IEA 4E notes on data from UK mapping and benchmarking report:
a) 1999-2010: Projections derived from annual sales values based on modelling (although with supporting verification). Data supplier views the sales values provided as relatively  robust (with some caveats) for all domestic (household) sector lamps used in the residential sector only
b) 2011-2013: Based on annual sales data by lamp type scaled up (linearly) to account for estimated market coverage of approximately 80-90% for all lamps and 60-70% for LEDs