in illuminated areas , thereby having a negative impact on ecosystems . Under dark conditions fruit bats would produce a copious rain of seeds that would help rain forests recolonize land that had previously been cleared . Conservationists therefore recommend that dark refuges be connected by dark corridors to reduce the impact of light pollution by enabling bats to migrate from one sensitive area to another . Not only does lighting affect animals , but it also affects plants . Many flying insects are important as pollinators , and with insect populations declining , this is reducing the number of successful pollinations . This will have the effect of reducing plant numbers and diversity , and this will further backfire on insects dependant on plants for food , in a positive feedback cycle of ever spiralling decline . Many crops depend of insects for pollination , so this could ultimately affect crop yields . Consequently , farmers will not want street lighting in rural areas where they grow their crops . Light at night can also affect germination , flowering and abscission cycles in plants by interfering with phytochrome production , thereby preventing plants from adjusting to the seasons . Phytochromes are plant hormones that govern photoperiodism in plants enabling them to measure the hours of darkness and anticipate when to bloom , produce seeds , or drop their leaves in autumn . Disruption of phytochrome production will again have serious implications for crop production , such as strawberry plants failing to bloom . Deciduous trees exposed to artificial light tend to retain their leaves in winter . If normal photoperiodism is disrupted , then this will lead to further declines in plant diversity and concomitant effects on animals dependant on them for food . This could well include ourselves . Many animals are also dependant on trees for their natural habitat , so if trees are adversely affected they will have nowhere to live and consequently their numbers
will decline . Photoperiodism in plants requires exposure to visible red light ( 625 to 760nm , and infrared ( 760nm to 850nm ). Artificial lighting , particularly towards the red end of the spectrum such as sodium lighting , will therefore have an effect on photoperiodism in plants . This includes trees 6 . Lighting is now known to advance budburst in deciduous trees in the U . K . by 7.5 days 7 . Earlier budburst may further have an impact on those animal species dependent on the trees for food and habitation . Photosynthesis depends on shorter 15 wavelength light ( blue – 400 – 450nm and red – 625 – 700nm ). Green light has little or no effect on plants as this is largely reflected by the green pigment chlorophyll . Artificial light is not intense enough to affect photosynthesis , but orange lighting from street lights extends day-length , affects flowering patterns , and extends the period of growth into winter when the plant can be damaged by frosts and low temperatures . Furthermore continuous lighting is more damaging than part-time lighting . Human health is also affected by lighting . Until the advent of electric
lighting humans tended to retire to their homes during the hours of darkness . Any lighting that was available was unobtrusive , such as candles and oil lamps that have a low blue light component . With the advent of electric lighting , daylight can be extended into the hours of darkness , and if the light is rich in blue light , it can suppress melatonin production by the pineal gland , located in the brain . Melatonin helps to regulate circadian rhythms in humans and other animals , and if this is disrupted , can have a disturbing effect on the individual affected . In addition , melatonin is oncostatic , meaning it suppresses cancers 8 . This occurs through interfering with the Warburg Effect 9 that affects respiration in tumour cells . It has been reported that the incidence of breast and prostate cancer is more prevalent in areas that are lit up all night , as compared to those areas where it is dark . Reductions in bat populations may cause mosquito numbers to rise , possibly leading to the spread of mosquito-borne diseases such as malaria , filariasis , dengue fever , and Japanese encephalitis 10 . These diseases may then spread into areas
COURTESY
Road safety on motorways can be guaranteed by less intrusive methods such as reflective road studs ( above ) or cat ’ s eyes ( inset ).
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