Super Sprouter's 7" Ultra Clear Vented Humidity Dome have built-in light tracks that accommodate the 18" T5 grow lights. 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. Please note, our automatic shipping software is not well calibrated for bulk purchases of this item. If you are looking to purchase more than 3, please contact us at orders@halifaxseed.ca. For the most streamlined process, please include a screenshot of the items in your cart, your mailing address, and phone number. We will contact you via phone to process payment.