Products in the phototransistor family are discrete light sensitive components which behave in similar fashion to a bipolar transistor, but use incident light instead of an electrical current applied through a device terminal to cause the device to conduct. Compared to photodiodes, phototransistors generally produce a much larger output current for the same intensity of incident light, though are slower to respond to changes in light intensity. These differences result in phototransistors being simpler to apply, but less useful for high speed operation.