These excellent quality 4 in and 7 in Ultra Clear Vented Humidity Domes now have built-in light tracks that accommodate the 18 in Super Sprouter? T5 HO Grow Light Fixture. The light tracks are directional to allow the light to run the length of the domes or the width of the domes, allowing two trays to run side by side. Vertical sides allow the use of all plant sites in a propagation tray. Two vents in the top of the dome can be opened or closed to control humidity. These are the most clear and transparent domes on the market, allowing for maximum light penetration and the best viewing of your plant starts.