How to position lighting and remove shadows in ros3djs?

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When I display markers using ros3djs they appear to be darker than they do on my default RViz setup. It seems my issue is related to lighting direction in ros3djs because I played around with different views in RViz and found that the same issues with shadowing there but from different directions. To me, it seems that I need to specify lighting direction in ros3djs. Is this possible?

Markers on ros3djs web GUI:

Markers on RViz:

I've played around with options like alpha and intensity in ROS3D.Viewer but these do not solve the problem. I'm hoping something like the pseudo code below might be available but I can't find anything on the docs here...... any ideas?

Initial viewer setup (real code):

let viewer = new ROS3D.Viewer({
    divID : 'map',
    width : 600,
    height : 600,
    background : '#FFFFFF',
    alpha : 1.0,
    antialias : true,
    intensity : 1.0,
    cameraPose : {x : -1, y : 0, z : 20},
    displayPanAndZoomFrame : true
});

Some pseudo code that I hope someone can advise how to properly implement:

viewer.addObject(new ROS3D.LightingPosition({x : -1, y : 0, z : 20}));