clearskycalculator.com

What It Is

Clear Sky Calculator is an online clear-sky radiation calculator provided by Apogee Instruments Inc. It is used to estimate irradiance on a horizontal plane for any location and time worldwide. Its primary use case is comparing a radiation sensor’s measured PPFD against the model estimate to determine whether recalibration may be needed. The page explicitly recommends using it under clear, unpolluted, summer conditions and close to solar noon for better accuracy.

Core Features and Technical Details

The tool supports inputs such as location, date, time, time zone, latitude/longitude, elevation, air temperature, and relative humidity. It can also auto-fill some parameters via “Calculate Model.” Outputs include Model Estimated PPFD, Measured PPFD, and Difference from Model, and it prompts users to contact Apogee for recalibration when the difference exceeds the threshold for the selected sensor. The calculation notes state that clear-sky global shortwave irradiance is based on Appendix D of the ASCE Standardized Reference Evapotranspiration Equation, while UV-A, PAR, and ePAR are converted from shortwave irradiance using reference solar spectrum ratios.

From a developer-tool perspective, the currently captured content does not show API, SDK, CLI, batch calculation, webhook, or embeddable component capabilities, nor does it mention supported programming languages or frameworks. As such, it is better understood as a specialized web calculator rather than a developer integration platform. Open-source or closed-source licensing and self-hosting options are also not disclosed.

Pricing, Documentation, and Ecosystem

The page does not provide information about pricing, accounts, subscriptions, or payment methods, so its business model cannot be determined. The documentation is relatively strong: it includes usage steps, input/output definitions, explanations of intermediate variables, and descriptions of parameters such as solar constant, PAR/Solar, solar zenith angle, air pressure, vapor pressure, and shortwave irradiance. In terms of ecosystem, the only visible connection is to Apogee sensor recalibration services; no third-party integrations are apparent.

Pros, Cons, and Best-Fit Users

Its strengths are a clearly defined use case, transparent parameters, and documented model sources. It is suitable for radiation sensor users, agricultural light measurement professionals, environmental monitoring teams, and researchers who need an on-site calibration reference. Its limitations are strict usage conditions and sensitivity to weather, season, and solar elevation. It also lacks developer interfaces, open-source information, and deployment options, making it unsuitable for teams that require systematic integration or large-scale automated calculations.

Access from China

The captured text does not provide information about access from mainland China, network stability, or payment methods, so this remains unknown. For alternatives, users may consider NOAA, NREL/PVWatts, or open-source solar irradiance modeling libraries.