Pyranometer vs Pyrheliometer vs Pyrgeometer vs Net Radiometer
These four instruments look similar but measure different parts of the radiation balance: total solar radiation, direct beam only, longwave infrared, or the net balance of incoming and outgoing radiation.
Pyranometer
A pyranometer measures total (global) solar radiation across a hemisphere, combining direct sunlight and diffuse sky radiation, typically over the 0.3-3 μm spectral range. The TBQ-2-B in this range uses a wire-wound electroplated thermopile under a double-layer quartz glass dome and outputs 0-50 mV or RS485. Pyranometers are the general-purpose choice for solar resource assessment and PV plant monitoring.
Pyrheliometer
A pyrheliometer measures direct beam solar radiation only, the radiation arriving in a straight line from the sun, excluding diffuse sky radiation. Because it isolates the direct beam, it needs to track the sun's position, which makes it a specialist instrument compared to a pyranometer. The TBS in this range shares similar sensing technology (thermopile, 0.3-3 μm range) but is built specifically for direct-beam measurement, used in solar concentrator research and detailed atmospheric studies.
Pyrgeometer
A pyrgeometer measures longwave (infrared) radiation, the thermal radiation emitted by the atmosphere and clouds rather than incoming sunlight, typically in the far infrared range. The ZDFD in this range uses a silicon arc light filter and thermopile sensing element with a 180° field of view. It's used for radiation balance studies where both incoming shortwave and outgoing longwave radiation need accounting for.
Net radiometer
A net radiometer combines upward- and downward-facing sensing domes on one instrument to measure net radiation, the balance between incoming and outgoing radiation at a surface. The ZNR in this range covers a wide 0.3-100 μm spectral range with dual quartz domes and needs no external power. It's the instrument of choice for soil evapotranspiration and surface energy balance calculations, where you need the net figure rather than any single radiation component.
Which instrument for which measurement
If you need general solar resource data for a PV site, a pyranometer covers it. If you specifically need the direct-beam component isolated from diffuse sky radiation, that requires a pyrheliometer with sun-tracking. If you're studying the atmosphere's own thermal radiation rather than solar input, that's a pyrgeometer. If your calculation needs the net balance of all incoming and outgoing radiation at a surface, for evapotranspiration or heat balance work, a net radiometer measures that directly rather than requiring you to combine readings from separate instruments.
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Frequently asked questions
What's the difference between a pyranometer and a pyrheliometer?+
A pyranometer measures total solar radiation across a hemisphere (direct plus diffuse). A pyrheliometer isolates only the direct beam from the sun and needs a sun-tracking mount to stay aimed at it, making it a more specialist, higher-maintenance instrument.
Do any of these radiometers need external power?+
No, all four instrument types in this range are self-powered thermopile sensors that generate their own voltage signal proportional to radiation intensity, outputting 0-50 mV (or RS485) without requiring an external power supply.
Which instrument do I need for evapotranspiration calculations?+
A net radiometer, since evapotranspiration calculations need the net radiation balance (incoming minus outgoing) at a surface, which a net radiometer measures directly with its paired upward and downward-facing sensing domes.