5mm emitting diode that looks like a 5mm LED & has a blue transparent lens. Mechanically and spectrally matched to the infrared phototransistor (PHOTOIRR5).

Features:
- Viewing Angle: 30°
- Peak Spectral Wavelength(IR): 940nm @ 20mA 
- Spectral Bandwidth (DI): 50nm@20mA
- Material: GaAs
- Optocoupler Operating Current: 50mA
- Reverse Voltage: 5V
- Forward Voltage: 1.2

See datasheet here.