renders 

a white or primary-color screen in each mode of operation. In order to be sure that a certain projection 

mode does not add in a white primary component, the spectra of the white screen can be monitored in 

time. A collimated detector consists of a short-focal-length lens with a polished end of a 2 mm diameter 

plastic fiber-optic cable with black protective sheath placed at its focal point. The cable is routed to the 

spectrometer. The end of the cable at the spectrometer is elongated vertically and narrowed horizontally. 

A lens collimates the output of the cable into a diffraction grating, and another larger lens focuses the 

spectral image onto the detector array of the high-speed camera—see Figure 14. Figure 15 shows the 

results from the high-speed spectrometer when a white screen is measured within one frame. Figure 16

shows the spectra as measured with the spectroradiometer having a measurement-field angle of 2°

resulting in a full-width-at-half-maximum (FWHM) bandwidth of 20 nm. 

Figure 14. High-speed low-resolution spectrometer. The left image shows the collimated detector 

located at the base of the projector image. The right image shows the spectrometer with, from left to 

right, fiber input, collimating lens, grating, imaging lens, and high-speed camera. 

 15 
R 

G 

B 

W 

Figure 15. High-speed low-resolution spectrometer rendering of R, G, B, and W for a projector with a 

white primary. The R spectrum is made brighter to make it more visible. These spectra are obtained 

within one displayed frame of a white screen. 

0.00E+00

5.00E-04

1.00E-03

1.50E-03

2.00E-03

2.50E-03

3.00E-03

3.50E-03

350 400 450 500 550 600 650 700 750 800

Wavelength, λ (nm)

 Sphere Wall Radiance, L (W sr-1

m-2nm-1)

R

G

B

W

Figure 16. Comparison of integrating-sphere wall spectral radiance for R, G, B, and W for a projector 

with a white primary. These spectra are accumulations of many frames of R, G, B, and W screens 

respectively. A 2° measurement-field angle is used in the spectroradiometer, giving it a bandwidth of 

20 nm FWHM. 

 16 
4. MEASUREMENT RESULTS 

Five front projectors were measured; three included a white primary and two did not—see Table

3. The projectors not containing a white primary measured approximately the same for a white screen as 

for the nonatiling trisequence. The projectors containing a white primary showed dramatic increases in 

flux from the nonatiling trisequence to the white screen, as much as a 70 % flux increase. The expanded 

relative uncertainty with a coverage factor of two is estimated to be 6 % for these flux measurements. 

Table 3. Luminous flux Φ based upon sampled illuminance measurements.

Front 

Projector 

White 

Primary 

Available? 

(Y/N) 

ΦW

White Screen 

(lm) 

ΦRGB

RGB Nonatiling 

Trisequence 

(lm) 

RGB Color 

Contribution 

to Flux (%) 

White Primary 

Contribution to 

Flux (%) 

A Y 1471 464 32% 68% 

B N 1063 1067 100% NA 

C Y 1894 578 31% 69% 

D Y 1937 588 30% 70% 

E N 2027 2060 100% NA 

NA = not applicable

5. CONCLUSION 

We have seen how the introduction of a white primary component in digital front-projection 

displays may well produce a large luminous flux (“light output”) based upon a white full screen. 

However, when the white primary component is eliminated for the purposes of the display of accurate 

color image information, the resulting flux (“color output”) can be significantly reduced with only the 

RGB primaries being used. A method is needed to ensure that no white primary component is employed 

in the total luminous flux measurement of digital front-projection display modes used for the 

presentation of full-color imagery. This will help ensure that the luminous flux measurements are 

properly related to the available, effective perceptual color gamut of the display in color-critical imagery 

modes, as well as provide a more meaningful specification of projection display flux (light output) in 

these modes for both manufacturers and consumers. The luminous flux estimation based upon the 

illuminance measured from the nonatile trisequence patterns are found to be a meaningful and reliable 

means of characterizing the flux available in color-critical modes from all digital projectors, including 

those that use a white primary component to enhance their flux (light output). 

6. APPENDIX: EXAMPLE OF MEASUREMENT PROCEDURE ENTRY 

In this section we provide examples of various measurement methods as they might be 

contributed to the upcoming International Committee for Display Metrology (ICDM) document, Display 

Measurement Standard (DMS). It is important to note that the philosophy of the ICDM DMS is that the 

included measurements represent a buffet of measurements where we can pick and choose as we wish; 

no specific measurements are required. Section references and pattern references in these examples are to 

sections and patterns in the DMS document. 

