Q: Lights for the dashboard are not very effective

Your issue is somewhat unique and may be difficult to diagnose, mostly because of the random nature of its occurrence. That being said, it is important to look at other things that are happening at the same time of the dim lights. Are there any warning lights, has the passenger made any adjustments to seat settings, HVAC (heating, ventilation, air-conditioning) temperature or other? These may give the technician who will diagnose your issue something to go on. When the lights dim, can you change them using the dash dimmer? If so, there may be an issue in the switch itself, but this is the most unlikely cause. My recommendation is to carefully dissect the pieces of the issue when it happens. Pay attention to the other lights like the HVAC control panel, the lights in the switches on the doors, even turn on the overhead reading lamps to see if the dim lights are just on the dashboard, or if the whole interior is affected. My first instinct makes me guess that the issue is internal to the instrument cluster itself.