In the object properties, you can **turn off** *Ray Visibility* of the 'emission object' for the camera:

![enter image description here][1]

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As of **Blender 2.76** the *Ray Visibility* panel was renamed to *Cycles Settings*:

[![enter image description here][2]][2]

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As of **Blender 2.8x**, *Ray Visibility* panel is now part of the new *Visibility Panel*:

[![enter image description here][3]][3]

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You can also run this script to *toggle* the *Camera Ray Visibility* for *selected objects* (updated for 2.8x):

    import bpy
    
    for obj in bpy.context.selected_objects:
    
        # toggle mesh lights
        if obj.type == 'MESH':
            for slot in obj.material_slots:
                if slot.material:
                    for node in slot.material.node_tree.nodes:
                        if node.type == "EMISSION":
                            obj.cycles_visibility.camera = not obj.cycles_visibility.camera
    
        # toggle light types
        if obj.type == 'LIGHT':
            obj.cycles_visibility.camera = not obj.cycles_visibility.camera


  [1]: https://i.sstatic.net/dXtKM.jpg
  [2]: https://i.sstatic.net/RvvsC.png
  [3]: https://i.sstatic.net/9nr7Y.jpg