BTS256-EF - mobile light meter for photopic and scotopic illuminance, EVE factor, luminous color, color rendering index, luminous spectrum and flicker.
The BTS256-EF is a high-quality light meter that is well suited for illuminance and luminous color measurements in all application areas thanks to its compact design, high-quality light sensor and precise cosine field of view function. Another special feature of the device is its ability to perform flicker measurements.
BTS256-EF - mobile light meter for photopic and scotopic illuminance, EVE factor, luminous color, color rendering index, luminous spectrum and flicker
The BTS256-EF is a high-quality light meter that is well suited for illuminance and luminous color measurements in all application areas thanks to its compact design, high-quality light sensor and precise cosine field of view function.
BiTec light sensor for precise light measurements
One of the outstanding properties of this mobile light meter is its BiTec light sensor. This combines the characteristic properties of a silicon photodiode with those of a low-noise CMOS diode array. The BiTec sensor guarantees precise photometric and spectral-radiometric measurement values over a large dynamic range through mutual correction of the measurement signals of both sensors.
Silicon photodiode detector, fast and linear
When taking into account the dynamic range, linearity and speed, silicon photodiodes have always been and are still the ultimate light detectors. A photometric corrected silicon photodiode is therefore incorporated in the BiTec light sensor of the BTS256-EF light meter. Its matching to the photometric V(λ) responsivity is improved by the diode array’s spectral measurement data.
Diode array detector for spectral measurement data
The CMOS diode array of the BiTec Light sensor provides precise measurement data required for the luminous spectrum. This data is then used for calculation of the color values and scotopic illuminance as well as for optimization of the photometric responsivity.
Optimized Signal to Noise Ratio
The noise signal from diode array detectors has significant effect on the signal to noise ratio (SNR) and hence on the quality of the measurement signal as well. A remote controlled shutter in the BiTec light sensor enables online compensation of the dark signals that are dependent on the temperature and integration time.
Pulse Width Modulated (PWM) LED lamps
The fast photodiode of the BiTec light sensor enables the BTS256-EF to automatically synchronize itself to the frequency of lamps operated in PWM mode.
Precise cosine corrected field of view
A cosine corrected field of view is absolutely necessary for illuminance measurement devices. For extended illuminance setups, the cosine matching has significant influence on the measurement uncertainty of the light meter. The BTS256-EF light meter is equipped with a diffuser window with a 20mm diameter whose cosine matching ensures an f2 ≤ 3% uncertainty which corresponds to the DIN 5036 requirements for the quality class B. Both detectors of the BiTec light sensor are centrally aligned behind the diffuser window and therefore have the same view angle.
DIN quality class A and B luxmeter
Through the cutting-edge Bi-Technology sensor concept, use of modern electronics, online dark signal adjustment and the possibility to perform temperature compensation, the device meets the conditions specified for two of the DIN 5036 quality classes.
- In terms of the f2 uncertainty i.e. ≤ 3%, the device corresponds to the quality class B (DIN 5032 section 7).
- In applications where limitation of the viewing angle is acceptable, the BTS256-EF, with its f1’, u, f3 and f4 values, corresponds to the quality class A (DIN 5032 section 7).
Diverse photometric and colorimetric measurands
A much broader diversity of measurands as the one offered by conventional light meters is required for verification and testing of LED lamps. The BTS256-EF offers fourteen measurands and thereby meets all the requirements for a modern light meter:
- Ep photopic illuminance
- Es scotopic illuminance
- Es/Ep ratio of night and daylight vision
- EVE “Equivalent Visual Efficiency” factor
- Ee irradiance
- Eλ spectral irradiance
- x, y CIE 1931 color coordinates
- u‘, v‘ CIE 1976 color coordinates
- CT color temperature
- Δuv Deviation from the blackbody locus
- λdom dominant wavelength
- λp peak intensity wavelength
- λ0,5 spectral half-width
- Purity color purity
- CRI Ra and R1 to R15 Color Rendering Index
Non-visual response measurands
In addition to conventional rods and cones, the retina has melanopsin-containing photosensitive ganglion cells. Vision scientists have demonstrated unequivocally that melanopic light reception affects brightness perception and that the conventional photopic measurements require a correction to maintain a proper correlation with perceived brightness. In cooperation with the researchers who originally determined this correlation factor, Gigahertz-Optik now includes this Melanopic/Photopic and Brightness Perception function in the BTS256-E series meters.
The BTS256-EF displays:
- E (Melanopic / Photopic) display title
- Ep – This is Photopic Illuminance (lx)
- Em / Ep – This is Melanopic Irradiance (mW/m2) / Photopic Illuminance (lx) = mW/lm
- Em’ / Ep – This is Melanopic Illuminance (lx) / Photopic Illuminance (lx) = unit-less ratio
- B0.32 – This is Brightness Perception (lx) – other user defined constants may be input through menu setting
Display modes for standard measurements
The BTS256-EF Bi-Tec sensor luxmeter has several display modes where the necessary measurands for the common photometric measurements are incorporated. The cursor buttons can be used to switch between the displays.
