How to make pulsing texture (Sine) last longer when dull and not bright

How can I change the settings so when my texture pulses, the dull colour lasts longer than then it goes bright?
As we speak, I can lengthen the time the texture goes bright but not the reverse.

Do I 1-x the Sine?

1-sine just gives you another sine wave - try adding two sine waves together and offsetting one of them.