Dark Mode vs Light Mode for Medical Device UIs

By Oliver Cook 

User interface (UI) design plays a crucial role in the overall user experience of a product and is especially important when used to convey critical information in products such as medical devices. One of the recent ongoing debates in UI design is light vs dark modes. 

What is dark mode vs light mode? 

• Dark mode (negative contrast polarity) is characterized by light text on a dark background, which reduces the overall light emitted by the device screen. 

• Light mode (positive contrast polarity) is characterized by dark font text on a light background, which increases the overall light emitted by the screen. 

Dark mode vs light mode – which is better? 

While both have their merits, correctly implementing them is essential for ensuring readability and usability in medical devices.  

Readability 

Readability is important in medical devices where accurate information and quick decision making is vital. Light UIs often have better legibility, making text and graphical elements stand out clearly against the background. Black text on a white background is the classic example of high readability. However, extended exposure to bright screens can cause eye strain and discomfort, particularly in low light environments. The blue light emitted by most display types can also cause sleeping problems; this is why blue light glasses for computer work have become so popular in recent years.   

On the other hand, dark UIs, such as white text on a dark background, can be visually appealing and can reduce eye strain in dimly lit environments. However, poor contrast ratios between text and backgrounds can hamper readability, which could lead to misinterpretation or use-errors.  

Usability 

Usability is a critical aspect of UI design, particularly in medical devices that require swift and precise interactions. A user-friendly interface can significantly impact patient care and outcomes, particularly with software as a medical device (SaMD) devices where the user interacts with the entirety of the device through the UI. 

Light UIs are generally considered more intuitive and familiar to users due to their resemblance to traditional paper documents. Elderly users, especially those not following the latest digital trends with UI design, may find it easier to navigate a light themed UI.  

Dark UI, when appropriately implemented, can be equally usable. However, designers must pay special attention to color choices, iconography, and ensuring clear visual hierarchy to prevent confusion and enhance the overall user experience.  

Use environments  

Medical devices are used in a wide multitude of environments, from brightly lit operating rooms to dimly lit patient rooms. The choice of UI theme should be adaptive to these conditions.  

Consider the times of day the device will often be used. A bedside monitor may need to be checked through the night, so a darker UI may be more suitable so as not to disturb the patient. A well-lit operating room may be better suited to a light UI where information clarity is vital. However, if the operating room is dark, the emission of white light may be harsh, especially during prolonged surgeries. By using dark mode, the contrast is reduced, potentially mitigating eye strain.  

User groups 

An important factor to consider is who will be using the device. It would be a reasonable assumption that some users of the UI may suffer from some form of visual impairment. Therefore, this may impact the decision of which theme to implement. Users with cataracts may prefer a dark UI as there is less light to be scattered abnormally due to their cloudy ocular media; although the UI is darker, it is clearer for these users to see the contents of the screen. However, if the user groups have not been clearly defined, giving the option of both provides flexibility to meet the preferences and needs of the user. 

Summary: Dark vs light mode for medical device UIs 

Medical devices by nature demand a high level of precision, accuracy, and reliability. UI design should complement these requirements rather than hinder them. In critical situations, both light and dark UIs have their roles to play. For instance, during surgical procedures, a light UI might be preferable for optimal visibility, while a dark UI could be more suitable for continuous monitoring in a patient’s room during the night. One of the key points to consider is to prioritize safety and usability above all else. Incorporating features like adjustable screen brightness and contrast settings can further empower users to tailor their UI to their specific needs and working conditions. 

In conclusion, the UI design consultants from Emergo by UL say the debate between light and dark UI design should be approached pragmatically in the context of medical devices. Readability, usability, and user-centered design should be at the forefront of decision-making.  

Oliver Cook is a senior interface designer for Emergo by UL.