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Phone: +1-978-462-1818


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This Product is discontinued, please refer to the Alternatives shown below under Similar Products or contact us directly.

Alternative Products for this discontinued product:

High Accuracy Flicker Meter and General Lighting Spectral Luxmeter


Hand-held portable PAR meter for quantum measurement of the Photosynthetically Active Radiation in horticultural applications

  • Advanced PAR light meter measures LED based and traditional natural or artificial horticultural (grow) lighting
  • Splash-proof housing PAR light meter & datalogger – ideal for greenhouse use
  • Measures PAR, PPFD, R/FR (Red/Far Red Ratio), DLI (Daylight integral)
  • Up to five user defined spectral weighting functions can be applied
  • Expanded LED color and light meter functions including  photopic and scotopic illuminance, spectral irradiance, CCT, CRI, color coordinates and more
  • WiFi version available for remote installations

Advanced features and functions along with hand-held portability enable on site or lab level measurement and datalogging of PAR, PPFD, R/FR, DLI in plant growth, soil science, horticulture and aquiculture applications.

The BTS256-PAR meter also serves as a high quality light, color and spectral meter. A full listing of its light and LED measurement quantities is shown below.

One unique feature of the BTS256-PAR meter is its BiTec Sensor for increased accuracy when measuring LED based or any other artificial or natural light source.

Gigahertz-Optik’s BiTec Sensor technology combines the wide dynamic range, unsurpassed linearity and fast response times of a silicon photodiode with those of a low-noise CMOS diode array. The BiTec sensor guarantees accurate PAR, photometric and spectroradiometric measurement values over a large dynamic range through mutual correction of the measurement signals of both sensors. Please see also our technical article about PAR measurements and the PAR implementation in PAR Meters.

Silicon Photodiode Detector, Fast and Linear

The silicon photodiode is equipped with a photopic filter with further improvement of its spectral match to the photometric V(λ) response by the diode array’s spectral measurement data in real time. The end result is much more complete, accurate absolute PAR, light, color and spectral measurement of   LED based and other grow lights to investigate the effect of spectral tuning in the horticultural world.

User Specific Weigthing Functions for individualized PAR Measurements

Up to five user experimental spectral weighting functions can be self-programmed into the PAR meter using the supplied S-BTS256 software and are saved in the PAR meter memory for continued use. This allows individual photosynthetic photon flux of different horticultural species to be analyzed.

Diode Array Detector for Spectral Measurement Data

The CMOS diode array part of the PAR meter BiTec Sensor provides precise spectral measurement data from 360 nm to 830 nm. 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 

Dark signals in diode array detectors negatively impacts the signal to noise ratio (SNR) and hence the quality of the measurement if they are not substracted precisely. A remote controlled shutter in all BiTec Sensor meters enables online compensation of the dark noise signals that are dependent on the temperature and integration time. 

Pulse Width Modulated (PWM) LED lamps

The BiTec Sensor’s fast photodiode enables the BTS256-PAR meter to automatically synchronize itself to the frequency of LEDs and lamps operated in PWM mode. This is especially important for LED grow lights or other LED PAR light sources.

Precise Cosine Corrected Field of View

A cosine corrected field of view is absolutely necessary for accurate illuminance measurement devices. For extended source illuminance setups, the detector cosine match has significant influence on the measurement uncertainty of the PAR light meter. The BTS256-PAR light meter is equipped with a 20 mm diameter diffuser window whose cosine match ensures an f2 ≤ 3% uncertainty corresponding to DIN 5036 quality class B requirements. Both BiTec Sensor detectors are centrally aligned behind the diffuser window sharing the same view angle.

DIN Quality class A for some Applications

In applications where limitation of the viewing angle is acceptable, the BTS256-PAR meter f1’, u, f3 and f4 values correspond to DIN quality class A (DIN 5032 section 7).

