Sine Wave vs Square/Pulse Wave

I was curious to hear peoples thoughts on the whole gradual on/off vs sudden on/off of the led's in light and sound. I brought up the topic in another thread, but wanted to expand on the idea.

On one of my machines most of the programs use gradual on/off, and I know a lot of modern manufacturers are using a lot of this sine wave in their programming.

I was watching the old NTF lectures and in one of them Julian Isaacs spoke about research showing that sudden on/off lights had more of an entrainment effect as they jolted all the nerves in the eyes on/off at the same time. I was curious if later research showed that this was not the case, or what pushed manufacturers into using more gradual on/off sine wave functions instead of sudden on/off square/pulse wave programming.

Any and all thoughts and information are appreciated!

Square waveforms can cause harmonics in the brain, so when using sessions that are meant to calm you such as alpha or theta, you can also be stimulating harmonics in the beta range, which will be counter productive. This is not usually a problem when stimulating beta or gamma, but pure square wave forms can be harsh.

I have been told that light modulated by square waves does tend to produce at least one higher harmonic on an EEG monitor. I have not observed this directly. Sine waves are 'purer' in a sense and more targeted. Smooth sloping waveforms also are more pleasant at low frequencies and for color mixing.

There is a noticeable difference when you stack two colors on top of each other on the Procyon with one set to a square and the other to a sine wave. The square is more intense while the sine has a spike.