Morning is known to be their least favourite time of day. But teenagers struggling to get out of bed on time is nothing to do with their hormones or a need for extra sleep, researchers say. A study suggests most would be able to wake easily if they went outside more, then dimmed lights and stopped using smartphones and tablets at night. Surrey University and Harvard Medical School scientists found artificial light may be wholly to blame for Western teenagers rising late. Adolescents in hunter-gatherer tribes, who are outside all day and see light change naturally, get up at dawn. The study, in the journal Scientific Reports, looked at 25,000 Europeans and two African tribes. “It found teens were the age group most affected by light, and turning off blue light screens and dimming other lights could reset their body clocks.” Lead author Dr Anne Skeldon said, “This highlights that adolescents are not ‘programmed’ to wake up late and that by increasing exposure to bright light during the day, turning lights down in the evening and off at night should enable most to get up in time for work or school without too much effort and without changing school timetables.” She added, “Teenagers do not get much natural light, because they are in school all day, then, because it is easier for them than for other age groups to stay up late, they keep the lights on and use smart phones and tablets into the night. We know from previous research that blue light from these devices has a particularly strong effect on body clocks. If these teenagers were hunter-gatherers and were not exposed to this artificial evening light, most of them would sleep no later than anyone else.” Scientists have previously reassured parents their teenagers are not just lazy by stating that they have a biological predisposition to sleep late. However the British study, in collaboration with Harvard Medical School, suggests schoolchildren are making themselves more tired by sitting in front of electronic screens and keeping lights on at night. The problem may be getting worse as children are more tied to smart phones than ever before, while modern LED bulbs emit more blue light. The mathematical model on sleeping habits is based on a study of 25,000 European people and two hunter-gatherer tribes in Namibia and Tanzania. The researchers wanted to see if shifting school start times later, allowing teenagers to sleep for longer, would help with ‘social jetlag’ – which cause them to sleep later at the weekend after becoming deprived during the week. But the study found most teenagers’ clock would drift even later in response to the later start time, and in a matter of weeks they would find it just as hard to get out of bed. Instead, it concludes that children, and particularly night owls, would sleep better with less light at night. The study, published in the journal Scientific Reports, concludes that “the profound delay in sleep observed in adolescents in modern industrialised societies is largely a result of our ability to self-select patterns of light exposure”.