Calculates clear sky direct beam and diffuse sky solar spectral irradiances and the sum of these two spectra for sun positions and atmospheric conditions specified by the user. Sunspec version 1.0 also calculates the spectral irradiances incident on an arbitrarily tilted plane due to the direct beam, diffuse sky, and ground reflections. Sunspec integrates these spectra to determine the total irradiances, illuminances, and luminous efficacies for each component. Version 2.0 is in preparation and should be available by late-1997. Version 2.0 will be mouse-driven with user friendly I/O.

Sunspec offers the user a menu of typical atmospheric conditions to choose from and follows this with detailed editing screens permitting the user to change any input parameter. The input parameters include values for ozone concentration, water vapor, turbidity, ground reflectance (albedo), solar altitude and azimuth angles, and tilted plane altitude and azimuth angles. Sunspec includes a loop option permitting repeated calculations at different solar positions for the same atmospheric conditions. It also has an option for outputting solar spectral data files that can be read by the Window 4 program that calculates the solar optical and heat transfer properties of windows in buildings.


solar radiation, illuminance, irradiance, luminous efficacies, solar position



Expertise Required

Basic understanding of solar geometry.




Architects, building designers, fenestration energy performance simulators, atmospheric scientists, and others interested in determining the spectrum of radiation from the sun and sky.


User-friendly I/O screens, solar position, atmospheric conditions.


Results can be printed directly to a printer, or saved to a print file or to files formatted for importing into graphic plotting programs.

Computer Platform

DOS-based IBM and compatible personal computers; can also run under MS Windows.

Programming Language

Visual BASIC for DOS version 4.5


Provides a solar spectrum data file with columns for wavelength, direct normal, direct horizontal, direct tilted, diffuse horizontal, and diffuse tilted spectral irradiances, and the global (both direct and diffuse) versions of these. Also outputs the integrated total irradiances in W/m2 and the total integrated illuminances in lux for all these beams.


Current menu of typical atmospheric conditions is limited. Does not yet have the latest version of the SMARTS algorithm and is not as user-friendly as is planned for a future version.



Florida Solar Energy Center


1679 Clearlake Road
Cocoa, Florida 32922-5703
United States


(407) 638-1414


(407) 638-1439




Sunspec 1.0 is available from the contact at a cost of $35 (including shipping and handling).