coating 30 can be the ammonium salt of acrylic methacrylic acid acrylic methacrylic ester copolymer preferably of high molecular mass if a coating containing such a water resistant binder is dried e g at a temperature of at least 80 degrees c it becomes sufficiently water resistant to survive a subsequent water based coating step without being washed off thus the phosphor coating 30 can be made partly water insoluble by drying a wet phosphor coating 30 with hot air at 80 degrees c or above as schematically shown in fig4 the step 41 of providing a phosphor coating 30 on the inner surface 13 of the envelope 12 desirably may also include the step of wash proofing the phosphor coating 30 as schematically represented in fig4 methods for making a light source 10 may include a step 42 of providing a protective coating 14 on the inwardly facing surface 31 of the phosphor coating 30 as schematically shown in fig2 and 3 the protective coating 14 defines an innermost surface 15 that may make possible the effective recombination of hg ions on the innermost surface 15 of the protective coating 14 to inhibit the collision of hg ions with the phosphor particles 32 in the phosphor coating 30 the radial thickness range of the protective coating 14 may be a value between about 0 01 micrometers and about 5 micrometers other thicknesses are possible in certain embodiments the protective coating 14 should be transparent to visible light and as transparent to 254 nm uv light as possible certain materials can help the coating 14 fulfill both requirements for.