Studies have linked adverse health outcomes to work during the body's subjective night. Certain shift schedules result in light exposure profiles that may cause circadian disruption. Previous studies estimated average artificial illuminance to quantify light at night (LAN) at work which limits their validity and scope. However, daylight, shift length, commuting exposures and light during restricted sleep opportunities compete with LAN as causative agents, as do non-photic factors such as social disruption, activity and food intake during the subjective night.Investigations into the effects of light in shift work should be supported by 24-hour light exposure measurements, e.g. to establish dose-response relationships. The purpose of the study was to collect and suggest interpretations of 24-hour exposure data, and investigate both daytime and night-time workers' light cycles in more detail.

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Shift work causes disruption to circadian physiological processes in the human body, and desynchronization from the natural day-and-night rhythm. Circadian disruption is thought to explain the associations between shift work and various long-term diseases; light is an unrivalled synchronizer (or Zeitgeber) of circadian processes and inappropriate light exposure plausibly plays a critical role in the development of health impairments. As published measurement data on the actual light environments encountered by shift workers are sparse, nurses working in two hospitals in London (UK) and Dortmund (Germany) wore light-logging dosimetry devices to measure personal light exposures continuously over a week in three different seasons. The study identifies and quantifies several of the characteristics of light exposure related to different working patterns in winter, spring, and summer, and quantifies interindividual variations. These data enable informed design of light exposure interventions or changes to shifts to reduce unwanted effects of disruptive light exposure profiles.

Light emitting diodes (LEDs) are increasingly being used for general lighting in offices and play an important role in a growing number of other applications -for instance in electronic devices as computers, laptops or smartphones. It is sometimes claimed that LEDs would be more dangerous in terms of photochemical damage to the retina (known as the blue-light hazard) than conventional light sources.The paper presents results of blue-light hazard assessment of an LED, incandescent, halogen and compact fluorescent lamps, as well as displays of laptops and smartphones following the requirements of the Standard IEC/EN 62471 "Photobiological safety of lamps and lamp systems". It shows that in terms of their level of photobiological safety, LED lamps for general lighting are not different from conventional lamps and can be considered safe under reasonably foreseeable conditions of use. Laptop and smartphone displays pose no risk concerning the blue-light hazard.