 17 
6.1 FRONT PROJECTOR MEASUREMENTS — INTRODUCTION 

We consider the measurement of front projectors and 

front-projection screens in this section. Often, illuminance 

measurements are performed on such projectors. We speak of 

illuminance measurements throughout this section, whereas 

we could equivalently consider irradiance measurements 

instead—the reasoning is the same. 

6.1.1 DETECTOR UNCERTAINTY: 

Detectors used (often illuminance meters) should have a 

relative expanded uncertainty of 4 % or less that is traceable to 

a national metrology institute. The deviation of relative 

spectral responsivity from the spectral luminous efficiency of 

the human eye for photopic vision (f1') must be 8 % or less. 

6.1.2 DARKROOM REQUIREMENTS: 

Even with black walls, a black screen, and careful control of 

any instrument lights (including computers), a projection room 

is not completely dark. Reflections of light off the screen (even if black) will bounce off the walls and 

apparatus to contaminate the illumination falling on the screen from the projector. Thus, rather than 

strictly requiring stray-light illumination to be below some minimum, we can attempt to make 

corrections for stray light as needed. The use of a black screen with stray-light corrections can even 

permit the use of a room with white walls. 

Figure 1. Projector placement. 

6.1.3 PROJECTOR PLACEMENT: 

The placement of the projector relative to the screen should be detailed in the manufacturer’s 

specifications. Often the lens axis of the projector will be orthogonal to the vertical line at the center of 

the screen and placed either at a level near the bottom or above the screen. The image plane is usually 

vertical, parallel to the x-y plane. The projector is usually placed on or attached to a horizontal surface 

parallel to the x-z plane. See Figure 1. 

6.1.4 VIRTUAL SCREEN: 

A virtual screen is a vertical plane in space where the projected image would be focused if a projection 

screen were placed in that plane. Instruments to measure the light are often placed within and behind the 

framework so that their detector inputs are along the image plane. See Figure 2. 

One way to provide a virtual screen is to construct a 

black framework to define a surface with black material 

provided behind the framework to reduce scattered light into 

the room. The face of the framework defines the virtual 

screen surface. Millimeter grids can be accurately placed in 

the corners of the framework in such a way as to permit an 

accurate measurement of the location of the corners of the 

projected image. The desired accuracy of the placement of 

the grids to define the projected image in this way is 0.02 % 

or less of the minimum of the horizontal and vertical size of 

the projected image; for a projected area of 1.333 m × 1 m 

this requires a grid placement accuracy of 2 mm or less. 

Figure 2. Virtual screen with black 

background. 

 18 
6.1.5 PROJECTION MASK: 

Projection masks permit the determination of the 

stray-light corruption of projection 

measurements made in darkened rooms. A 

projection mask is a thin matte-black disk from

1.5 to 3 times the diameter of the acceptance are

diameter of the detector. The projection mask is 

used to shadow the detector from the direc

from the projector and is placed from 30 cm to 

60 cm in front of the detector—the larger 

projection masks being place at a greater 

distance from the detector. With the projection 

mask in place, the detector output is a measure

the stray-light contamination from the roo

can be different for each pattern displayed. 

screens and a darkened room are preferred. See 

Figure 3. If a black screen is not readily 

available, then a darkened room will suffice. 

However, the projection mask has been found not to work particularly well in bright rooms such as 

bright conference rooms. 

a 

t rays 

 of 

m and 

Black 

Figure 3. Projection mask in darkened room for 

stray-light measurement. 

6.1.6 SLET—STRAY LIGHT ELIMINATION TUBE: 

Stray-light-elimination tubes (SLETs) permit 

the measurement of the projected illuminance 

by rejecting stray-light corruption even in 

well-lit rooms—see Figure 4. One version of a 

SLET is constructed with five frusta: Four are 

in pairs back-to-back, and one is at the end to 

prevent light scattering off the illuminance 

meter from reflecting back to the illuminance 

meter and corrupting the measurement. The 

entry frustum has a slightly smaller inner 

diameter than the next three frusta so that the 

light from the projector doesn’t illuminate the 

inner diameters of the second set of frusta—if 

at all possible. The interior of the tube and the 

frusta are all gloss black. The idea is to control 

the stray light to virtual extinction by multiple 

reflections rather than trying to diffusely 

absorb it. For clarity the interior of the tube is 

not shown in the bottom of Figure 4. 

