From VOA Learning English,

this is the Health Report.

Some colors that people see

late at night could cause signs

of the condition mental health experts call

clinical depression.

That was the finding of a study

that builds on earlier study findings.

They show that individuals

who live or work in low levels of light overnight

can develop clinical depression.

Doctors use the words clinical depression

to describe severe form of depression.

Signs may include loss of interest

or pleasure in most activities,

low energy levels and thoughts of death or suicide.

In the new study,

American investigators designed an experiment

that exposed hamsters to different colors.

The researchers chose hamsters

because they are nocturnal,

which means they sleep during the day

and are active at night.

The animals were separated into 4 groups.

One group of hamsters was kept in the dark

during their nighttime period.

Another group was placed in foldable blue light,

a third group slept in foldable white light.

While a fourth was put in foldable red light.

After four weeks, the researchers noted

how much sugary water the hamsters drank.

They found that the more depressed animals

drank the least amount of water.

Randy Nelson heads the Department of Neuroscience

at Ohio State University.

He says animals that slept in blue and white light

appeared to be the most depressed.

"What we saw is these animals didn't show

any sleep disruptions at all

but they did have mucked up circadian clock genes

and they did show depressive phenotypes

whereas if they were in the dim red light, they did not."

Randy Nelson notes

that photosensitive cells in the retina,

have little to do with eyesight.

He says these cells send signals

to the area of the brain that controls

what has been called the natural sleep-wake cycle.

He says there's a lot of blue in white light,

this explains why the blue light and white light hamsters

appear to be more depressed

than the hamsters see red light or darkness.

Mr Nelson has suggestions

for people who work late at night,

or those who like to stay up late.

"My recommendation is

if you are just living a typical

mostly active [life] during the day,

mostly inactive at night,

you want to limit exposure to TVs which are quite bluish

in the light they give off

and computer screens and things like that.

You can get filtered glass,

you can get filters on your computer screen

and filters on your eReaders

to put it more in the reddish light."

The report on the effects of light on emotions

was published in The Journal of Neuroscience.