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Measurement of the luminous intensity distribution

Luminous intensity distribution is used to specify the directional radiation characteristics of lamps. It is determined by numerous separate measurements of the luminous intensity. Every measurement detects the light emitted into the half space around the lamp under a different viewing angle. The measurement data are represented in polar plots and 3D graphs and output in standard formats e.g., IES, EULUMDAT, Excel, etc. This data can also be used to calculate the luminous flux.

The BTS256-LED light meter

In its standalone mode, the compact BTS256-LED meter is designed for the convenient measurement of luminous flux, spectrum, color, and color rendering index of single LEDs. A key feature is the conical measurement port at the entry of the internal integrating sphere which enables the measurement of onboard LEDs. The bayonet connector used to attach the conical adapter makes it possible to combine the BTS256-LED with other accessory components. Gigahertz-Optik offers different accessories as part of the BTS256-LED Plus Concept which greatly extends the measurement capabilities of the BTS256-LED. These include the BTS256-LED-DA diffusor window which facilitates illuminance and luminous intensity measurements.

Enhancement of the BTS256-LED using the GB-GD-360-RB40-2 goniometer

The BTS256-LED-DA spectroradiometer can be combined with the GB-GD-360-RB40-2 goniometer in order to measure luminous intensity distributions. Unlike other diode array spectrometers that are available on the market, the BiTec sensor of the BTS256-LED offers the option to perform the measurement with just its photometric photodiode. Its short measurement times allow for measurements that are much faster than conventional spectrometers. In cases where spectrum, color, and color rendering index are also needed, the array-based spectrometer of the BiTec sensor may be employed. The GB-GD-360-RB40-2 goniometer allows for the alignment of the test lamp to the device with two degrees of freedom. The rotary movements are controlled remotely via stepper motor drives. The turntable has an M4 holes arrangement for universal attachment of the test lamps. Four mini-sockets provide four-terminal connection. The turntable enables fine tuning with 5 mm stroke and a coarse tuning with 100 mm stroke for alignment of test lamps in the goniometric axis. A removable stop is integrated to aid the alignment of the test lamp in the goniometric axis. The distance between the device and the test lamp can be varied between 100 mm and 2000 mm. The short distance is chosen for measurement of single LEDs with low intensity. The longer distance is better suited for measurement of extended LED arrays and LED lamps. The broad dynamic range of the GB-GD-360-RB40-2-BTS2048-VL makes it better suited for measurement of spot lamps that have a distinctive edge profile. The rail on the guide carriage is stiffened with a stable base. The BTS256-LED and BTS256-LED-DA can also be used without the goniometer.


The S-BTS256 user software supports operation of the goniometer and display of measurement values. It can be used to create measurement sequences as well as configure different settings. The measurement data can be exported to standard formats such as IES, EULUMDAT, ASCII, and Excel. Besides the display of the luminous intensity distribution in polar graphs and 3D plots, the software can also be used to calculate the luminous flux as well as display the spectrum, color values, etc.


One essential quality feature of photometric devices is their precise and traceable calibration. The BTS256-LED-DA is calibrated by Gigahertz-Optik’s calibration laboratory that is 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.

BTS256-LED spectroradiometer with the GB-GD-360-RB40-2 goniometer
Display of the luminous intensity distribution in a polar diagram
Display of the luminous intensity distribution in a 3D diagram
BTS256-LED for measurement of the luminous flux, spectrum, color, and color rendering index of single LEDs
The S-BTS256 user software supports measurement and display of the luminous intensity distribution curve in 2D and 3D.
Full screen display of the luminous spectrum
CIE 1976 chromaticity diagram with binning fields
Short description

Goniometer for measurement of the luminous intensity distribution of 2pi LED lamps. Wide dynamic range thanks to the variable measurement distance to the sample. Measurement of the luminous intensity, spectrum, color, and color Rendering index

Main features

Goniometer with a 360 mm distance between the optical axis and guide rail. Remote-control with a stepper motor drive. Measurement device with BiTec light sensor for fast measurements of the luminous intensity and spectral measurements of the spectrum, color, and color rendering index. Spectroradiometer that can be used without the goniometer.

