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Bi-technology sensor light meter for high speed LED binning. Features: High spectral resolution, short measurement time (electronic shutter), high dynamic (filter wheel), Trigger input and output, entrance optic with diffusor for illuminance and spectral irradiance, CCT, CRI, color values, etc.


Requirements of a modern, versatile array spectroradiometer

There are many factors to be considered when assessing the suitability of array spectrometer systems for the absolute measurement of optical radiation parameters. For instance, the measurement of lamps that have different power ratings is only possible using array detectors that have a wide dynamic range. Precise, absolute measurements require the entire dynamic range of the spectroradiometer to be completely linearized and also require an accurate, traceable calibration. If the electronically controlled dynamic range (set by the integration time) is not sufficient, additional attenuating filters are needed. The filter selector must be mechanically robust to ensure long-term stability of the measurement system. For time-critical applications such as LED binning in pulsed mode, the electronically controlled dynamic range must be large enough to avoid the need for a time-consuming filter change during the measurement. For absolute measurements, an automated dark signal adjustment of the CCD is most beneficial. Spectroradiometers that are used for binning of front-end and back-end LEDs must accommodate precise synchronization of the measurement with the test LEDs operated in pulsed mode requiring suitable trigger interface and fast data readout.  Flash measurements, i.e. measurements within a light pulse, require an electronic shutter for instantaneous (ns) zero setting of all pixels before a measurement is triggered. The measurement of the luminous flux, luminous intensity, and luminous intensity distribution requires additional accessory components e.g., integrating spheres, luminous intensity lenses, and goniometers. Reproducible interfacing to these entrance optic accessories is essential. Direct mounting of the spectroradiometer onto the accessory equipment helps avoid influences of flexible light guide connections. Among the requirements of color measurements are precise calculations in accordance with CIE 13.3, CIE 15, and TM-30-15. For applications in the LED and semiconductor industries, the systems must also conform to the CIE S025 and LM-79-08 standards.

BTS2048-VL, diode array spectroradiometer with BiTec detector

The BTS2048-VL meets all the requirements of a high-end array spectroradiometer as well as being favourably priced despite its cutting-edge design.

One of its unique features is the innovative BiTec detector that consists of a V(lambda) filtered Si photodiode and a spectroradiometer unit based on a back-thinned CCD. This makes it extremely linear, stable, and fast. Both sensors can be used independently and the mutual correction of the sensors is advantageous for accuracy, speed and versatility (see article on BTS technology).

The fully linearized 2048 pixel CCD detector with an electronic shutter allows for integration times ranging between 2 µs and 4 s and offers an extremely broad dynamic range without the need for additional attenuating filters. This is three orders of magnitude more than the common millisecond integration times provided by lesser instruments.  An even wider dynamic range is provided by  the TEC-cooled spectroradiometer (BTS2048-VL-TEC).This variant has integration times ranging from 2 µs to 60 s. The 2 nm optical bandwidth ensures accurate spectral measurement values in the range between 280 nm and 1050 nm (0.4 nm/pixel).Mathematical bandwidth correction in accordance with CIE 214 has also been implemented for auto- correction of the measurement values. Si photodiodes exhibit exceptionally high linearity across their dynamic range. This makes them ideal for linearization of the CCD within the BiTec detector (see article on BTS technology). The constantly measuring diode can also be used to synchronize the measurement of PWM signals. This enables automatic recording of absolute spectral data using the BTS2048-VL, which is very difficult for conventional spectroradiometers without a BiTec sensor due to the integration time. In addition, the Si photodiode, which is fitted with a photometric filter (CIE V-lambda), can be used independent of the CCD. The device can therefore be used to perform fast measurements on very weak signals, something that makes the BTS2048-VL ideal for integration in goniometers and other systems. Another advantage of the BiTec technology in this context is the ability to integrate online correction of the spectral mismatch (f1’) of the diode using spectral data. Despite its compact dimensions of 103 mm x 107 mm x 52 mm (l x w x h), the BTS2048-VL spectroradiometer has a remote-controlled filter wheel with an OD1 and OD2 attenuation filter as well as a shutter for dark measurement.

