The HLMP is always a "standard red" LED - not AlGaAs, "high efficiency", orange, or any other color chemistry. That's what is critical, the low efficiency (as a light source) gives it a low dynamic impedance. Originally they were made by HP, then by Agilent which was an HP spinoff, now it's somebody else - I don't know if they use the same equipment or not. The original HPs were also very quiet, probably due to excellent clean-room manufacturing. I've not done comparative evaluations of the currently available LEDs.
