This wide spectrum digital meter measures solar radiant energy intensity directly transmitted through glass (or the film-glass combination) in units of BTUs per square foot per hour or watts per square foot. Effective tool showing the relative effectiveness of various films in blocking solar radiant heat. Especially useful for showing how a very dark dyed film may allow far more energy to pass through than a much lighter metallic film. Can also be used in metric units. Powered by a 9-volt alkaline battery (included).