Illegibility

Illegibility is the condition of being difficult or impossible to read due to insufficient clarity of text. It focuses on the ability to decode letters, words, and symbols, and is distinct from readability, which concerns the ease of understanding the meaning after decoding. Illegibility impedes quick and accurate recognition.

Causes include visual factors (reduced acuity, glare, poor contrast, small or uneven letter size) and typography (thin strokes, cramped or irregular spacing, overly ornate or unfamiliar typefaces). Handwriting quality, especially dense cursive or poor penmanship, can also reduce legibility, as can display or print resolution and digital rendering.

Context and impact: illegible text hinders communication in education, workplaces, signage, and healthcare, and poses accessibility barriers for people with visual impairments or aging eyes. In safety-critical settings, unclear instructions or warnings can raise risk and error rates. Legibility improvements enhance speed of decoding and reduce cognitive load.

Assessment and standards: legibility is often evaluated by reading accuracy and speed under controlled conditions, along with objective factors such as contrast ratio, font size, and spacing. Design guidelines emphasize high contrast, sufficient size, clear typefaces, and ample white space to improve legibility.

Related terms: legibility describes the clarity of letter forms; readability concerns overall comprehension and flow of text. In practice, designers and publishers aim to maximize both by choosing legible typefaces, appropriate sizes, and accessible layouts, consistent with accessibility standards such as WCAG.