Measurement range

40 cd to 400000 cd (spectral), 0.2 cd to 250000 cd (integral) at a measurement distance of one meter, 360 nm to 830 nm.

typical applications

Inspection of incoming products (LED lamps), quality assurance in production processes, design


Factory calibration. Traceable to international standards

typical applications

Light meter for the luminous flux, spectral radiant power, luminous intensity distribution and luminous color. Calculation of the luminous intensity from the illuminance and the measurement distance.

Calibration uncertainty

Luminous flux calibration ± 8%
Illuminance ± 4%


Bi-Technology sensor with a photometric broadband detector and a array spectrometer. Integrated aperture for automatic dark signal adjustment.

Goniometer Bench

Two-axes goniometer with step motor drive:

Phi-axis (horizontal) ±90°, 0.1° resolution, 0.2° reproducibility
Theta-axis (axial) ±18°, 0.2° resolution, 0.4° reproducibility

Sample holder:

160mm diameter with 25 mm threaded bores pattern
Four electrical terminals with terminal strip
Sample depth - max. 100 mm
Sample weight - max. 1kg

Optical bench:

2 m long guide rails on a 2.5 m long rack

Adjustable measurement device holder

Input optics

Bayonet adapter with diffuser window. 20 mm diameter of the diffuser window. ± 30° cosine corrected field of view. 5% cosine correction within the specified range.


This device is based on the BTS256-LED, please find detailed specification there.

Spectral Detector
typical measurement time

Max. luminous flux BTS256-LED: typ. 1100lm. Meas. time ≤ 5m
Min. luminous flux BTS256-LED: typ. 10mlm. Meas. time ≤ 30s

Max. illuminance BTS256-LED-DA: typ. 4000000lx. Meas. time ≤ 5ms
Min. illuminance BTS256-LED-DA: typ. 40lx. Meas. time ≤ 30s

Max. luminous intensity BTS256-LED-DA: typ. 4000000cd in 1m distance. Meas. time ≤ 5ms
Min. luminous intensity BTS256-LED-DA: typ. 40cd in 1m distance. Meas. time ≤ 30s


(Note: Measured by white light)

Optical Bandwidth

5 nm

spectral range

(360 - 830) nm

Integral Detector
Measurement range

Max. measurable luminous flux BTS256-LED: typ. 70000 lm

Noise equivalent luminous flux BTS256-LED: typ. 0.05 mlm

Max. measurable illuminance BTS256-LED-DA: typ. 250000 klx

Noise equivalent illuminance BTS256-LED-DA: typ. 0.2 lx

Max. measurable luminous intensity BTS256-LED-DA: typ. 250000 kcd in 1 m distance

Noise equivalent luminous intensity BTS256-LED-DA typ. 0.2 cd in 1 m distance

(Note: White Light)

Type Description File-Type Download
Datasheet GB-GD-360-RB40-2-BTS256-LED PDF
Dimensions GB-GD-360-RB40-2 PDF
Produktname Product Image Description Show product
S-SDK-BTS256 Software Development Kit for BTS256 variants.
Article-Nr Modell Description Request / Compare
15298602 GB-GD-360-RB40-2

Photometer bench with moveable detector holder. Measurement distance 100mm to  2000mm. Two axis goniometer GB-GD-360. RS485 to USB converter and power supply. 

15297922 GB-AD-300-100-LI

DUT alignment support tool. Case.

15308420 BTS256-LED

Measurement device, BTS256-LED-CA10 cone adapter, USB cable, hard-top casing, operation manual, software CD, calibration certificate.

15297959 BTS256-LED-DA

Diffuser window adapter with bayonet connector. Calibration of the illuminance (lx)

15300226 K-BTS256-LED-I

Recalibration of the BTS256-LED Tester. Only possible with the 10mm cone adapter

15300729 K-BTS256-LED-DA-I

Recalibration of the BTS256-LED Tester with BTS256-LED-DA adapter for illuminance [lx] and spectral responsivity

15298218 S-SDK-BTS256

Software Development Kit for the implementation of the BTS256 or variants into custom made software

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