Series 426 Low Light Level Integrating Sphere Calibration Standard0 pages

OL Series 426
Low Light Level
lntegrating Sphere
Calibration Standards
GENERAL
The OL Series 426 Low-Light-Level Calibration Standard is
designed
for
accurately
calibrating
very
sensitive
microphotometers, image intensifiers, telephotometers, and
imaging
spectroradiometers
for
photometric
or
spectroradiometric response at moderate to extremely low
light levels. It serves as a highly accurate, large area, uniform,
diffusely radiating source with a near normal luminance that
can be varied over nearly 6 decades with essentially constant
color temperature.
The OL Series 426 consists of an Optics Head and a separate
electronic display console/power supply (OL 400-C Controller).
This enables remote location of either unit, which facilitates
alignment or positioning of the source with respect to the
device to be calibrated. The source module/optics head is
designed such that it can be configured with integrating
spheres having diameters of 4, 6, 8, 12 and 18 inches with exit
(radiating) ports of 1, 1½, 2, 3 and 6 inches, respectively.
OPTICS HEAD
The OL 426 is based on a dual integrating sphere design, with
the arrangement of these spheres in series. The exit port of
the first sphere, or primary sphere, produces a uniform beam
into the entrance port of the secondary sphere. A baffle tube
connects the exit port of the primary sphere to the entrance
port of the secondary sphere, and an aperture in the baffle
tube determines how much light is allowed into the secondary
sphere, thus the maximum luminance at the radiating port can
range over several decades depending on the size of the
aperture installed. The aperture is not used to determine the
true luminance at the exit port of the secondary sphere but
merely scale it by the desired amount. A precision silicon
detector-filter combination with an accurate photopic response
mounted in the wall of the primary sphere tracks the luminance
in the primary sphere at higher levels for accuracy purposes,
and the luminance display is scaled to indicate the actual
luminance at the exit port of the secondary sphere. The actual
luminance of the exit port is calibrated via measurements, and
then the monitor detector gain is scaled appropriately.

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The in-line sphere port concept with an intermediate spider
baffle provides exceptional uniformity in the near normal
luminance across the radiating port.
A shutter is located between the lamp and the entrance port of
the primary sphere. The luminance/ radiance output can be
switched between zero and any desired level without
adjustment or lamp changes.
An optional filter holder, mounted at the exit port,
accommodates alignment targets, filters, de-coupling diffusers
etc. for specific user requirements. Spectral shaping filters
can be utilized to simulate various sources such as Illuminate
A, B, C, D65, etc. In addition to luminance and color
temperature, the OL Series 426 can be obtained with
calibrations for spectral radiance over the 350 to 1100 nm
wavelength range.
CONTROLLER
The microprocessor-based OL 400-C Controller performs all
system interface and monitoring functions. An automatic ramp
up/down function eliminates potentially dangerous current
surges to the lamp. Luminance, color temperature, and lamp
current are displayed on a 2 line by 20 character alphanumeric
LED display, which may be turned off for low-light level
conditions. An 8-key keypad and main power switch are
located on the front panel for easy access to all system
functions. Luminance is displayed with 4 ½ digits plus
exponent in units specified by the user. As an option, the
display can be factory programmed to read in virtually any
pertinent units the user desires. DC current supplied to the
lamp has a 0.001 ampere resolution with a 0.02% uncertainty.
The controller computes the color temperature of the source
over the range of 2000 – 3000K. Software for remote
operation of the source is provided, allowing control of lamp
on/off functions and setting the lamp current (color
temperature) as well as readout of the photometer in any
preprogrammed optical unit.
An optional software
development kit is available for custom programming.

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As part of our policy of continuous product improvement, we reserve the right to change specifications at any time
Bulletin 136 / Rev 7-11
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