A discussion on some assemblies of Fresnel lens and quartz lamps in simulating quasi-parallel light for testing building models in heliodon studies

Abstract

Since the first heliodon developed in UK in 1930s, heliodons have been used to study and test the solar performance of physical building models by simulating direct sunlight to impinge onto building models, for various desirable combinations of latitude, day, and time of a day. [1, Fig. 1] In this first heliodon, a tungsten lamp was moved and fixed along a day selector scale to simulate the solar position. Light coming from this tungsten lamp subsequently impinging onto the building model differs from the real direct sunlight which is practically parallel, causing dimensional errors of the shadows of the components of the building models. To reduce these dimensional errors, the lamp and the lamp holder have to be placed further away. However, the further away the lamp from the building model, the weaker the light falling onto the building model which is not desirable. Fresnel lens is an integrated assembly of complex lens, a device invented about 100 years ago to redirect light coming from a point source into practically parallel light for projecting away to be visible at long distances, for equipping light houses at sea shores and harbour entrances. 100 years ago Fresnel lens was made of glass. Now Fresnel lens is commonly made of plastics of suitable grade. This paper discusses a few assemblies of Fresnel lens and quartz lamps for producing quasi-parallel light. i.e. practically parallel light, mimicking the practically parallel aspect on direct sunlight, for testing building models in heliodon studies. The assemblies should also produce reasonably strong light falling onto the building models, to minimize dimensional errors of the shadows of the components of the building models, to minimize space of operation and storage, to operate on the largest possible size of models, and to be mobile for the convenience of matching use with various types of heliodon assemblies which may be fixed type or mobile type, and which may demand building models to be stationary or rotating in the model testing processes.