An LED lamp, comprising: a die substrate (14, 16, 40); wherein the substrate has formed thereon a semiconductor material (12, 13); an electrode for the application of a bias across the semiconductor material for causing light to be emitted therefrom; and an adhesive (17, 22) that bonds the die substrate to a support substrate (19,30,42); wherein the adhesive is a polymerized siloxane polymer having a thermal conductivity of greater than 0.1 watts per meter kelvin (W/(m·K)), and wherein the polymerized siloxane polymer has silicon and oxygen in the polymer backbone, as well as aryl groups bound thereto, wherein and characterized in that the polymerized siloxane polymer is a polymerization product of at least a first compound, a second compound and a fourth compound, wherein the first compound has a chemical formula: SiR 1 aR 2 4-a where a is from 1 to 3, R 1 is a reactive group, and R 2 is an alkyl group or an aryl group; wherein the second compound has a chemical formula SiR 3 b R 4 c R 5 4-(b+c) where R 3 is a cross-linking functional group, R 4 is a reactive group, R 5 is an alkyl group or an aryl group, and b = 1 to 2, and c =1 to (4-b); wherein the fourth compound has a chemical formula: R 2 3-a R 1 a SiR 11 SiR 1 b R 2 3-b where a is from 1 to 3, b is from 1 to 3, R 1 is a reactive group, R 2 is an alkyl group or an aryl group and R 11 is an alkyl group or an aryl group, with the proviso that at least one of the first compound, the second compound and the fourth compound has an aryl group; and wherein the adhesive further comprises particles having an average particle size of less than 10 microns; wherein the particles comprise a late transition metal selected from groups 8 to 11 of the periodic table; and wherein the adhesive is not light absorbing and transmits or reflects at least 80 % of visible light incident thereon. a die substrate (14, 16, 40); wherein the substrate has formed thereon a semiconductor material (12, 13); an electrode for the application of a bias across the semiconductor material for causing light to be emitted therefrom; and an adhesive (17, 22) that bonds the die substrate to a support substrate (19,30,42); wherein the adhesive is a polymerized siloxane polymer having a thermal conductivity of greater than 0.1 watts per meter kelvin (W/(m·K)), and wherein the polymerized siloxane polymer has silicon and oxygen in the polymer backbone, as well as aryl groups bound thereto, wherein and characterized in that the polymerized siloxane polymer is a polymerization product of at least a first compound, a second compound and a fourth compound, wherein the first compound has a chemical formula: SiR 1 aR 2 4-a where a is from 1 to 3, R 1 is a reactive group, and R 2 is an alkyl group or an aryl group; a is from 1 to 3, R 1 is a reactive group, and R 2 is an alkyl group or an aryl group; wherein the second compound has a chemical formula SiR 3 b R 4 c R 5 4-(b+c) where R 3 is a cross-linking functional group, R 4 is a reactive group, R 5 is an alkyl group or an aryl group, and b = 1 to 2, and c =1 to (4-b); R 3 is a cross-linking functional group, R 4 is a reactive group, R 5 is an alkyl group or an aryl group, and b = 1 to 2, and c =1 to (4-b); wherein the fourth compound has a chemical formula: R 2 3-a R 1 a SiR 11 SiR 1 b R 2 3-b where a is from 1 to 3, b is from 1 to 3, R 1 is a reactive group, R 2 is an alkyl group or an aryl group and R 11 is an alkyl group or an aryl group, a is from 1 to 3, b is from 1 to 3, R 1 is a reactive group, R 2 is an alkyl group or an aryl group and R 11 is an alkyl group or an aryl group, with the proviso that at least one of the first compound, the second compound and the fourth compound has an aryl group; and wherein the adhesive further comprises particles having an average particle size of less than 10 microns; wherein the particles comprise a late transition metal selected from groups 8 to 11 of the periodic table; and wherein the adhesive is not light absorbing and transmits or reflects at least 80 % of visible light incident thereon.