Exposure to bright light can lead to greater sexual satisfaction in men who have low sexual desire, a new study suggests.
Scientists from the University of Siena in Italy found that using a light box, similar to those used to treat some forms of depression, increased testosterone levels.
And this led to greater reported levels of sexual satisfaction.
But they said more research was needed before it could be used as a treatment.
The researchers carried out their study on 38 men who had been diagnosed with disorders which cause a lack of interest in sex.
One half of the group was treated with a light box, while the other half was treated with an adapted light box which gave out significantly less light.
They were treated for half an hour early in the morning for two weeks.
When they retested the participants, they found that the group exposed to the bright light tripled their sexual satisfaction scores while the control group's scores stayed roughly the same.
The researchers also found that testosterone levels increased in men who had been given the active light treatment from around 2.1 ng/ml to 3.6 ng/ml - but the control group showed no increase.
Prof Andrea Fagiolini, who led the study, said the increased levels of testosterone explained the greater reported sexual satisfaction.
What is light box treatment?
Light therapy is where a special lamp called a light box is used to simulate exposure to sunlight.
A light box contains very bright fluorescent tubes - usually at least 10 times the intensity of household lights.
They are commonly used to treat Seasonal Affective Disorder.
A patient looks into the light box and when light hits the back of the eye, messages are passed to the part of the brain that controls sleep, appetite, sex drive, temperature, mood and activity.
Some people seem to need a lot more light than others for their body to function normally.
And he went on to explain how the light box treatment works.
He said: "In the northern hemisphere, the body's testosterone production naturally declines from November through until April and then rises steadily through the spring and summer with a peak in October.
"You see the effect of this in reproductive rates, with the month of June showing the highest rate of conception. The use of the light box really mimics what nature does."
Prof Fagiolini said he thought the light therapy inhibited the pineal gland in the centre of the brain, which allowed more testosterone to be produced.
There are several possible reasons for lack of sexual desire and treatment depends on the underlying cause.
It can be treated with testosterone injections, antidepressants, and other medications.
The researchers believe that light therapy in the future may offer the benefits of medication, but with fewer side effects.
But he said they were not yet at the stage where they could recommend it as a clinical treatment.
The paper will be presented at the European College of Neuropsychopharmacology (ECNP) Congress in Vienna.