ASTM F2964-12(2020)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: F2964 − 12 (Reapproved 2020)
Standard Test Method for
Determining the Uniformity of the Luminance of an
Electroluminescent Lamp or Other Diffuse Lighting Device
This standard is issued under the fixed designation F2964; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
2.1 ASTM Standards:
1.1 This test method covers procedures for determining the
F2360 Test Method for Determining Luminance of a Mem-
uniformity of the luminance of an electroluminescent (EL)
brane Switch Backlit with Diffuse Light Source
lamp. While written specifically for the purpose of evaluating
F2771 Test Method for Determining the Luminance Curve
EL devices, which are intrinsically very uniform, it can be
of an Electroluminescent Lamp at Ambient Conditions
applied (judiciously) to the measurement of any diffuse,
essentially planar, light source. For specific purposes, it can be
3. Terminology
applied to partially assembled devices into which the illumi-
3.1 Definitions:
nation is installed (such as a membrane switch) as a diagnostic
3.1.1 luminance, n—measure of the brightness or luminous
for the performance of the entire device. In such a case it must
intensity of light, usually expressed in units of candelas per
be understood that the results pertain only to the partial
2 2
square metre (cd/m ) or foot lamberts. 1 fL = 3.426 cd/m .
assembly and will be modified as the further assembly pro-
3.1.2 luminance curve, n—a graphical representation of the
ceeds.
variation of luminance with time (implicitly under unvarying
1.2 The method is to take a 2-dimensional set of
operating conditions).
measurements, sampling the surface of the unit under test with
3.1.3 electroluminescent lamp (EL lamp), n—essentially a
appropriate density. The method is restricted to measuring
capacitor structure with phosphor and a dielectric sandwiched
luminance only, since variations in color will also show as
between electrodes, one of which is transparent to allow light
luminance non-uniformity especially in any photoptically cali-
to escape. Application of an ac voltage across the electrodes
brated measuring device.
generates a charging field within the phosphor, which causes it
1.3 The values stated in SI units are to be regarded as
to emit light.
standard. No other units of measurement are included in this
3.1.4 time to half luminance (THL), n—the elapsed operat-
standard.
ing time over which the luminance of a lamp maintained under
constant power will be reduced to half of its initial value.
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the 3.1.5 UUT, n—unit under test.
responsibility of the user of this standard to establish appro-
4. Significance and Use
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use. 4.1 Application of an EL lamp (or other diffuse lighting
source) to illuminate a device has a functional purpose and
1.5 This international standard was developed in accor-
must meet specifications to satisfy the functional requirements
dance with internationally recognized principles on standard-
of the device.
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
4.2 Illumination of the device or application can be affected
mendations issued by the World Trade Organization Technical
by variations in the quality, efficiency, and design of the lamp
Barriers to Trade (TBT) Committee.
and any attendant mounting or shading fixtures.
4.3 This test method addresses only the optical and visual
appearance of the lamp and not its electrical function.
This test method is under the jurisdiction of ASTM Committee F01 on
Electronics and is the direct responsibility of Subcommittee F01.18 on Printed
Electronics. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Sept. 1, 2020. Published August 2012. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 2012. Last previous edition approved in 2012 as F2964-12. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/F2964-12R20 the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F2964 − 12 (2020)
4.4 This test method is non-destructive.
4.5 This test method is described for application to the
illumination layer in which case the results apply to that layer
only. However, it may be desirable and practical to apply the
test to a further assembly or to a fully assembled device with
built in illumination. In such a case, the results refer specifi-
cally to the subassembly or the entire device respectively.
5. Interferences
5.1 State of Assembly—Tests on incomplete assemblies give
results appropriate to that state of assembly. Specifically, later
application of mounting hardware, baffling, or fixtures may
alter the results.
5.2 Filling of Aperture—Failure to fill the sampling aperture
of the photometer will bias the results in a way which is not
necessarily predictable.
5.3 Age of Device—Since every system of illumination
changes characteristics as it ages, it must be recognized that the
results apply to a particular interval in the lifetime of the
system. Characterization of the aging properties may be
addressed in a separate test method. (See for example Test
NOTE 1—A sequence of nine, non-overlapping measurements which
Method F2771.)
will reveal side-to-side, center to edge, and top to bottom non-uniformities
of luminance. The order of sampling is suggested by the numbers. See 5.8.
5.4 Perpendicularity—Since the angular distribution of
NOTE 2—Size for the sampling area (shown here as small rectangles)
emitted light can be altered by any material through which it
can be chosen to maximize significance by taking it to be large enough to
passes, it is important that the photometer be held perpendicu-
average over any intrinsic granularity of the lamp (such as phosphor
lar to the area to be sampled.
crystal size) and small enough to avoid overlap with its neighbor (and thus
remain independent).
5.5 Temperature—Since the performance of many light
FIG. 1 Suggested Organization of Sampling Points for Uniformity
sources can vary with temperature, it is important to allow the
Measurement
UUT to stabilize thermally, if necessary, and then record the
ambient temperature at which the measurements are made.
6. Apparatus
5.6 Power—Since the performance of many power sources
6.1 A working or mounting surface to hold and support the
can vary with temperature, it is important to allow the power
UUT and any supporting fixtures, providing electrical access to
supply for the UUT to stabilize thermally, if necessary, and
the termination region from which the EL lamp illumination is
then record the warm-up time at which the measurements are
to be powered and visible access to all regions of interest on the
made.
lamp at which the luminance is to be measured.
5.7 Ambient Light—Stray light sources will be detected by
6.2 A power supply providing appropriate, stable and ad-
the photometer and will affect the UUT luminance measure-
equate power to drive the illumination device(s) with appro-
ment. It is important to measure the ambient light before
priate connector(s). This should be specified as dc or ac, with
illuminating the UUT. This ambient light reading should be
voltage and power level given, and ideally should be switched.
zero or as close to zero as possible.
6.3 A calibrated device to measure surface luminance (or
5.8 Sampling Aperture—The sampling aperture (area of the
radiance). This is typically a spot photometer, with a fairly
UUT sample and over which luminance values are averaged by
compact sampling aperture (<1-cm diameter at the minimum
the measuring instrument) should be large enough to average
working distance). Output should be in foot lamberts (candela
over any intrinsic granularity of the UUT. This area should also
per meter squared). Alternatively, a radiometer may be used, or
be small enough compared with the overall size of the UUT to
even a video photometer, but cognizance must be maintained
allow multiple measurements to be made without the sampling
of the output units and calibration. Hereinafter we refer to this
apertures of adjacent measurements overlapping (at least nine
as the photometer.
measurements are recommended). If areas overlap, the indi-
6.4 A means to support the photometer at a fixed distance
vidual samples may no longer be considered as independent
and orientation to the emitting surface of the UUT.
samples. The decision to allow individual samples to overlap
or to remain physically distinct is one the experimenter must 6.5 A means to move the lamp and photometer relative t
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