When the bulb is on, the center circle of the color wheel can be used to adjust the brightness of the light bulb. If the light bulb is at 100% brightness, press your finger at the very top of the center circle and slide it down. As you slide down, the light bulb should become dimmer, and the percentage will decrease. When you are at the desired brightness, lift your finger. To make the bulb brighter, press your finger on the borderline between the color shades and slide up.