Luminescent light diffuser for diffuse lighting applications.

The lighting industry currently accounts for a significant proportion of all energy demand. Luminescent white lighting is often impure, inefficient, expensive, and detrimentally emits as a point source, meaning the light is emitted from a focused point. A luminescent light diffuser offers the potential to create a spatially broad lighting fixture. We developed a luminescent light diffuser consisting of three commercially available luminescent dye species (rhodamine 6G, fluorescein, 7-diethylamino-4-methylcoumarin) dispersed within a polymer matrix (polyvinyl alcohol), or commercial paint, and coated on a planar waveguide. A Light-emitting diode (LED) (385 nm) is directed into the waveguide which excites the luminescent species, coating the panel, creating a device that emits spatially broad pure white light. As the emission depends on escape cone emission from the waveguide, the device's emission was found to depend highly on the coating film quality and components. We present two systems: a small 40 mm × 40 mm prototype, made using standard water-soluble polymer (polyvinyl alcohol), to study the underlying operational principles, and a 100 mm 100 mm device with optimized efficiency fabricated with a clear commercial paint. By doping the polymer matrix with scattering silica microparticles we achieved a maximum photon outcoupling efficiency of 78%, whilst maintaining colour purity with an increased device size of more than 300 times (compared with the input LED). This work shows that it is possible to construct an inexpensive and spatially broad lighting source, whilst maintaining colour purity at a low cost.