Sydney, Jan 9 (IANS): Children who spend too much time on tablets, mobile phone or television are more likely to gain unhealthy weight not just because of physical inactivity but also due to increased exposure to light, says a new study.

Timing and intensity of light exposure is critical for metabolic functioning and weight status, the findings showed.

"Artificial lighting, including light given off by tablets, mobile phones, night lights, and television, means modern children are exposed to more environmental light than any previous generation. This increase in light exposure has paralleled global increases in obesity," said said one of the researchers Cassandra Pattinson from Queensland University of Technology in Brisbane, Australia.

Researchers studied children aged three to five, from six Brisbane childcare centres.

They measured children's sleep, activity and light exposure for a two week period, along with height and weight to calculate their body mass index (BMI), then followed up 12-months later.

At the initial measurements, the researchers found that moderate intensity light exposure earlier in the day was associated with increased body mass index while children who received their biggest dose of light -- outdoors and indoors -- in the afternoon were slimmer

At follow-up, children who had more total light exposure at the beginning had higher body mass 12 months later.

"The circadian clock -- also known as the internal body clock -- is largely driven by our exposure to light and the timing of when that happens. It impacts on sleep patterns, weight gain or loss, hormonal changes and our mood," Pattinson explained.

This research suggests that exposure to different types of light (both artificial and natural) at different times now needs to be part of the conversation about the weight of children.

The study was published in the journal PLOS ONE.