If the SLET is constructed so that the 

illuminance meter must be tilted in the 

direction of the projector so that the illuminance meter is flat against the back of the SLET, then an 

angular correction must be made to the resulting measurement, ESLET, if it is required that the illuminance 

measurement, E, be made parallel with the image plane: 

Figure. 4. Stray-light-elimination tube (SLET) with a 

cutaway showing interior frusta. 

 E = ESLETcosθ, (1) 

where θ is the angle from the normal of the image plane. Simpler versions of the SLET offer only three 

or even two interior frusta along the tube with a corresponding possible increase in the admission of stray 

 19 
light. By sighting up the SLET from the illuminance meter position using your eye, it is possible to 

inspect for stray-light entering the SLET. Judicious placement of the frusta can virtually eliminate the 

stray light from the room. 

6.1.7 WHITE REFLECTANCE STANDARDS USED TO INFER ILLUMINANCE: 

White reflectance standards (we will refer to them as pucks here) are often made from sintering 

powdered material into a disk shape. Often their hemispherical diffuse reflectances are from ρ = 0.98 to 

over 0.99. Rather than the use of an illuminance meter, some have placed these pucks in the image plane 

and measured their luminance L in order to determine the illuminance E via 

ρ

L E π = . (1) 

Strictly speaking this is not correct. The use of a diffuse reflectance value of, say, ρ = 0.99 in Eq. (1) is 

true only for uniform hemispherical illumination. In general, it is not correct to use this relationship for 

the luminance meter and projector at various angles from the normal of the puck. These pucks are not 

perfectly Lambertian, as the use of Eq. (1) with the hemispherical reflectance would suppose. 

To use such a puck to determine the illuminance, the puck would have to be calibrated for the 

geometrical configuration in which it is used. For projection systems the reflectance factor R(θs,φs,θd,φd) 

would be required, where the source (projector) is at angles (θs, φs) relative to the normal of the puck and 

the detector (luminance meter) is at angles (θd, φd) relative to the normal—see Figure 5. Changing any of 

those angles can significantly change the value of the reflectance factor. Therefore, the correct 

relationship is 

),,,(

π ),,,( ),(

ddss

ddss

ss φθφθ

θ φ θ φ φθ R

L E = , (2) 

where the reflectance factor calibration properly accounts for the source and detector angles employed. 

Depending upon the angles used, the error in by use of Eq. (1) can be as much as 10 % or larger. 

For measuring full-screen contrasts with the luminance meter, the projector, and the puck at the 

same location for each 

measurement, the pucks can be 

useful. Under such full-screencontrast measurement conditions, 

the expression for the contras,t 

K

W

L

L C = , (3) 

holds true, where LW and LK are the 

luminance measurements using the 

puck at center screen. This assumes 

that the stray light in the room 

comes only from back reflections 

from the screen illumination and not 

from various sources of stray light, 

such as instrumentation lights or 

computer screens. 

Figure 5. White reflectance standard used to infer illuminance.

 20 
 21 

6.1.8 PATTERN GENERATION: 

It is strongly recommended that a calibrated video generator be employed whenever patterns are to be 

measured. If a computer output is employed, then the signal to the projector must be measured to assure 

it is correct—this is particularly true when analog signals are used. Any deviation from the appropriate 

signal standard employed must be noted. Pattern resolution (pixel array) from the generator should match 

the native resolution of the projector. Patterns are named and defined in Section ZZZ. 

6.1.9 DETECTOR COSINE CORRECTION: 

To measure illuminance in the projection plane, the illuminance meter must be kept parallel to the 

measurement plane and must be cosine corrected to within 1 % over the range of angles between the 

projection lens center and the measurement locations that are used. If this requirement is not met, then 

the cosine-correction error must be reported. Cosine correction means that for uniform illumination from 

a distant source, the illuminance E changes as 

E = E0 cosθ, (4) 

where E0 is the illuminance with the source in the normal direction of the illuminance meter, and θ is the 

angle of the source from the normal. 
6.2 AREA OF FRONT PROJECTOR SCREEN IMAGE 

DESCRIPTION: We measure the rectangular or quadrilateral area of a 

projected image from a front projector displaying a white pattern on a 

front-projection screen. Unit: m2

. Symbol: A. p

q APPLICATION: Front projectors. 

SETUP: The following icons are defined in Section 3.7 for any 

standard setup details: 

OTHER SETUP CONDITIONS: (1) The front-projection screen used 

(virtual or real) must provide a means to determine the location of the 

corners of the projected image to within a distance of 0.02 % of the minimum of the horizontal or vertical 

projected image size. (2) A native-resolution full-screen white pattern is required (pattern FW*.* or 

equivalent). (3) It is preferable that the projected image have an area of no less than 1 m2

. (4) Some 

projectors provide trapezoidal adjustments, but the image does not have to be perfectly rectangular to 

determine its area. A quality video generator is strongly recommended. 

