Did you know that pure black text can cause eye strain? A survey found that “58 percent of adults in the U.S.” have experienced eye strain from working on computers. Designers can do their part to reduce the likelihood of eye strain on their designs by paying attention to the color of black they use.
Pure Black Text on White Backgrounds
Pure black text on white backgrounds can cause eye strain when users read the text over an extended period. White has 100% color brightness, and black has 0% color brightness. Such a disparity in color brightness creates intense light levels that overstimulate the eyes when reading text. This causes the eyes to work harder to adapt to the brightness.
An example that illustrates this concept is when we turn on a bright light in a dark room. Such a drastic change in light conditions is harsh to our eyes. But if we turn on a dim light in a dark room, our eyes adapt to the change easier because our retina isn’t overstimulated by such a sharp increase in contrast.
Instead of black text, use dark gray text on a white background, so the change in brightness isn’t as drastic. This prevents overstimulating the retina and allows users to read for a more extended period.
A research study found that “black text on a white background overstimulates the OFF ganglion cells while white text on black background overstimulates the ON ganglion cells.” This finding means that “white text from a black screen could inhibit myopia, while black text on white background may stimulate myopia.” The study advises against reading black text on a white background due to the striking effects of contrast polarity.
White Text on Pure Black Backgrounds
There’s also reasons why you shouldn’t use a pure black background with white text. A pure black background kills all light emitting from the screen. This makes eyes work harder and open wider since it needs to absorb more light. When this occurs, the white letters can bleed into the black background and cause the text to blur. This effect is known as “halation” and it affects users with astigmatism, which people of all ages could have.
Instead of a black background, use a dark gray background so that more light emits from it and the text doesn’t bleed. Doing this decreases eye strain and strengthens reading stamina.
High Contrast for Accessibility
Pure black isn’t harmful to all users. Low vision users, who are sight impaired but not blind, tend to read text better with pure black text or white text on a black background. When designing for them, you may need to use black for an accessibility mode. For normal-sighted users, stick with dark gray over black to prevent eye strain.
Balanced Contrast for Better Readability
High color contrast is useful for readability. Too high of color contrast, however, creates a significant disparity in light levels that affect the user’s eyes when they read. A balance of contrast between the text and the background color is an effective way to make your text safe for the user’s eyes.
If you’re unsure about your color contrast, you can use a color contrast checker to find an optimal range that works for you. It shows you when your color contrast is too low based on accessibility guidelines. However, it doesn’t indicate when your color contrast is too high. That decision is left for the designer’s careful eye to decide.
Text color isn’t limited to black and white, but it’s the most common color combination for text. Before designers use it, they need to think about how it affects the user’s eyes. Designing to reduce the pain of eye strain means users can spend more time reading and enjoying the content on your interface.