In various cases, it might become handy to have lights that shine in preview only and do not affect de render result. This can be done easily, but requires the use of the Advanced interface to the Material Room. The options required are not available through the Simple interface.
Open de Light features in Material Room, and black out the Diffuse and Specular entries.
Note: under IDL (InDirect Lighting) rendering conditions, all objects in the scene behave as a light, but diffuse only (no highlights). IDL lighting does not show in preview. But IBL (image based, direct) lights do show in preview, producing the appropriate local colors as well. So, in order to approximate IDL conditions – like a sky dome – in preview: add an IBL with the same dome image, and have its Diffuse channel blacked out (to have it switched OFF at render time).
Do pay attention to the appropriate orientation of the image, though!