For green activists with an eye for energy issues, one of the easiest targets is light bulbs. Most of the bulbs we use in our homes are not energy efficient and that means increased carbon emissions. Greenpeace and other environmental watchdogs have been pushing hard for the Hong Kong government to follow the lead of other countries and regions, such as Australia, Chile and the European Union, and phase out traditional incandescent light bulbs to make way for their green equivalents. The argument seems compelling. In 2007, Greenpeace put the case that replacing incandescent light bulbs with compact fluorescent light bulbs (CFLs) - as the pricier green bulbs are known - would cut carbon dioxide emissions by 480,000 tonnes in the city annually. Small surprise then that, while the campaign has not been a success in making CFLs mandatory, Hong Kong consumers have begun to embrace the green light sources. According to the Environment Protection Department, an estimated 3.5 million CFLs are sold annually in the city. The downside is that the department also estimates that up to 3 million used CFLs are discarded every year. 'Green' CFLs contain minute amounts of mercury - around 5mg per bulb on average. Mercury is extremely toxic. It is dangerous even in small quantities because if it is inhaled or absorbed through your skin, it affects the central nervous system. When the bulbs are thrown away and leak into landfills, over time, the mercury can find its way into the soil and enter the food chain. 'CFLs contain mercury, which is poisonous,' admits Man Chi-sum, chief of Hong Kong environment watchdog Green Power. 'When a bulb breaks at home, children should be kept away from the pieces.' One British government advisory has gone further, urging people to leave and seal up any room in which a CFL breaks for 15 minutes. The United States Environmental Protection Agency presents a less dramatic solution in the event of a breakage, advising: 'Open nearby windows to disperse any vapour that may escape, carefully sweep up the fragments [do not use your hands] and wipe the area with a disposable paper towel to remove all glass fragments. Do not use a vacuum [cleaner]. Place all fragments in a sealed plastic bag.' The question then is what to do with the sealed plastic bag. If it ends up in a landfill, as likely most of the estimated 3 million CFLs that are thrown away in Hong Kong every year do, the sealed bag will eventually release its toxic contents. In Hong Kong, any site that stores more than 500 units of lighting that contain mercury - including CFLs - is required by law to have used and broken bulbs disposed of at a chemical waste treatment centre in Tsing Yi. It separates the mercury, recycles it, and the bulb pieces are treated before disposal in landfills. But there are no similar requirements on households. The city only has a voluntary scheme that was launched by the Environment Protection Department in 2008 to collect CFLs. The scheme involves 760 housing estates and 67 shopping malls and household product shops, all of which have collection boxes for used CFLs lamps. The target is to collect 400,000 used CLFs a year. The department advises that used bulbs should be wrapped in their original packaging or the packaging that came with bulbs that replaced them. It suggests broken bulbs be sealed in plastic bags and that handlers wear rubber gloves. But concern group Greeners Action says the current programme is not enough and that the government should consider making it compulsory to recycle CFLs. 'The energy-saving light bulbs are becoming more popular, and solely relying on a voluntary recycle scheme is not enough,' a spokesman for the group said. 'The annual recycle target of 400,000 bulbs is low compared with the number we throw away.' Meanwhile, there have been reports in the Chinese and Western media of mainland workers who manufacture CFLs suffering from chronic and acute mercury poisoning. According to Chinese-language news site Securitimes.com, tests on 500 employees working at Foshan Electronics Zhaoming Ltd in Guangdong province revealed that nine employees were suffering from chronic mercury poisoning, while 143 tested over the safe limit. The company manufactures both regular fluorescent lights and CFLs. The Times of London quoted one young female employee as saying: 'In tests, the mercury content in my blood and urine exceeded the standard but I was not sent to hospital because the managers said I was strong and the mercury would be decontaminated by my immune system.' Greenpeace campaign manager, Edward Chan Yue-fai, said the organisation was not aware of any incidents of workers manufacturing CFLs being poisoned. In the meantime, most experts agree that over the long term CFLs are better for the environment than traditional incandescent bulbs. Coal smoke stacks - the world's main energy source - for example, emit far more mercury toxins than broken and discarded CFLs. All the same, critics point out, one of the green movement's most oft-touted quick fixes may not be quite as green as we have been led to believe. Additional reporting by Zoe Mak