Abstract: A device and method permits detecting, measuring, and recording the intensity of radiation corresponding to a green plant's photoactive spectrum striking a selected site, and utilizing such information alphanumerically and graphically displaying the photoactive radiation exposure in sols incident at the site during a particular portion of a day, an entire day, a week, or an month. The photoactive radiation information provided by the invention device allows gardeners, farmers, researchers and others to match the types of trees, shrubs, crops or other plants that would grow best under the radiation conditions usually incident at the site over a desired, extended time period.