Optical system
The first important issue to be considered in optical design is to study which of the three methods of reflection, refraction and diffusion is the most suitable, or to use a combination of the three.
A reflective system made of specular reflective material is superior to a refraction system because more luminous flux can be controlled using a simple optical system. It is particularly useful for lamps that require light to be focused into a beam (such as searchlights). In general, indoor lamps do not use specular reflective devices, except for some occasions that require particularly strict restrictions on glare.
When several beams are required from a light source, a prism or lens refraction system can be used, such as a lighthouse. Street lamps that require multiple beams but require the lamps to remain compact can also use this type of device. Polyhedral refraction plates (i.e. prism-type light controllers) can also be installed on general indoor fluorescent lamps. It does not control glare as strictly as Reflectors, but can obtain a higher light output ratio and has a better appearance.
Where light does not need to be strictly controlled, a translucent milky white diffuser can be used. The intensity of a lamp using a diffuser in any direction is roughly equal to the product of the projected area and the diffuser brightness, so some degree of light control can be achieved by changing the shape of the diffuser, even if the direction of maximum light intensity is required to have the largest projection area.
The last method of light control is shading. This can be achieved by using a matte white reflective surface to shading, which can reflect light in some directions and block light in other directions. This method cannot achieve a narrow beam, but glare control may be better. If strict glare control is required, black surface shading can also be used, but this will reduce the efficiency of the lamp.
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