A thin, flat light emitting diode luminaire, comprising: an LED bar having at least one light emitting diode disposed thereon; an optical stack having an edge that abuts the LED bar, including, from top to bottom: a flat baseboard, a flat reflection panel for receiving light from the LED bar; a flat acrylic panel having a top surface and a bottom surface, the top surface facing flat reflection panel, the top surface having a mask pattern printed thereon, the mask pattern being configured to differentially couple light transmitted from the flat reflection panel into the flat acrylic panel for providing a uniform transmission of the light from the acrylic panel across the bottom surface of the flat acrylic panel, and a flat diffusion panel configured to receive the light from the bottom surface of the flat acrylic panel and emit the light into a space to be illuminated characterized in that the LED bar is positioned so that it emits light into the edge of the flat reflection panel, and in that the mask pattern is printed with interconnected meshing dots, the printed pattern of meshing dots being less dense further from the LED bar and more dense closer to the LED bar so as to differentially couple more light closer to the LED bar and less light further from the LED bar to provide for uniform transmission of light from the acrylic panel across the bottom surface of the flat acrylic panel. an LED bar having at least one light emitting diode disposed thereon; an optical stack having an edge that abuts the LED bar, including, from top to bottom: a flat baseboard, a flat reflection panel for receiving light from the LED bar; a flat acrylic panel having a top surface and a bottom surface, the top surface facing flat reflection panel, the top surface having a mask pattern printed thereon, the mask pattern being configured to differentially couple light transmitted from the flat reflection panel into the flat acrylic panel for providing a uniform transmission of the light from the acrylic panel across the bottom surface of the flat acrylic panel, and a flat diffusion panel configured to receive the light from the bottom surface of the flat acrylic panel and emit the light into a space to be illuminated characterized in that the LED bar is positioned so that it emits light into the edge of the flat reflection panel, and in that the mask pattern is printed with interconnected meshing dots, the printed pattern of meshing dots being less dense further from the LED bar and more dense closer to the LED bar so as to differentially couple more light closer to the LED bar and less light further from the LED bar to provide for uniform transmission of light from the acrylic panel across the bottom surface of the flat acrylic panel. a flat baseboard, a flat reflection panel for receiving light from the LED bar; a flat acrylic panel having a top surface and a bottom surface, the top surface facing flat reflection panel, the top surface having a mask pattern printed thereon, the mask pattern being configured to differentially couple light transmitted from the flat reflection panel into the flat acrylic panel for providing a uniform transmission of the light from the acrylic panel across the bottom surface of the flat acrylic panel, and a flat diffusion panel configured to receive the light from the bottom surface of the flat acrylic panel and emit the light into a space to be illuminated characterized in that the LED bar is positioned so that it emits light into the edge of the flat reflection panel, and in that the mask pattern is printed with interconnected meshing dots, the printed pattern of meshing dots being less dense further from the LED bar and more dense closer to the LED bar so as to differentially couple more light closer to the LED bar and less light further from the LED bar to provide for uniform transmission of light from the acrylic panel across the bottom surface of the flat acrylic panel.