half tones should go on a higher mesh like a 200 i use a 230 my self, the reason for that is, is because it's a tighter mesh and only pushes so much ink through so you can keep your detail, as for a 110 the holes are bigger so more ink goes through.
When burning halftones, do you increase or decrease burn time. Do you increase or decrease screen mesh. 155 would be an increase to 110.
What wattage bulb are you using to expose for only 2 minutesThe amount of exposure time will depend on the type of emulsion and mesh and color of mesh. For instance if I am doing halftone work with 110 155 my lpi would be 35 or less for the screen to be able to burn the halftone. But the higher mesh counts you use then you can you can increase your lpi. As for burn times for halftone work with 110, 155, I use the same exposure time as if I were using solid spot color screens. But once I use the 230 my mesh color is yellow for those higher mesh counts, which means if you use a yellow, the light scatters and you have to bump up your exposure time to compensate the light scattering. Usually I burn screens for 2:00 minutes and when I use the higher mesh counts I burn for 2:15 that 15 seconds is just enough time for the screen to burn correctly. Just have to play with it and find your right times.