Understanding how human vision adapts to different light levels

A chapter authored by Professor John Barbur and colleagues on human vision across different light levels, which originally featured in the Encyclopaedia of the Eye (2nd edition), has been selected for publication as a stand-alone chapter in the prestigious Reference Collection in Neuroscience and Biobehavioural Psychology.

Professor Barbur, who is Professor of Optics & Visual Science at City St George’s, University of London, is a leading expert in the field of colour and mesopic vision. The accolade highlights the importance of vision research, and the chapter explains new insights into how our vision changes with increasing age and how the eye adapts across a wide range of illumination, from dim starlight to bright sunlight.

Human vision

Originally written by Professor Barbur and colleagues from City St George’s and the UCL Institute of Ophthalmology, the chapter addresses the challenges posed by the dynamic range of light the human visual system encounters daily. It reveals that effective vision is a compromise between sensitivity to light and ability to see fine detail, where the eye's rods and cones (cells responsible for light detection) collaborate at different light levels to optimise visual performance.

A key revelation is the complexity of mesopic vision—the intermediate light range—where both rods and cones contribute to vision. This zone is particularly crucial in many occupational environments and daily tasks conducted under low lighting, such as driving at dusk. The authors emphasise that current models of luminous efficiency, which measure how different light sources affect vision, are inadequate for capturing the full range of visual performance, particularly under mesopic conditions.

The research also highlights how spatial and temporal acuity, colour perception, and contrast sensitivity are significantly affected by light levels. For instance, at lower light levels, rod signals dominate, leading to poor colour vision and reduced spatial acuity. The findings also reveal that visual performance deteriorates with age, more so under mesopic conditions, where older individuals struggle much more with spatial vision and colour perception when compared against younger individuals.

Practical implications

Besides providing valuable insights for vision science, the research contained within the chapter also has practical implications for lighting design in workspaces and urban environments, where enhancing visibility under varying light conditions is critical for safety and productivity.

As the science of vision continues to evolve, these findings represent a significant step toward understanding how we can optimise lighting conditions to maintain visual performance in critical settings such as driving, aviation, and medical environments.

Commenting on the significance of this recognition, Professor Barbur said:

It is an honour and a great surprise to have this chapter selected for publication in such a prestigious collection. Important aspects of human vision, and how it varies at different light levels, are often overlooked, yet they are critical for many real-world tasks. Our research not only advances the scientific understanding of how the visual system adapts to different light levels, but also offers practical implications for improving safety and performance in challenging visual environments and a better understanding of how to cope with vision changes with increasing age.  

I hope the chapter will also serve as a useful resource for future studies exploring how human vision operates across a wide range of light levels, and how this knowledge can be applied to improve human performance and safety.