Figure 1. Diagonals of a 

planar convex quadrilateral.

PROCEDURE: The procedure depends on whether or not the projected image is rectangular: 

1. Rectangular Image: If the projected white image corners define a rectangle, then make a 

straightforward measurement of the horizontal dimension H and vertical dimension V of the image. 

2. Nonrectangular Image: If the projected white image is not sufficiently rectangular, then determine 

the horizontal (px, qx) and vertical components (py, qy) of the diagonals of the projected white image 

(Figure 1): p = pxex + pyey, and q = qxex + qyey, where ex and ey are unit vectors in the horizontal 

and vertical direction, respectively. The measurement will require an accurate grid to locate the 

corners of the projected image. (If a virtual screen is used, then grid plates must be accurately placed 

in the corners of the framework.) Determine the (x, y) coordinates of the corners of the projected 

image. Our notation will be: Lower left is (xLL, yLL), lower right is (xLR, yLR), upper left is (xUL, yUL), 

and upper right is (xUR, yUR). 

ANALYSIS: If the projected white image is rectangular, then the 

area of the screen is given simply by the product 

A = H V. (1) 

If the projected white image is not rectangular, then the components 

of the diagonals are given by 

, LRULyLRULx .

LL,URyLL,URx

yyqxxq

yypxxp

−= −=

−= = − (2) 

Note that in Figure 1, qx is negative. The area is then given by 

xyyx 2

1

2

1 A qp −=×= qpqp . (3) 

REPORTING: Report the area in square meters as needed. 

COMMENTS: This method assumes that the edges of the projected 

image are straight lines. See Section XXX for measurements of barrel 

and pincushion distortions. A reference for measuring a convex quadrilateral area is 

http://mathworld.wolfram.com/Quadrilateral.html. 

—SAMPLE DATA ONLY— 

Do not use any values shown to represent 

expected results of your measurements. 

Nonrectangular Analysis and 

Reporting Example: 

(Virtual screen with corner grids 

with origin at the lower left corner) 

Corner x (mm) y (mm) 

LL -11 5 

UR 1321 1000 

LR 1307 13 

UL -18 997 

(px, py) = 1.332 m 0.995 m 

(qx, qy) = -1.325 m 0.984 m 

A = 1.315 m2

 1 
6.3 SAMPLED FLUX FROM PRIMARY RGB COLORS 

ALIAS: Color Output 

DESCRIPTION: We calculate the luminous flux from a front 

projector by use of sampled illuminance measurements of RGB 

primary colors and the area of the projected image so that the 

influence of white primaries (white image fields and/or white 

subpixels) are avoided. Unit: lumen (lm). Symbol: ΦRGB. 

APPLICATION: Front projectors. 

SETUP: The following icons are defined in Section 3.7 for any 

standard setup details: 

OTHER SETUP CONDITIONS: The illuminance measurements 

must be made in a room where the stray light is ignorable or can be 

accounted for as a correction. 

Patterns needed: (1) SET01S50 as in Figure 1, (2) AT02P to locate 

the centers of the 3x3 array of equal rectangles that defines the 

measurement grid (Figure 2), and (3) nonatile trisequence patterns 

(NTSR, NTSG, NTSB) consisting of three separate patterns with 

RGB 3x3 arrays (Figure 3). A video pattern generator is strongly 

recommended for the nonatile trisequence patterns in the native 

resolution of the projector. 

Figure 1. Pattern (SET01S50) 

to set up the front-projector. 

Figure 2. Pattern (AT02P) to 

determine detector positions. 

Figure 3. Nonatile trisequence patterns (NTSR, NTSG, NTSB, respectively).

PROCEDURE: Select the mode of operation of the projector to be measured. For each mode selected 

perform the following steps: 

3. Measure the area A of the projected image according to Section 6.2. 

4. If possible, by adjustment of the projector settings, ensure that all the central dark gray and light gray 

levels in pattern SET01S50 (Figure 1) are discernable. Report any noncompliance. 

5. Assure that the illuminance measurements are made at the nine centers of 3x3 equal (±2 px) 

rectangles to within a radius of 2.5 % of the minimum of the screen height or width; this is the 

measurement grid. The use of a pattern as in Figure 2 (AT02P) can be helpful in determining the 

correct measurement locations. 

