In this chapter the various methods by which light from a source can be controlled are described and discussed. The challenge is to produce a design that is the cheapest possible, has the best possible light distribution, involves the least possible loss of light, is of pleasing appearance, and does not involve complicated manufacturing processes. Some of these requirements are nearly always conflicting, some — for example the best possible light distribution or good appearance -may be matters of opinion, but they do provide the questions the designer has to keep asking.