Your worst spending decisions could be on a bright sunny day, says study

The amount of light that falls on the Earth's surface may affect your spending behaviour and financial decision-making, a study suggests.

Researchers at the University of Sydney in Australia found that luminance affects decision-making in different ways.

Luminance is a measurement of the amount of light that falls on the Earth's surface, which can be affected by cloud cover, humidity, suspended particles, and time of day and year.

Higher and lower levels of light intensity were found to affect how much risk people can tolerate, how comfortable they are making decisions in ambiguous situations, and how consistent their decisions are over a range of choices.

The team found that on the days with higher light intensity, people made worse decisions and they were more inconsistent in the choices that they made.

Researchers also found that luminance also affected people's risk attitudes. When the luminance level was high people were more likely to avoid known risks.

When offered a choice between a certain USD 5 payout and a 50 per cent chance of USD 20, they were more likely to go for the certain USD 5.

People had a greater tolerance for unknown risks. On high luminance days, they were more likely to go for an unknown chance of getting USD 20 over the certain USD 5 payout, researchers said.

"Overall, the effects are not of an enormous magnitude, but nevertheless they are consistent, significant, and strong enough to be expected to have significant effects on financial markets," said Agnieszka Tymula, associate professor at the University of Sydney.

Researchers investigated how luminance affected 2,530 people's decisions about monetary gambles. 

They asked people to make 40 monetary decisions, using touch screens mounted at an exhibition on ageing at the National Academy of Science Museum in Washington DC.

In each situation, people could choose a certain payout of USD 5, or a lottery option with the possibility of receiving nothing, or a cash amount between USD 5 and USD 125.

Behavioural data from the responses received at the museum was then merged with luminance measurements from a nearby weather station.

The study was published in the journal PLoS ONE.