6. Measure and record the illuminance of the three nonatile trisequence patterns (Figure 3) at the nine 

locations of the measurement grid. 

ANALYSIS: We use the matrix notation i, j, where ij = 11 is the upper left and ij = 33 is the lower right, 

to define the locations of the measurement grid—see Figure 4, i = row, j = column. The illuminance Eij at 

any location i, j is given by the sum of the contributions from each of the three patterns at that location: 

= + + EEEE BGR ijijijij . (1) 

 1 
The flux ΦRGB is given by the product of 

the projected area and the average 

illuminance: 

∑

=

==

1,

RGB ave 9

ji

Φ AE Eij

3 A . (2) 

REPORTING: Report the flux ΦRGB to no 

more than three significant figures (unless 

more can be justified by an uncertainty 

analysis). 

COMMENTS: None. 

Figure 4. Illuminance measurements of nonatiletrisequence patterns. 

—SAMPLE DATA ONLY— 

Do not use any values shown to represent expected results of your measurements.

Analysis Example: 

Pattern Illuminance, E (lx) Illuminance, E (lx) Illuminance, E (lx) 

ER11 = 260.1 EB12 = 67.0 EG13 = 1319.6

NTSR EG21 = 1521.9 ER22 = 323.6 EB23 = 65.8

EB31 = 70.8 EG32 = 1618.2 ER33 = 320.7

EG11 = 1409.0 ER12 = 301.5 EB13 = 61.9

NTSG EB21 = 67.6 EG22 = 1578.3 ER23 = 318.7

ER31 = 287.7 EB32 = 70.4 EG33 = 1455.8

EB11 = 63.0 EG12 = 1459.9 ER13 = 289.2

NTSB ER21 = 278.5 EB22 = 70.7 EG23 = 1407.6

EG31 = 1543.9 ER32 = 333.5 EB33 = 63.6

E11 = 1732.0 E12 = 1828.4 E13 = 1670.7

E21 = 1868.0 E22 = 1972.6 E23 = 1792.2

Illuminance at 

each location: 

E31 = 1902.4 E32 = 2022.2 E33 = 1840.1

Average: Eave = 1847.6 Area, A = 1.116 m2 (Section 6.2) 

Flux ΦRGB = 2061.9 lm 

—SAMPLE DATA ONLY— 

Do not use any values shown to represent expected results of 

your measurements.

Reporting Example 

Flux ΦRGB = 2060 lm (3 sig. figs.) 

 2 
6.4 SAMPLED FLUX FROM WHITE 

ALIAS: Light Output 

DESCRIPTION: We calculate the luminous flux from a front 

projector by use of sampled illuminance measurements of a white full 

screen and the area of the projected image so that the influence of 

white primaries (white image fields and/or white subpixels) can be 

included. Unit: lumen (lm). Symbol: ΦW. 

APPLICATION: Front projectors. 

SETUP: The following icons are defined in Section 3.7 for any 

standard setup details: Figure 1. Pattern (SET01S50) 

to set up the front-projector. 

OTHER SETUP CONDITIONS: The illuminance measurements 

must be made in a room where the stray light is ignorable or can be 

accounted for as a correction. 

Patterns needed: (1) SET01S50 as in Figure 1, (2) AT02P to locate the 

centers of the 3x3 array of equal rectangles that defines the 

measurement grid (Figure 2), (3) FW or a full-screen white pattern. A 

video generator that uses the native resolution of the projector is 

strongly recommended. Figure 2. Pattern (AT02P) to PROCEDURE: determine detector positions. Select the mode of operation of the projector to be 

measured. For each mode selected perform the following steps: 

1. Measure the area A of the projected image according to Section 6.2. 

2. If possible, by adjustment of the projector settings, ensure that all the central dark gray and light gray 

levels in pattern SET01S50 (Figure 1) are discernable. Report any noncompliance. 

3. Assure that the illuminance measurements are made at the nine centers of 3x3 equal (±2 px) 

rectangles to within a radius of 2.5 % of the minimum of the screen height or width; this is the 

measurement grid. The use of a pattern as in Figure 2 (AT02P) can be helpful in determining the 

correct measurement locations. 

4. Measure and record the illuminance of a full-screen-white projected image at the nine locations of the 

measurement grid. 