Diverse Photometric and Colorimetric Measurands 

A much broader diversity of measurands compared to other conventional PAR light meters, especially LED PAR meters, is required for verification and testing of LED based sources. The BTS256-PAR meter offers fourteen measurands for state of the art PAR, light and color qualification:

  • Ep photopic illuminance
  • Es scotopic illuminance
  • DLI (Daily Light Integral )
  • R/FR Red to Far-Red relationship
  • Qsy' PAR value PAR PPFD in µmol/(m²s) (photosynthetic photon flux density)
  • Esy1, Esy2, Etp1, Etp2 in W/m²
  • UWF User Weighting Function (input up to 5 different user spectral functions)
  • 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

Selectable Display Modes for Standard Measurements

The BTS256-PAR Bi-Tec Sensor PAR light meter provides several display modes where the necessary measurands for common photometric measurements are shown. Cursor buttons are used to switch between the displays. Users can individually configure and save display modes with user selectable measurands.

Info Display for Measurement Parameters

An incorporated Info Display shows all the relevant measurement parameters.

Easy Operation and Handling

Three front panel control buttons and logically structured menu navigation make the BTS256-PAR meter easy to operate. For instance, in the standard measurement mode, the user does not have to manually set the measurement parameters since these are automatically selected and adjusted to match the measurement conditions. In expert mode, the user has access to all measurement parameters.

Many Useful Extra Functions

  • Time-delayed measurement allows user to remove himself during exposure
  • Automatic dimming of the meter display during measurement.
  • Acoustic signal can be set to mark the end of a measurement.
  • A layout plan showing the single values at various measurement points can be setup using PC/software to map 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.
  • Tripod mount socket
  • Protective diffuser cover with lanyard

Tripod mount and Wi-Fi Option

The measurement device has a tripod stand socket on the bottom side. With that help it can be easily placed in a greenhouse, etc. Wi-Fi option, splash proof design and (2) data logger functions enable the BTS256-PAR meter to be deployed remotely like in a greenhouse. (>100 m if visual contact to PC is guaranteed)


Direct Use or Remote Options:

  • Without PC: The BTS256-PAR meter has all the necessary internal functions and on board display for stand-alone use. Rechargeable batteries have >8 hour capacity. The supplied USB power adapter recharges the meter without a PC.
  • Use with PC: The BTS256-PAR meter is equipped with USB 2.0 interface. USB is used for both data exchange and battery recharging.
  • User software: Supplied S-BTS256 software provides all the necessary functions for the measurement, data display and data transfer. The cutting-edge, flexible desktop concept of the software offers the user individual configuration of the required measurement values. This can be a full screen filled with only lux measurement values or a matrix with both numerical and graphical fields. Each desktop constellation can easily be saved for future user
  • Software Development Kit: Gigahertz-Optik offers programmers the optional S-SDK-BTS256 Software Development Kit. The SDK can be used with LabView from National Instruments, .NET from Microsoft and C/C++, Python and others. The SDKs simplify integration of the BTS256-PAR meter into internally developed software.

For further information see our technical article on PAR measurement, implementation and PAR meters

Note: The BTS256-PAR has been integrated into the BTS256-EF which now includes all functions. When ordering this device you will also be able to perform flicker evaluations.


Light meter with a precise cosine field of view function

Light meter with a precise cosine field of view function

R/FR ratio

R/FR ratio

DLI measurement

DLI measurement

Standard display for the illuminance and spectrum

Standard display for the illuminance and spectrum

Ratio of the scotopic and photopic illuminance with the EVE factor as per IES TM-24-13

Ratio of the scotopic and photopic illuminance with the EVE factor as per IES TM-24-13

The measurement parameters protocol is saved together with a measurement data file

The measurement parameters protocol is saved together with a measurement data file

Standard display with illuminance, x,y color coordinates, color temperature and emission spectrum of an energy saving lamp

Standard display with illuminance, x,y color coordinates, color temperature and emission spectrum of an energy saving lamp

S-BTS256 user software with modular setup desktop

S-BTS256 user software with modular setup desktop

The graphical display module can be zoomed

The graphical display module can be zoomed

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