And that's the key...
Diffusion...
Point source - Compared to other light sources LED,s are a lot like the old 3-D cell Magnum flashlight - Mirror and Lens system turns the flashlight into a spot light. Only Magnums ability has an adjustable focus/lens to turn it into a beam and back to flood - but still focused in one direction...
We use a 5mm LED with a flat front for this. The bullet-nose LEDs direct the light in a narrow cone.
Frosted lens also works but in any case, the epoxy molded "bullet" nosed are too focused to work well for the type of mount the HR2510 is. Has to be sanded, roughed up and somehow the "magnifier nose" needs to be sanded off to provide a more diffused light to light the chamber.
I've even seen "jumbo" LEDs wrapped with a 3M Scotch Tape (frosted/Satin hide type) as one type of method used to diffuse the light from a center cone to a more broadened globe - that was a mess to clear out...
The problem lies in how the point source the Grain of Wheat is, the light emanation was 360 degrees barring mount and shadows. LED uses that Gosh Darn Cup as the Cathode and the wire bonds to the grain for the Anode, between the two - that cup then takes the grains' light and shows (shoves) it into one direction - up - and the molded epoxy resin does the rest.
LED's come in various lens shapes, even colors, but all have the same inherited problem of mount design.
The Cup it's the only one that has proven to be rigid and strong/durable enough to handle the torques of everyday life.
The chip used isn't big enough to offset the height of the cusp of the cup - so that has been (it's) the shade of this design all along.