BF5 Sunshine Sensor

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BF5 Sunshine SensorBF5 Sunshine SensorBF5 Sunshine Sensor in the fieldComputer Generated Shadow Mask


  • Measures global and diffuse radiation
  • Sunshine duration
  • No moving parts, no shade rings
  • PAR reference sensor for SunScan System
  • Outputs can be PAR (mmol.m-2.s-1), Energy (W.m-2) or Lux

The BF5 Sunshine Sensor is a versatile, multi-purpose solar radiation sensor. It uses an array of photodiodes with a unique computer-generated shading pattern to measure incident solar radiation. A microprocessor calculates the global and diffuse components of the radiation and determines the sunshine state.

Two analogue voltage outputs give global and diffuse radiation, from which direct and diffuse radiation are derived. The sunshine state is indicated by a digital output. The three outputs can be connected to appropriate channels on the GP1 or GP2 data loggers, or other loggers commonly used for environmental monitoring. An internal heater keeps the BF5 Sunshine Sensor clear of dew, ice and snow down to -20 °C.

Sunshine Duration

The BF5 Sunshine Sensor measures sunshine hours indirectly using a simple equation based on the total PAR radiation (Photosynthetically Active Radiation), and the ratio of total to direct PAR. This sunshine algorithm corresponds closely to the World Met Office threshold of 120 W/m-2 in the solar beam for sunshine duration. The BF5 Sunshine Sensor does not need to be adjusted or repositioned to track the sun – a distinct advantage over devices with shadow rings. There are no complex electro-mechanical assemblies and no burnt paper tracks to interpret.

SunScan Canopy Analysis System

The BF5 Sunshine Sensor can be used as an integral component of the SunScan Canopy Analysis system. The SunScan Probe is a 1 m long light sensor array suitable for measuring PAR interception by plant canopies and estimating LAI (Leaf Area Index). The BF5 Sunshine Sensor improves the accuracy of the SunScan system and enables it to be used even under variable light conditions.


In addition to its role in the SunScan System, the BF5 Sunshine Sensor’s alternative outputs enable it to be used in the study of photosynthesis, illumination and solar energy measurement.

For building energy management systems (BEMS), the BF5 can be used to control the opening and closing of blinds or louvres in response to sunlight. The BF5’s ability to measure both the energy in the direct beam and also total radiation, makes it possible to optimise the use of natural light and solar gain while minimising glare for the building’s occupants.

Comparison with SPN1 Sunshine Pyranometer

The SPN1 Sunshine Pyranometer is a precision version of the BF5 Sunshine Sensor and although the two instruments have some features in common, there are important differences. These are summarised in the document: “SPN1 and BF5 Comparison Data Sheet”.


REFERENCES: Wood J, Muneer T, Kubie J (Feb 2003), “Evaluation of a new photodiode sensor for measuring global and diffuse irradiance, and sunshine duration” Journal Solar Energy Engineering.



For simultaneous outputs of total radiation, diffuse radiation and sunshine status. Output can be pre-set to PAR, Energy or Lux units.


Output setting
PAR Energy Illuminance
Units µmol.m-2.s-1 W.m-2 klux
Overall accuracy: Total ±10 µmol.m-2.s-1 ±12% ±5 W.m-2 ±12% ±0.600 klux ±12%
Overall accuracy: Diffuse ±10 µmol.m-2.s-1 ±15% ±20 W.m-2 ±15% ±0.600 klux ±15%
Resolution 0.6 µmol.m-2.s-1 0.3 W.m-2 0.060 klux
Range 0-2500 µmol.m-2.s-1 0-1250 W.m-2 0-200 klux
Analogue output sensitivity 1 mV = 1 µmol.m-2.s-1 1 mV = 0.5 W.m-2 1 mV = 0.100 klux
Analogue output range 0-2500 mV 0-2500 mV 0-2000 mV


Accuracy : Sunshine hours±10% compared to the WMO definition
Accuracy : Cosine correction±10% of incoming radiation over 0-90° Zenith angle
Accuracy : Azimuth angle± 5% over 360° rotation
Temperature coefficient± 0.15 % /°C (typical)
Temperature range-20 to + 50°C with Alkaline batteries
-20 to + 70°C with Lithium batteries
StabilityRecalibration recommended every 2 years.
Response time< 250 ms
Spectral response400-700 nm
Latitude capability-90° to + 90°
EnvironmentalIP65 ( shower and dust proof)
Sunshine status : contact closureNo sun = open circuit
Sun = short circuit to ground
Internal battery2 x 1.5 V AA alkaline batteries
Power requirement2 mA (awake ), <30 µA (asleep)
Heater power12 V – 15 VDC, up to 1.5 A
Battery lifetime1 year (typical)
Input voltage range – powered from internal battery1.4 to 3.6 VDC
Input voltage range – external power5 to 15 VDC
Fuse trip point, on sunshine status signal, (when in switch-closure mode)0.5 A, 30 V (self-resetting)
Max applied voltage to sunshine status output, in contact closure mode0 to 24 V
RS232 connector5-pin M12
Signal output & power-in connector8 pin M12
Mounting options:Camera tripod socket (¼ inch Whitworth). Holes for 4 x M4 bolts at corners of box.
Size & Weight120 mm x 122 mm x 95 mm, 635 g


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