What is the term for the older dimmers, like those pioneered by Spira, that chop the beginning of the AC waveform?

Answer

Leading-edge dimmers

Dimmer switches that chop the beginning segment of the alternating current waveform are known as leading-edge dimmers.

What is the term for the older dimmers, like those pioneered by Spira, that chop the beginning of the AC waveform?
inventioninventorlightLEDDimming