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The BTS256-LED light meter

The compact BTS256-LED meter is designed to measure the luminous flux, spectrum, color, and color rendering index of LEDs. One of its key features is the conical measurement port at the entry of the integrating sphere for measurement of individual onboard LEDs. The conical adapter is attached using a bayonet connector which makes it possible to use the BTS256-LED with other entrance optic options. Gigahertz-Optik also offers different accessories as part of the BTS256-LED Plus Concept with which the capabilities of the BTS256-LED can be enhanced.

Enhancement of the BTS256-LED using the diffusor window

The addition of the BTS256-LED-DA diffusor window to the BTS256-LED makes it possible to use the device for illuminance measurements. It provides the required cosine correction over a +/- 30o degree field of view and is therefore only recommended for measurement of directional lamps. Illuminance measurement of extended lighting systems and street lights should be performed using Gigahertz-Optik’s MSC15 and BTS256-EF.

The BTS256-LED-DA diffusor window is also necessary when the BTS256-LED is to be combined with the GB-GD-360-R40-2 goniometer to measure the luminous intensity radiance distribution.


One essential quality feature of photometric devices is their precise and traceable calibration. The BTS256-LED-DA with BTS256-LED 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 with the BTS256-LED-DA diffusor window for illuminance measurements.
1) BTS256-LED & BTS256.LED-DA 2) Integrating sphere 3) Precision bayonet mount with diffus window 4) BiTec sensor with Si photodiode, CMOS diode array spectrometer and shutter 5) Microprocessor 6) USB 2.0 interface 7) Light incident 8) Conical measurement port with precision bayonet mount
BTS256-LED with the BTS256-LED-DA diffusor window for measurement of the luminous intensity radiance distribution using the GB-GD-360-R40-2 goniometer.
Full screen display of the luminous spectrum
S-BTS256 user software with modular desktop setup
CIE 1976 chromaticity table with binning fields
CRI Bar Plot
Short description

Function enhancement to allow for illuminance measurements

Main features

Cosine diffusor with bayonet connector for use with the BTS256-LED spectroradiometer

Measurement range

40 lx to 400000 lx (spectral), 0,2 lx to 250000 lx (integral), 360 nm to 830 nm

typical applications

Enhancement of the BTS256-LED functions to allow for illuminance measurement of spot lamps as well as use with the GB-GD-360-R40-2 goniometer


Factory calibration. Traceable to international calibration standards

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.

Calibration uncertainty

Illuminance ± 2.2 %

spectral irradiance

(360 – 399) nm


(400 – 830) nm



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

Spectral Detector
max. illuminance

400,000 lx

min. illuminance

40 lx

Integral Detector
max. illuminance

250000 lx

Noise equivalent illuminance

0.2 lx

Type Description File-Type Download
Datasheet BTS256-LED-DA PDF
Produktname Product Image Description Show product
GB-GD-360-RB40 Goniometer for the measurement of 2π sources.

Features: Measurement of the luminous and radiant intensity distribution as well as luminous flux and radiant power from compact spot lamps and light-emitting diodes. Measurement distance 100 mm to 2000 mm. Remote control. Optional Lightmeters, user software, etc.
S-SDK-BTS256 Software Development Kit for BTS256 variants.
Article-Nr Modell Description Request / Compare
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 the BTS256-LED-DA adapter for the illuminance [lx] and spectral responsivity

15298218 S-SDK-BTS256

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

Further Information

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