 Applications in front-end and back-end LED binning

The BTS2048-VL is perfectly suited for industrial front-end and back-end LED binning applications. Its  back-thinned CCD based spectrometer, incorporates an electronic zero setting feature of all pixels before a measurement is triggered. The electronic shutter and triggering of the measurement can be synchronized with the power supply via a trigger port when the test LED is operated in pulsed current mode. The powerful microprocessor only requires 7 ms to transfer a complete dataset to the system computer via the fast LAN interface.

 Direct mounting instead of using a light guide

The BTS2048-VL spectroradiometer has a diffusor window and can therefore be used to measure the irradiance/illuminance, incl. spectrum, color, and color rendering index, without any accessory equipment. With the diffusor window, the BTS2048-VL can also be mounted directly onto accessories such as integrating spheres, luminance lenses (according to CIE 127), and goniometers in order to measure the luminous flux, luminous intensity, and luminous intensity distribution. Gigahertz-Optik also offers the BTS2048-VL-F for applications with light guides.

User software and developer software

The standard S-BTS2048 user software has a customizable user interface and is extremely easy to use. It has a large number of display and function modules which can be activated when configuring the BTS2048-VL with the respective accessories from Gigahertz-Optik GmbH.

The S-SDK-BTS2048 developer software is recommended for integration of the BTS2048-VL in the customer’s own software.


One essential quality feature of photometric devices is their precise and traceable calibration. The BTS2048-VL is calibrated by Gigahertz-Optik’s calibration laboratory that was accredited by DAkkS (D-K-15047-01-00) for the spectral responsivity and spectral irradiance according to ISO/IEC 17025. The calibration also included the corresponding accessory components. Every device is delivered with its respective calibration certificate.



Short description

High speed spectroradiometer with a wide dynamic range for CW and pulsed measurements of irradiance/illuminance, spectrum, luminous color, and color rendering index. Accessories for measurement of other parameters

Main features

Compact device. BiTec detector with back-thinned CCD (2048 pixels, 2 nm optical bandwidth, electronic shutter) and Si-photodiode with V(lambda) filter. Optical bandwidth correction (CIE214). Filter wheel with shutter and attenuation filters. Input lens with a diffusor window that has a cosine field of view. Automatic PWM synchronization

Measurement range

Spectral: 300 nm to 1050 nm, 1 lx to 3E8 lx (min. level by white LED with low saturation)

Integral: photometric 360 nm to 830 nm, 0.1 lx Noise signal up to 3E8 lx

typical applications

CCD spectroradiometer for design applications. Module for integration in test systems for front-end and back-end LED binning.


Factory calibration. Traceable to international calibration standards


Measured Quantity

Spectral irradiance (W/(m² nm)), irradiance (W/m²), illuminance (lx), spectral radiant intensity (W/(sr nm)), radiant Intensity (W/sr), luminous intensity (cd), dominant wavelength, peak wavelength, center wavelength, centroid wavelength, x, y, u´, v´, X,Y,Z, delta uv, color temperature, color rendering index (CRI) Ra, R1-R15, TM-30-15, CQS, CIE-170, etc.. Option integrating sphere: in addition spectral flux (W/nm) and luminous flux (lm) Option goniometer: in addition radiant intensity (W/sr) distribution and luminous intensity (cd) distribution


Accuracy class B according to DIN 5032 and CIE No. 69
Accuracy class A for f1`, u, f3 and f4 according to DIN 5032 and CIE No. 69

Input optics

Diffusor, cosine corrected field of view (f2 ≤ 3 %)

Filter wheel

4 positions (open, closed, OD1, OD2). Use for remote dark current measurement and dynamic range extension.


Parallel measurement with diode and array is possible, thereby linearity correction of the array through the diode and online correction of the spectral mismatch of the diode through a*(sz(λ)) respectively F*(sz(λ)).

