Optical pickups are another type of non-magnetic pickup. They use an infrared LED to optically track the movement of the string, similar to the mechanism of modern computer mice, which allows them to reproduce low-frequency tones at high volumes without the "hum" or excessive resonance associated with conventional magnetic pickups. Since optical pickups do not pick up high frequencies or percussive sounds well, they are commonly paired with piezoelectric pickups to fill in the missing frequencies. LightWave Systems builds basses with optical pickups.
Maybe you've already got a specific brand in mind and want to see all the digital pianos they offer. All you have to do is click on the brand on the left hand side of the screen and within a few moments you'll have access to everything that's available. For that matter, you can always play is safe and stick to the top-rated items…and there are plenty of those in this selection.