The PT481 family, from Sharp, are a family of narrow acceptance phototransistors. They are in side looking (SL) epoxy resin packages with a domed lens on the side of the package. The PT481F devices have a black plastic package which offers a daylight blocking filter while the PT481 has a clear lens for visible and near IR radiation.
Features of the PT481 phototransistors:
Side looking (SL) package
Through-hole mounting
Clear or black plastic package