Spectral Detector

Calibration uncertainty

Spectral irradiance

(300 – 304) nm:± 7 %
(305 – 349) nm:± 5 %
(350 – 399) nm:± 4.5 %
(400 – 780) nm:± 4 %
(781 – 1030) nm:± 4.5 %
(1031 – 1050) nm:± 5.5 %

Spectral irradiance responsivity (280 – 1050) nm. Standard calibration (350 – 1050) nm, optional recommended calibration (300 – 1050) nm. Full range possible for BTS2048-VL-TEC.

spectral range

(280 -1050) nm, see limitation for calibration

Optical Bandwidth

2 nm

Pixel resolution

~0.4 nm/Pixel

Number of pixels



Highly sensitive back-thinned CCD chip


16bit (25 ns instruction cycle time)

Peak wavelength

±0.2 nm

Dominant wavelength

±0.5 nm           *2

Δy Δx uncertainty

±0.0015 (Standard illuminant A)
±0.0020 (common LED)

Repeatability Δx and Δy



Standard illuminant A 30K; LED up to ± 1.5% depending of the LED spectrum

Band-pass correction

mathematical online band-pass correction is supported


completely linearized chip >99.6%

Stray Light

2E-4           *3

Base line noise

5 cts     *4


5000        *5

dynamic range

>9 Magnitudes

spectral irradiance responsivity range

(2E-5 – 2E5) W/(m²nm)           *6*7

CRI (color rendering index)

Ra and R1 to R15

typical measurement time

10lx    2,5s      *10
100lx    250ms      *10
1000lx    25ms      *10

Integration Time

2 μs – 4 s        *1

Integral Detector


Spectral responsivity with fine CIE photometric matching. Online correction of the photometric matching through spectral measurement data (spectral missmatch factor correction).

Measurement time

20 µs  – 6000 ms

rangerise time (10 – 90) %
0,1,250 µs
3,4,565 µs
6,7,81.5 ms
Measurement range

nine (9) measurement ranges with transcendent offset correction

Measurement range

min. measurable illuminance value (diode): 0.1 lx *11

max. measurable illuminance value(diode): 3E8 lx *12


Illuminance ± 2,2 %

f1′ (spectral mismatch)

≤6% (uncorrected)

≤1,5% (f1′ a*(sz(λ)) respectively F*(sz(λ)) corrected by spectral data, done automatically by BTS technology)


spectral responsivity

f2 (directional response/cosine error)



32bit for device control,16bit for CCD array control, 8bit for photodiode control


USB V2.0, Ethernet (LAN UDP protocol), RS232, RS485

Data transfer

Standard for 2048 float array values via ethernet 7ms, via USB 2.0 140 ms

Input Interfaces

2x (0 – 25) VDC, 1x optocoupler isolated 5 V / 5 mA

Output Interfaces

2x open collector, max. 25 V, max. 500 mA


Trigger input incorporated (different options, rising/falling edge, delayed, etc.)


User software S-BTS2048
Optional software development kit S-SDK-BTS2048 for user software set-ups based on .dll‘s in C, C++,C# or in LabView.

Power Supply

With power supply: DC Input 5V (±10 %) at 700 mA
With USB bus (500mA) *8


103 mm x 107 mm x 52 mm (Length x Width x Height)




Tripod and M6 screw threads

Front adapter UMPA-1.0-HL for use with integrating sphere port-frame UMPF-1.0-HL

temperature range

Storage: (-10 to 50) °C

Operation: (10 to 30) °C           *9


*1 It is recommended to perform a new dark signal measurement for every change in the integration time
*2 typical value, the uncertainty of the dominant wavelength depends on the spectral distribution of the LED
*3 typical value, measured 100nm left of the peak of a cold white broadband LED
*4 *5 typical value measured without averaging for a 4ms measurement time and full scale control of the array. Averaging results in quadratic rise of the S/N
i.e. quadratic fall of the base noise e.g. averaging to a factor 100 improves the S/N by a factor 10
*6 Minimum 500/1 S/N. Maximum at full scale control.
*7 Irradiation only allowed for a short time so as to avoid thermal damage
*8 during USB connection, not all functions are available due to the limited current supply e.g. no Ethernet
*9 Device requires for temperature stabilization approx. 25min. If a measurement is performed in the warm-up phase, or if measurements are performed under varying temperatures, dark signal measurement is required for each measurement. At high temperatures and at the maximum integration time a decreased dynamic can be used.
*10 measurement of a white LED and 20000 counts (signal-dark) saturation<
*11 Standard deviation of the noise in the most sensitive measuring range at 2s measuring time typical 1E-2 lx
*12 With OD2 filter, illumination only for very short time allowed due to thermal damage


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