The diffuser can give out strong and weak mist and it is easy to do. You do not need to get eye irritation first to know if the mist is strong or not. It is not even reliable. But one thing is for sure, if the scent has become too much, your air passage will start to get irritated and you will develop an adverse reaction. To prevent this from happening, you can set the mode of the diffuser to strong or weak. Just press the high and low button and you’ll hear a beep. One beep means strong and two beeps mean weak. If the diffuser contains 500 ml of water, on strong mist mode it can run for 10 hours. If the diffuser is on weak mist mode it can run for as long as 16 hours.