Infrared Emitter Options with 940nm wavelength (sorted by price):

As shown in my "Choice of Infrared Wavelength" section, sunlight has very little 940nm radiation, so my preference is to use 940nm. To reach long distance, I want high peak current and radiant power, and a narrow beam angle is likely to help too. Due to the high peak current of Vishay TSAL5100 & TSAL6100 and their narrow beam angles, it would be my ideal choice if I was using a constant-current source that could safely drive near the peak current. But the Multicomp OFL-3102 is a lot cheaper and still looks quite decent, the only problem is that the OFL-3102 datasheet doesn't give much graphs of its behavior. I'm guessing it's capable of 500mA or similar peak current when driven by a pulse at 0.01 duty cycle for just a few microseconds, even if it's not shown in the datasheet. And it seems to have more radiant power at low currents compared to TSAL5100, and is slightly smaller. So I will try using the Multicomp OFL-3102 emitter LED, since it seems to be more efficient at 20-50mA that I'm expecting to drive it with, and the cost savings would be noticeable to someone in the 3rd world that might want this on 4 fingers with 4 LEDs. If I eventually find that the OFL-3102 with a current-limiting resistor doesn't give enough distance range or reliability, I might eventually switch to using a constant-current power source with the Vishay TSAL5100 LED in the future to get long-range measurements.