From now on, environmentally-conscious travellers can feel less guilty when taking the Tsuen Wan MTR line. The difference is undetectable to the naked eye, but the Kowloon line is the first to fully install High Brightness Light Emitting Diode (HB-LED) lights inside all its carriages. This follows a successful trial in 2006, where only one of the 24 carriages was fitted with the lights. HB-LED lights are costly, but highly energy-efficient. They consume 20-30 per cent less electricity than fluorescent tubes, last three times longer, and unlike conventional lights, do not contain toxic mercury substances. When the mercury in conventional fluorescent breaks in landfills, it poisons the air, the soil and the streams around it. The lights were developed by the Hong Kong University of Science and Technology (HKUST) and the MTR Corporation. In the future, the MTR Corporation says it will install HB-LED fixtures in at least two more lines, the train stations and in-station advertising boxes. Calling it a 'visionary' achievement, HKUST's dean of engineering, Philip Chan, added that there was still room for growth in the use of this greener technology. 'There is no doubt that one of these days HB-LED SSL will become the mainstream of general lighting in most households.'