In ros3djs, what changes when the intensity option is varied?

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I'm using ros3djs for visualisation of markers, maps and laser points in a web browser. I define the viewer using the code below but do not see any difference when I add and vary the intensity option. What behaviour is expect with intensity set at various levels? I can't seem to notice any difference in lighting intensity whatever the value is set at. Any ideas what I might be doing wrong?

let viewer = new ROS3D.Viewer({
    divID : 'viewer',
    width : 1000,
    height : 600,
    antialias : true,
    intensity : 0.8,
    background : '#FFFFFF',
    displayPanAndZoomFrame : true,
    cameraPose : {x : -1, y : 0, z : 10}
});