Size: Diameter: 495mm / 19.5", Fits 20 inch Lampshade Openings(Please confirm the inner diameter of the lampshade before purchase). Advantage: Made of 1/8 inch (2.7mm) thick DOUBLE SIDED double smooth white acrylic sheet with a 3/8" (10mm) center hole. this diffuser is thicker than other diffuser and can withstand the heat generated by the lamp. It has good light transmittance, durability, heat resistance, and long service life. Application: This diffuser can soften and diffuse the light of the bulb, is great for eliminating glare from CFL or LED bulbs, and improves visual comfort by reducing eyestrain, creating more comfortable, eye-friendly lighting. You can also use it to direct light downward for accent or improved reading light. It provides soft and evenly distributed light, creating a pleasant and comfortable reading and working atmosphere in your living space. Instruction: Just directly put the acrylic board on the top or bottom of the lampshade. Dual use for mounting on top of your table lamp shade or floor lamp shade or fits the top or bottom of most hanging drum-style pendant light fixtures. NOTE: 1. Please tear off the transparent protective film of the product before installation. 2. When the Lampshade Diffuser is installed at the top of the desk lamp cover, to avoid overheating your lamp leave a little room on the edge to let heat escape