Vishay Intertechnology BPW77NA Phototransistor Silicon Chip, NPN Transistor, Visible Light, 850 nm 3-Pin, 5.5 mm W x 6.15 mm H x 5.5 mm L (Pack of 2): Amazon.com: Industrial & Scientific
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Photo Transistor Light Sensor : ID 2831 : $0.95 : Adafruit Industries, Unique & fun DIY electronics and kits