cube - shaped , ventilated , individual light modules housing a lamp or bulb having different predetermined characteristics are interchangeably mounted on an expandable clip surrounding an electrical socket , by sliding the module down on the clip and simultaneously establishing electrical contact between the bulb in the module and a power source and switch . the front of the module is faced with safety glass to protect the bulb and subject , and a space is provided between the module and protective safety glass which can be fitted with one or more , swing - away , wide angle adapter , diffuser , or dichroic lenses .