Customized display modes
The BTS256-EF enables users to individually configure and save display modes. The required measurands can hereby be selected.
Info display for measurement parameters
An incorporated Info Display shows all the relevant measurement parameters.
Easy operation and handling
Three control buttons and the diligently structured menu navigation make the device easy and safe to operate the device. For instance, in the standard measurement mode, the user does not have to manually set the measurement parameters since these are automatically and best adjusted to match the measurement conditions. In the expert mode, the user has access to all measurement parameters.
Many useful extra functions
- If the user wants to distance himself from the device’s field of view, he/she can set a time-delayed measurement.
- The display can automatically be dimmed during the measurement.
- An acoustic signal can be set to mark the end of a measurement.
- A layout created using a PC with the support points for the single measurements can be adopted in the device for measurement of the illuminance distribution. The measurement points can be progressively processed and saved.
- Fast data logger measurement mode where time-clocked readings of the photodiode can be recorded at a maximum measurement rate of up to 100ms.
- A second data logger measurement mode that enables time-clocked recording of all measurands including the spectral measurement data.
- Date and time in real-time can also be set.
The measurement device has a tripod stand socket on the bottom side.
Protective cap with chain
The protective cap for the diffuser window is attached onto the device.
With this option the device can be controlled by the S-BTS256 per WiFi.
Use without PC
The BTS256-EF has all the necessary functions enabling free operation of the device without having to depend on a computer. Furthermore, the rechargeable batteries have a capacity of more than 8 operation hours. The USB power adapter enables recharging of the device without a PC.
Use with PC
The BTS256-EF additionally has a USB 2.0 interface for use with a PC. This enables both data exchange and battery charging.
The S-BTS256 software included in the device’s price provides all the necessary functions for the measurements, measurement data display and data transfer. The cutting-edge, flexible desktop concept of the software offers the user an individual constellation of the required measurement values. This can be a full screen filled with lux measurement values or a matrix with both numerical and graphical fields. Each desktop constellation can easily be saved for future use.
Software Development Kit
Gigahertz-Optik offers programmers the S-SDK-BTS256 Software Development Tool. This can be used with LabView from National Instruments, .NET from Microsoft and C/C++. The SDKs simplify integration of the BTS256-E in an internally developed software.
Compact, splashproof light meter with flicker measurement function for mobile use
Standard display showing the signal progression and signal frequency
Standard display showing the illuminance and flicker parameters
Standard display showing frequency components determined through Fast Fourier Transformation
Light meter with precise cosine field of view function
Display showing the scotopic and photopic illuminance and the S/P ratio as per IES TM-24-13
The measurement parameters protocol is saved together with a measurement data file
S-BTS256 user software with modular setup desktop
The graphical display module can be zoomed to full screen
|Range of measurement|
class B DIN 5032 part 7 or AA according to JIS C 1609-1:2006
Bi-Technology sensor with a photometric broadband detector and a array spectrometer. Integrated aperture for automatic dark signal adjustment.
Diffuser window with 20mm diameter, cosine corrected field of view, f2 Error ≤ 3%
Spectral responsivity with fine CIE photometric matching. Online correction of the photometric matching through spectral measurement data (spectral missmatch factor correction)
(380 - 750) nm
(5.2 - 30000) ms
Automatic aperture for dark signal measurements with the same integration time as that of light measurements. Aperture delay = 100ms.
|Typ. Measurement Time||
199,999 lx ≤ 5ms (white light)
100 lx ≤ 1s (white light)
|Color measurement range spectral||
(1- 199,999) lx
Scotopic measurement range spectral (1 - 199,999) lx
|Δx, Δy reproducibility||
+/- 0.0001 (Standard illuminant type A)
+/- 0.0002 (LED)
|Δx, Δy uncertainty||
+/- 0.002 (Standard illuminant type A)
+/- 0.005 (typ. LED)
|CCT Measurement range||
(1700 - 17000) K
+/- 50K (standard illuminant type A)
+/- 4% (depending on the LED spectrum)
|CRI (color rendering index)||
Ra and R1 to R15
6E-4 (Blue LED)
6E-4 (Green LED)
6E-4 (Red LED)
1E-3 (White LED)
≤3% (f1' a*(sz(λ)) respectively F*(sz(λ)) corrected)
|Max. measurable illuminance||
|Noise equivalent illuminance||
(0.1 - 6000) ms
|spectral irradiance sensitivity|
16Bit, 25ns instruction cycle time
5VDC, 450mA per USB
USB 2.0 (Type B USB)
Option WiFi: WiFi 2,4 GHz (external antenna, range > 100m)
Operation: -10°C bis +30°C
Storage: -10°C bis +50°C
333mm x 280mm x 70mm, 650g
159mm x 85mm x 45mm (Length x Width x Height)
|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|
|S-BTS256||Application software for BTS256 variants|