As you have explored this world extensively, you will know that there are some viewing posts that have the same coloured bulbs on top. If the below instructions don't work for you, maybe you have directed the beam incorrectly.
Ok, the light first shines through the yellow post. Then it needs to go to the blue post nearby, then to the green post far on the other side. Then to the nearby red (orangey) post, then to the closer yellow post (not the first one). Then to the purple post, then to the red post near where you first appeared and finally, up to the device in front of the tusk door.