Well, I do leave it on all day, but catch far more at night, as it can be seen much more in the dark, throughout the rooms. I think the bulb lasts longer if you don't turn it on and off all the time as well. You get an extra bulb with the unit as well.
The specific wavelength that works cannot come from an LED bulb, so ignore cheaper LED models. You must use this one.
Remember, it attracts mosquitos, so you must put it away from you, otherwise the mossies will be drawn towards the light, then veer over to you for a meal instead.
I have never seen anything so effective on mossies as this unit. I have 3 throughout the house in different locations.