Harmon Fading LEDs have been around since 2004. They are very common to find.  CN and CP use this regularly and BNSF and UP have used it semi regularly. Most Light Rail Agencies also use this LED.

This LED comes in both a 12" and 8" form. The 8" form is not known to be use on newer installations. 12" is the most common. It's not known what kind of technology is used in this kind of LED. Red LED sidelights also come with this light.

The 12" model number is RG6-RTFB-48B for no sidelights. RG6-RTFB-48B-V1 for sidelights. 8" is RG4-RTFB-25B without sidelights. RG4-RTFB-43B with sidelights.

Temperature ranges for this kind of LED ranges from -40°C to +70°C (-40°F to +158°F), and operate from 8 to 20 volts D.C. and 8 to 16 volts A.C.

These LEDs appear to have been discontinued in favor of the newer design listed in the GE Uniform Look LEDs page.  Harmon seems to have now been absolved in GE entirely at this point.