Riker had to turn up his phaser-2 so that all the glowy lights were on, in The Vengeance Factor. I thought that was pretty dramatic.
Yup, 8+8 green lights. Whether this means setting 8 or setting 16, we might debate. After all, in "Frame of Mind", Riker says setting 16 should remove half a building, and Worf uses the setting for blasting away a lot of rock in "Chain of Command". OTOH, backstage material says that setting 8 is the lowest that will remove the target from existence - thus the setting Riker would need to put Yuta out of her misery, without a smidgen of overkill.
Perhaps the lights turn red for settings 9-16?