Philips produced a variation on the HMI, a single-ended version called MSR/HR (medium source rare-earth hot-restrike). It uses a standard two-prong lampbase. In order to avoid the colour shift during use they added a secondary envelope around the gas-chamber. Several other bulb variations exist, including GEMI (General Electric metal iodide), CID (compact indium discharge; Thorn EMI, UK, since 1990 GE), CSI (compact source iodine; Thorn EMI, UK), DAYMAX (made by ILC), and BRITE ARC (|Lighting Inc. (SLI)). All are variations on, and different names for, essentially the same concept.