He hung out with William Burroughs in Morocco, and built his machine in Paris (I think). It's a column of black poster board, on top of a turntable, with holes cut in the cardboard. Hang a lightbulb in the middle. Different levels have different amounts of holes, so you get a different strobe speed, depending on where you focus (with eyes closed). It's like a strobe, synchronized to Alpha brain frequency.
If you're interested I'll dig up the web reference.

Apparently he tried to pitch it to Columbia records, and told them someday music would be recorded with light!

Well, in addition to the possible benefits, it also presents a wide series of problems.

For example, most VR systems operate at 30 frames per second per eye. This particular rate, by the way, is what creates the "real" 3d effect. Anything lower and the eye is not so easily fooled.

Thus, if one were to attempt entrainment with existing tech, one would be limited to divisors of 30. Some VR systems can operate at other, faster rates, such at 60 fps / eye, in which case you're left with divisors of 60.

Unless someone starts desigining variable frame-rate VR goggles for brainwave entrainment purposes, then VR technologies will remain less than ideal for that purpose. Current tech is designed with ENTERTAINment in mind, not ENTRAINment. Basically, existing tech requires a total redesign from the ground up to be "useful" as an brainwave entrainment technology.

Someone will no doubt do this in the future, but realistically, I think we're looking at a requirement of frame rates that are MUCH higher than the current tech is capable of handling in order to achieve useful entrainment. Also, I don't think it will be neuroscientists leading the way with VR, and thus we'll probably have to wait until someone else invents goggles capable of such high frame rates before we actually see someone developing a VR entrainment technology.