The description states PC with aluminum coating… I can only postulate that the center is not coated; helping to effect the large beam angle. And it’s a HUGE angle…
Could be either a clear or matte dome… or a fresnel + reflector setup, that’s where I’d bet my money.
With the central dome being hollow, it can’t be (single-surface) refraction towards the reflector.
RXI is just fine with PC. It’s all about folding optical path. Light goes up and is reflected (by TIR or metalization) down towards the bottom and towards the sides. Then the main reflector directs it forwards.
Refraction as the light enters and leaves the lens is usually used as well.
BTW every time I see that flat 50 mm optics I can’t help by wonder:
BLF Q8 has 4 domed XP-L.
XHP70 has 4 XP-L dies under a single dome.
How would the beam of Q8 compare to XHP70 under a flat optics?
Similar LED config.
Similar size, most XHP70 lights tend to have long heads but this one wouldn’t. Actually it would be shorter.
The flowery spill wouldn’t be there.
Those flat lenses don’t tend to be as narrow as possible. Would they have a donut hole?
Assuming a lens is wide enough to eliminate the donut - what would throw better? Q8 loses some frontal area due to being a quad. Lens needs to compensate for the donut.
Very low height due to fresnelized TIR. And packaging efficiency is very good. A 7-up would have about 40 mm diameter. 19-up would be about 66 mm.
Too bad there are no throwier versions. It significantly reduces the benefit of packing them tight.