ANALYSIS: We use the matrix notation i, j, where ij = 11 is the upper left and ij = 33 is the lower right, 

to define the locations of the measurement grid; i = row, j = column. The flux ΦW is given by the product 

of the projected area and the average illuminance: 

∑

=

==

3

1,

W ave 9

ji

Eij

A Φ AE . (1) 

REPORTING: Report the flux ΦW to no more than three significant figures (unless more can be 

justified by an uncertainty analysis). 

COMMENTS: This measurement method is an adaptation of Electronic projection - Measurement and 

documentation of key performance criteria - Part 1: Fixed resolution projectors, International 

Electrotechnical Commission, IEC 61947-1:2002(E), 40 pages, first edition 2002-08. 

 3 
—SAMPLE DATA ONLY— 

Do not use any values shown to represent expected results of your measurements.

Analysis Example: 

E11 = 1732.0 E12 = 1828.4 E13 = 1670.7 

E21 = 1868.0 E22 = 1972.6 E23 = 1792.2 

Illuminance 

at each 

location: E31 = 1902.4 E32 = 2022.2 E33 = 1840.1 

Average: Eave = 1847.6 Area, A = 1.116 m2 (Section 6.2) 

Flux ΦWRGB = 2061.9 lm 

—SAMPLE DATA ONLY— 

Do not use any values shown to represent expected results of 

your measurements.

Reporting Example 

Flux ΦRGB = 2060 lm (3 sig. figs.) 

 4 
 5 

7. REFERENCES 

[1] D R Wyble and M R Rosen, “Color management of DLP projectors,” IS&T/SID 12th Color 

Imaging Conference, 228–232 (2004). 

[2] R. L. Heckaman and Mark D. Fairchild, “Effect of DLP projector white channel on perceptual 

gamut,” Journal of the SID, Vol. 14, No. 9, pp. 755-761, (2006). 

[3] R. L. Heckaman and Mark D. Fairchild, “Expanding Display Color Gamut Beyond the Spectrum 

Locus,” Color Research & Application, Vol. 31, No. 6, pp. 475-482, (2006). 

[4] Mark D. Fairchild, “Color Appearance Models, 2nd Edition,” West Sussex, England: John Wiley & 

Sons Ltd, (2005). 

[5] CIE Technical Report 159 (2004): A colour appearance model for colour management systems: 

CIECAM02. Note that CIE is Commission Internationale de l'Eclairage (International 

Commission on Illumination). 

[6] IEC 61966-2-1 Ed. 1.0, Multimedia systems and equipment - Colour measurement and 

management - Part 2-1: Colour management - Default RGB colour space – sRGB. 

[7] E. F. Kelley, “Plotting the Course of the Next VESA Flat Panel Display Measurements Standard,” 

J. Society for Information Display, Vol. 13, No. 1, pp. 67-79, January 2005. 

[8] Any commercial item referred to in this paper or presented in a photograph is identified only for the 

purpose of complete technical description. Such a reference does not imply recommendation or 

endorsement by the National Institute of Standards and Technology neither does it necessarily 

suggest suitability to task. 

[9] K. Lang, “Analysis of the proposed IEC ‘Color Illuminance’ digital projector specification metric, 

using CIELAB gamut volume,” Late-Breaking-News Paper Presented at the 15th IS&T/SID 

Color Imaging Conference, Albuquerque, NM, November 2007. 

[10] Electronic projection - Measurement and documentation of key performance criteria - Part 1: 

Fixed resolution projectors, International Electrotechnical Commission, IEC 61947-1:2002(E), 

40 pages, first edition 2002-08. This standard is an extension of older standards. The effort started 

with an ANSI (American National Standards Institute) standard [ANSI/NAPM IT7.215-1992, 

“Data Projection Equipment and Large Screen Data Displays--Test Methods and Performance 

Characteristics.”]. A historical note: Because of that original standard, the estimated flux came to 

be termed incorrectly “ANSI lumens,” a term that was not used in the document but became 

common around the industry. Such a term is not legitimate because ANSI is not the keeper of the 

lumen; hence, we discourage its use in any documentation or even informally. The measurement 

could properly be termed “ANSI flux” but not “ANSI lumen.” 

[11] For a discussion of the proper way to specify uncertainty see: Barry N. Taylor and Chris E. Kuyatt, 

Guidelines for Evaluating and Expressing the Uncertainty of NIST Measurement Results, NIST 

Technical Note 1297, 1994 Edition. 

[12] http://mathworld.wolfram.com/Quadrilateral.html 

[13] E. F. Kelley and J. V. Miseli, “Setup Patterns for Display Measurements - Version 1.0,” NISTIR 

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