This film looks at the essential role light plays in regulating our internal body clocks and why your daily dose of sunlight is so important.

In recent years the medical community has discovered that people who are blind or visually impaired can still use their eyes to detect the overall amount of light in their environment. This enables them to regulate their internal body clocks in the same way as everybody else.

For people who actually have no physical eyes, however, this ability to maintain a regular sleep–wake cycle can be severely compromised. These findings have brought into question the validity of medical operations to remove people’s eyes, a procedure that is sometimes performed for cosmetic reasons.

In this film we meet Meredith Plumb, who had her eyes removed after she gradually went blind following a chemistry accident.

“I don’t sleep normally and I don’t feel normal. I do feel that I live in a bit of a separate universe from everybody else,” says Plumb, who adds that she sleeps in 90-minute and 3-hour cycles throughout the 24-hour day. Plumb has embraced her situation by becoming a person-centred counsellor who offers advice without prejudice.

One pioneering research group in this field is the Sleep and Circadian Neuroscience Institute (SCNi) at the University of Oxford in the UK, led by Russell Foster. Foster’s group has identified that one in a hundred so-called ganglion cells in the eye are directly sensitive to light. Remarkably, the performance of these cells is unaffected by damage to the rod and cone cells of the visual system.

Foster and his group are developing an understanding of what genes are turned on and off as a result of light hitting the molecular clockwork of the eye. This information could be used to develop pharmacological mimics of light that could help people who have had their eyes removed to establish more regular sleep patterns.

The film is produced by London-based filmmaker Thom Hoffman, who has recorded interviews with Plumb and Foster, and combined them with stunning visual imagery to illustrate the interconnected nature of light and life. It is the second in a series commissioned by Physics World as an official media partner for the International Year of Light (IYL 2015). These short documentaries tell personal stories relating to some of the core themes of IYL 2015, the campaign for dark skies and the study after sunset initiative.

If you want to find out more about how light interacts with the eye, then check out the March issue of Physics World. This special issue devoted to light includes a special feature about how humans’ secret superpower: the ability to see polarized light.

• If you’re a member of the Institute of Physics (IOP), you can get immediate access to the special issue about light in our lives with the digital edition of the magazine on your desktop via MyIOP.org or on any iOS or Android smartphone or tablet via the Physics World app, available from the App Store and Google Play. If you’re not yet in the IOP, you can join as an IOPimember for just £15, €20 or $25 a year to get full digital access to Physics World.