The month of February can sometimes bring about dour moods for those who find themselves single around Valentine’s Day. Not only that, holiday happiness has well worn off, and the dead-middle-of-winter weather can be quite dull too. The traditional cure for the winter doldrums has been bright lights to lighten dark moods, but new research from Johns Hopkins University found that too much light might actually have the opposite effect.

The study, published in the journal Nature, exposed mice to three-and-a-half-hours of light followed by three-and-a-half hours of darkness for two weeks. They had increased levels of the stress hormone cortisol and displayed signs of depression, like moving less, taking less pleasure in fun activities and showing less interest in new objects. They also suffered learning deficits.

Though the study needs to be tested on humans, the science behind it is based on what mice and men have in common: Photoreceptors in our eyes pick up light signals and activate the brain’s limbic system, which controls memory and emotion. At night, it’s supposed to rest, but bright light charges it up again.

The research backs up previous studies that have shown how bright light from electronic devices like T-Vs, cell phones and laptops can disrupt sleep cycles by decreasing melatonin levels. It could even increase the risk of heart disease, obesity and cancer.

So what if you’re a shift worker and can’t block out the light? Scientists suggest dimming overhead lights and computer screens. Get more light during the day and shut it out at night. Unplug electronics to minimize light pollution. Regulating your sleep cycle to sync with daylight hours can get your brain and body more in tune and feeling better in February and the months to follow.