Case Studies

Why Ambient Light is Important in the Reading Room | EIZO

Controlling ambient lighting in reading rooms is vital to ensuring that radiologists are able to see scans and notice potential problems as optimally as possible. But why is it so important? Read on to learn the major reasons why ambient light is important, and how you can achieve the optimal reading room. 


01 Contrast

02 Eye Fatigue

03 How to Achieve Optimal Ambience








When viewing medical images, one of the most important factors for accurate diagnosis is contrast. The higher the contrast, the more differences in shades our eyes are able to see. Most medical monitors aim to provide high contrast screens, which is certainly the first and most important way to increase contrast. But even with a high contrast monitor, one little thing can greatly reduce contrast: ambient light.

Ambient light can reduce contrast in several ways. The most obvious ways would be:

  1. Diffuse Reflections: Light is reflected uniformly across the screen, whitewashing the blacks on screen.
  2. Specular reflections and glare: Light is reflected onto the screen directly from an external light source, or reflected off of an object, causing glare or a ‘specter’ of the object to appear on screen. This can be distracting and reduces the contrast at that specific location.

However these can be minimized by using anti-reflective coatings on the screen, and positioning the monitor in such a way that light does not directly reflect onto the screen.

The most major way that ambient light can reduce contrast is by affecting the eyes’ ability to adapt to a certain level of light. At any one time, the human eye can detect a contrast ratio of 1000, however this ratio is not definite, but rather relative. For example when in a dim tunnel you will be able to see most things clearly. When you suddenly exit into the sunshine outside, most objects will be brighter than the bright objects in the tunnel, so they will appear as a bright white to your vision. This is because in the dim tunnel, the darkest objects become ‘black’ to your perception, and the bright objects – for example the dim light coming the ceiling – become ‘white’ to your perception. Anything brighter than the dim light would automatically register as ‘white’ to your vision – thus when you step outside you will suddenly be blinded because the majority of objects will be brighter than anything in the tunnel.



Eyes adapt to the brightness level of one’s environment. If adapted to a dark tunnel, suddenly exiting will cause you to be momentarily blinded with white. However after several minutes the eyes will re-adapt to this brighter environment.


Conversely, if your eyes are adjusted to a sunny environment and you suddenly go into a dim tunnel, everything darker than the dark objects in the sunshine will suddenly appear black. You have probably experienced this yourself either entering or exiting a tunnel or dark room, and know that it takes several minutes until you can clearly see again in a new environment.

This is relevant in the reading room, because if the screen and the ambient light are quite different (either brighter or darker) your vision will constantly be readjusting between the ambient light and the screen each time you look away from the screen. Despite your eyes adjusting to the screen, as soon as you look away to a brightly lit wall, light or object – your eyes will begin readjusting to this change in contrast. So, when you look back to your screen you will no longer have optimal vision until several minutes have passed.

In general it is recommended that the ambient lighting matches the brightness of your screen – which is stated to be 20 to 40 lux when the screen is at a brightness of at least 350 cd/m2 (or 420 cd/m2 for mammography), as per the American College of Radiology guidelines. However the European guidelines for quality assurance in breast cancer screening diagnoses recommends 20 lux or less. One study1 has shown that ambient lighting below 7 lux is too dark, and over 100 lux is too bright, so regardless of which recommendation is followed – ambient light must not be too dark or too bright. Additionally, before beginning work, a radiologist should allow their eyes to adjust for about 15 minutes2 to bring their vision to the optimal level.



The ideal reading room should have an ambient lighting to match the monitor screen. 



Eye Fatigue


The quality of human vision is incredibly varied – depending on environmental factors as mentioned earlier, and also on physiological factors. Eye fatigue – apart from being uncomfortable – can also temporarily degrade one’s vision. Having optimal vision is vital in radiology, so it’s important to reduce any eye fatigue – and ambient light can have a large effect on this.

In a room where the ambient light is greatly different to the screen, every time you move your eyes from the screen to another location, your pupils will either dilate (if the ambient lighting is less) or contract (if the ambient light is greater). This constant dilation and contraction tires the muscles in your eye – leading to eye fatigue. This can also increase the amount of time that is needed for your eyes to adjust to a new setting.

Eye fatigue can also be caused by glare and reflections on the screen, which causes the eyes to refocus each time vision is passed over the brightened area.



Light can reflect onto the screen creating specters (left) and glare (right). 


A range of ergonomic issues can also cause eye fatigue. Read ‘How to Create the Ideal Ergonomic, Stress-Free and Work Efficient Environment’ to find out more. 



How to Achieve Optimal Ambience


Lighting behind the monitor prevents reflections and glare.


The best way to control ambient light is with dim lights that are positioned behind the screen. As overhead lights – even dimmed ones – can cause glare and reflections it is recommended to position lights behind the monitor.

However many radiologists may find that this environment is too dark to comfortably read papers and make notes. For this reason a small light positioned below or beside the monitor is ideal for illuminating papers and notes on the desk.

EIZO offers a device which can do all of the above. The RadiLight is a small light that attaches to the back of RadiForce monitors and gently illuminates the wall behind the monitor. This prevents any glare or reflections, and also illuminates the room to the ideal brightness. It also has an additional spot light on an adjustable arm which can be easily switched on and off with just the touch of a button, and moved to illuminate a specific area of your desk. It is made using non-reflective materials to ensure that light does not reflect onto the screen. The brightness of these two lights is also adjustable to ensure that the ultimate ambient lighting is achieved. 





Easily attachable light for RadiForce medical LCD monitors.

  • Gently illuminates the wall behind your monitor
  • Adjustable brightness
  • Flicker free
  • Spotlight for navigating the workspace
  • Easily attachable to RadiForce monitors



1. Mark McEntee, Patrick Brennan, Micheal Evanoff, Peter Phillps, William T. O Connor, David Manning, "Optimum ambient lighting conditions for the viewing of softcopy radiological images", Proc. SPIE 6146, Medical Imaging 2006: Image Perception, Observer Performance, and Technology Assessment, 61460W (17 March 2006); doi: 10.1117/12.660137;

2. George C. Kagadis, Alisa Walz-Flannigan, Elizabeth A. Krupinski, Paul G. Nagy, Konstantinos Katsanos, Athanasios Diamantopoulos, Steve G. Langer, “Medical Imaging Displays and Their Use in Image Interpretation”, RadioGraphics 2013, vol. 33, p. 275-290; doi: 10.1148/rg.331125096;