Infrared LED looks like an normal LED but you can not see it glowing. Transparent LED is a transmitter IR LED and it will transmit infrared light which is not visible to human eye, and dark black or blue LED is a photo diode or IR receiver LED. The package includes one Transmitter and one Receiver LED, size of LED is 5 mm. Receiver LED is also called photo diode. These are EVERLIGHT brand IR LED pair, for more details and technical specification see the datasheet.