PR-655/670 User Manual
73
The Luminance Adaptor enables the PR-655 or PR-670 to measure surface luminance and radiance of backlit
sources (e.g. cathode ray tubes, fluorescent lamps and self-luminous displays) that can be placed in contact with
the rubber cup of the Adaptor. It can also be used to approximate the luminance of more distant sources,
averaged over a circular field. (The acceptance angle of the adaptor is approximately 12.5
at the half-power
points and 14
at the 10% response points. The measuring area is 0.52 inch (13.2 mm) in diameter when the
cup of the accessory is placed in contact with a Lambertian source.
Warning:
The LA-655 / LA-670 is not recommended for use when measuring LCDs as the act of
coming in contact with the device may distort the surface and yield erroneous
readings and may cause damage to the display.
1.
Remove the MS-75 Objective lens or other accessory by turning it counter-clock-wise.
2.
Install the Luminance Adaptor by screwing in clock-wise.
Do not over-tighten!
3.
From the
Instrument Setup
menu, touch the
▲
▼
icons adjacent to
Primary Accessory
until
LA-655
or
LA-670
appears.
4.
Make any other changes such as
Aperture
,
Sensitivity, Speed, Average
etc.
5.
Place the front surface of the rubber cup of the Luminance Adaptor in contact with the target. Make
sure it is within the lit area or the device.
6.
Touch the
MEASURE button
to begin a measurement.
I
LLUMINANCE
/
I
RRADIANCE
Illuminance is defined as the density of luminous flux incident on a surface, or light falling on a surface and is
calculated from
Irradiance (watts/meter²)
. Three factors help determine illuminance: the luminous flux of the
source, the angle of incidence of the light falling on the plane and the distance from the source to the measured
plane. Illuminance is given by
lux (lumens per meter²)
and
footcandles (lumens/foot²).
The relationship between
footcandles and lux is:
1 footcandle = 10.76 lux.
In the following example, the light falling on the measured
plane is the illuminance.
FIGURE 70 - ILLUSTRATION OF ILLUMINANCE
Source
Measured
plane
Distance
Lumens
