Hospital Wayfinding Sign Legibility
A hospital outpatient department is replacing a suspended wayfinding sign above a corridor junction. The sign is viewed from up to 4.5 m along the corridor. It carries two lines: 'RADIOLOGY' and '放射科' (Radiology in Chinese). The existing sign is 900 mm wide by 300 mm high, with 25 mm cap-height white letters on a light grey background, an estimated luminance contrast of 2.1:1. The typeface is a condensed sans with tight spacing. The bottom of the sign is mounted at 2.25 m, but a ceiling service bulkhead at 2.40 m projects 450 mm into the corridor and hides the top 60 mm of the sign from a viewer 1.6 m tall standing 3 m away. The client wants to keep the 900 mm width and the same mounting height to avoid new supports. The designer must decide what to change and provide evidence for each change.
1. Using a minimum cap-height rule of 1 mm per 250 mm of viewing distance, check the 25 mm letters for the 4.5 m viewing distance. Explain why this rule alone is not enough for this sign and recommend a practical cap height.
Read the worked answer
At 4.5 m = 4500 mm, the rule gives 4500/250 = 18 mm minimum cap height. The existing 25 mm passes that numerical check, but the rule assumes high contrast and good acuity; at 2.1:1 the sign is well below the usual 4.5:1 minimum for normal text and below 3:1 for large text. Low contrast effectively reduces the usable viewing distance. Also, Chinese characters at 25 mm have dense strokes that fill in at distance, and the condensed face reduces letter differentiation. A practical cap height is 40–50 mm, with 45 mm as a reasonable target: it gives a 1:100 cap-height-to-distance ratio, roughly double the minimum, and leaves margin for the contrast deficit. Check the width: 'RADIOLOGY' in a normal-width sans at 45 mm cap height is about 9 × 27 mm = 243 mm plus spacing, so it fits the 900 mm width with room for the Chinese line and an arrow.
2. Evaluate the occlusion and mounting height. Determine whether lowering the sign would help or worsen visibility, and propose a mounting range with reasoning.
Read the worked answer
At 3 m from a 1.6 m eye height, the line of sight to the top of the sign rises 0.95 m over 3 m, an angle of about 17.6°. The bulkhead at 2.40 m projects 450 mm; its lower edge intercepts that line before the sign. Lowering the sign moves the whole panel down, so more of it falls below the bulkhead sightline, but the underside must stay above 2.0–2.1 m for head clearance and to avoid being blocked by people. A mounting range with the sign top at or below 2.35 m and the bottom at about 2.05 m would clear the 2.40 m bulkhead for the stated viewer while keeping the underside above 2.0 m. Keeping the same 2.25 m bottom is not defensible because the top 60 mm is hidden. If the bulkhead cannot be moved, lower the sign rather than enlarge it upward.
3. Recommend changes to contrast, type, and layout within the 900 mm width. Justify each with a measurable criterion.
Read the worked answer
Within 900 mm: (1) Change to dark text on a light background or white on a dark blue or green, targeting at least 4.5:1 contrast; measure with a luminance meter, not by eye. (2) Use a normal-width humanist sans, not condensed; set cap height at 45 mm for both English and Chinese, with Chinese characters not smaller than the Latin cap height. (3) Put 'RADIOLOGY / 放射科' on one line if it fits, or give the Chinese line at least 1.2× line spacing; add a left-pointing arrow at 60 mm. (4) Keep the 900 mm width but remove any non-essential border; the message area should dominate. (5) Check the sign at 4.5 m in the actual corridor light, including the bulkhead shadow. These changes are measurable: 45 mm cap height, at least 4.5:1 contrast, and no text above 2.35 m.