A light source (32, 60, 80) for a spatially variable backlight in a thin display comprising: a light-emitting layer (62,84A) operative to emit light in response to an electrical potential difference being applied across the light-emitting layer (62, 84A), the emitted light having an intensity dependent upon the magnitude of the potential difference; a first electrode structure (63, 84B) comprising a first transparent, electrically-conductive electrode (63, 84B) on a first face of the light-emitting layer (62, 84A) that faces towards a viewer; a second electrode structure (64, 81, 83) arranged on a second face of the light-emitting layer (62, 84A) opposite to the first face of the light-emitting layer (62, 84A); characterized in that the second electrode structure (64, 81, 83) comprises a layer of a potential-distributing material (67, 83) having an electrical resistance and an array of control points (65, 81), the control points (65, 81) comprising second electrodes (65, 81), wherein the layer of potential-distributing material (67, 83) and the array of control points (65, 81) are both arranged on and in electrical contact with the second face of the light-emitting layer (62, 84A), and wherein the layer of potential-distributing material (67, 83) is both in electrical contact with and extends between the second electrodes (65, 81), the second electrodes (65, 81) being arranged at locations spaced apart over the second face of the light-emitting layer (62, 84A); wherein the potential-distributing material (67, 83) is arranged to distribute electrical potentials applied to the second electrodes (65,81) of the second electrode structure (64, 81, 83) over the light-emitting layer (62, 84A). a light-emitting layer (62,84A) operative to emit light in response to an electrical potential difference being applied across the light-emitting layer (62, 84A), the emitted light having an intensity dependent upon the magnitude of the potential difference; a first electrode structure (63, 84B) comprising a first transparent, electrically-conductive electrode (63, 84B) on a first face of the light-emitting layer (62, 84A) that faces towards a viewer; a second electrode structure (64, 81, 83) arranged on a second face of the light-emitting layer (62, 84A) opposite to the first face of the light-emitting layer (62, 84A); characterized in that the second electrode structure (64, 81, 83) comprises a layer of a potential-distributing material (67, 83) having an electrical resistance and an array of control points (65, 81), the control points (65, 81) comprising second electrodes (65, 81), wherein the layer of potential-distributing material (67, 83) and the array of control points (65, 81) are both arranged on and in electrical contact with the second face of the light-emitting layer (62, 84A), and wherein the layer of potential-distributing material (67, 83) is both in electrical contact with and extends between the second electrodes (65, 81), the second electrodes (65, 81) being arranged at locations spaced apart over the second face of the light-emitting layer (62, 84A); wherein the potential-distributing material (67, 83) is arranged to distribute electrical potentials applied to the second electrodes (65,81) of the second electrode structure (64, 81, 83) over the light-emitting layer (62, 84A).