Guidelines / Manual
BTS256-LED Tester / Page 9
BTS256-LED Tester Description
Version 01.2009-01
Picture 9.1: BTS256-LED Base Design
The BTS256-LED tester is a compact size measurement
instrument to measure LEDs assembled and operated on
printed circuit boards (on-board LEDs). The design goal
was to create a light meter that could be brought to the ap-
plication instead of having to bring the DUT to the meter.
The end user can therefore measure his LED under real
application conditions anywhere.
Design (picture 9.1) and operating description:
The BTS256-LED device is designed with a compact size
integrating sphere
. The integrating sphere coating is Giga-
hertz-Optik’s robust ODM98 type OP.DI.MA. with a nearly
perfect diffuse reflection characteristic. To reduce risk of
contamination the sphere input is sealed with a 3D formed
window. The light input is a conical type adapter which can
be set over the DUT LED. To measure the total flux emitted
by the LED the surface of the LED must be within the coni-
cal adapter (picture 9.2).
To compensate substitution errors white LEDs act as auxil-
iary lamps. The LEDs are remote controlled to support the
substitution correction function included in the G.O.O.S.
software supplied with the instrument.
Gigahertz-Optik’s small footprint BTS256-P light sensor of-
fers a fine photometric matching photodiode for accurate
wide dynamic range flux detection. To work in concert with
the integral detector a compact low stray light design spec-
trometer is included. It’s 256 pixel CMOS sensor enables
spectral distribution measurements with a 5nm bandwidth
as recommended for color measurements. An ultra com-
pact remote controlled shutter is provided for on-line offset
compensation of the diode array through dark signal meas-
urement. For best signal to noise ratio the offset compensa-
tion is done in an on-line mode for each measurement with
identical integration time as that of the measurement
(picture 9.3). In applications where the flux level remains
the same over a constant integration time a offset constant
can be used. This reduces the measurement time since the
on-line dark signal measurement is omitted.
The spectral measurement data is displayed and used for
documentation of the spectral flux distribution in W/nm as
well as flux peak intensity wavelength, dominant wave-
length, xy and u’v’ color coordinates, color temperature and
color rendering index.
The spectral data is also used for on-line correction of the
spectral mismatch error of the photometric detector. This
spectral error is caused by limitations in current filter correc-
tion technology. By knowing the spectral sensitivity of the
photometric detector, the emission spectrum of the calibra-
tion lamp used for calibration and the emission spectrum of
the test sample (DUT) a correction factor can be calculated
using Gigahertz-Optik’s a(Z) method. Beside the on-line a
(Z) correction for each measurement a constant a(Z) factor
can be used for fast flux measurement with the integral de-
tector only.
To get more stable measurements in applications with
pulse modulated light or light with AC components the
Picture 9.2: Measurement Position
Picture 9.3: Spectral Measurement Mode
Picture 9.4: Pulse Frequency Synchronization
Time
In
te
n
s
ity
Frequency Synchronized Measurement Sequences
BTS-256P
LED Drive
Shutter Drive
µP
R
S
2
3
2
SMD without Lens
SMD with Lens
Time
Time
Equal Integration Time On-line Offset Mode
Fixed Offset Mode for Equal Integration Time
