We have seen a shift in office lighting from a traditional 4 tube lay in panel with louvre to 600x600 LED Panels with a thermoplastic diffuser . A thermoplastic material is one that can be remoulded and becomes liquid in form when heated as opposed to a Thermosetting plastic that degrades when heated , a good example of a thermosetting resin is bakelite. LED Panels use thermoplastic diffusers to direct light from an LED Panel.
600x600mm LED Panels are designed to fit into a grid ceiling and offer 50% saving in electricity when compared to a fluorescent tube and louvre set up.
Fire safety part B mentions the use of thermoplastic materials and states that ceilings of rooms and circulation spaces may incorporate thermoplastic lighting diffusers but there are conditions.
When it is a requirement to comply with Fire safety Part B of the Building regulations 2 types of diffuser have been developed TPa and TPb to ensure the installation is compliant.