Can you use the diffuser without having the lights on?

Sure, the light and mist function works separately, you can turn off the light by long pressing the LIGHT button about 2 seconds.

How long does this diffuser last on continuous use?

With full 500 ml water, strong mist can last 10 hours, weak mist can last 18 hours.

Can I use the diffuser without adding essential oils?

Yes, the oils are optional, you can use it without oils. It just like a humidifier without the oils.

Is it easy to clean?

Yes, the wide and large water tank is very easy to clean, just add some warm water and diluted vinegar, and lay it aside for 15 minutes, then use a wet cotton swab to clean the middle white disc of the tank. Then wipe with a soft cloth.

Is it quiet? I'm a light sleeper.