Seoul turns down billboard brightness across the city

SEOUL - As large outdoor LED billboards continue to proliferate across South Korea’s capital, the Seoul Metropolitan Government on March 31 announced the nation’s first comprehensive guidelines to curb excessive screen brightness.

The city said it has set new day-time brightness limits and adjusted night-time standards based on screen size and time of day.

The recommendations apply to displays measuring 30 sq m or larger and take effect on April 1.

The guidelines follow a survey of 52 major billboards across the city conducted between January and March. Using a reference display area of 225 sq m, the city categorised screens into medium (30 sq m to 225 sq m) and large (more than 225 sq m).

According to the survey, daytime brightness levels varied widely. Measured in candelas per square metre (cd) – a unit of luminous intensity – brightness ranged from 1,448cd to 14,000cd, with a median of about 7,000cd.

After comparing the findings with international standards and consulting industry experts, the city set the new day-time brightness recommendation at 7,000cd or lower.

Officials said the level is sufficient for outdoor visibility while curbing unnecessary glare.

Night-time measurements showed brightness levels ranging from 100cd to 1,500cd, with a median of about 400cd.

Under the new rules, medium-sized billboards must remain below 500cd from one hour after sunset until midnight, and 400cd after midnight. Large billboards must stay under 400cd until midnight and 350cd thereafter.

These adjustments lower the current legal ceiling of 1,500cd to as little as one third of the existing limit, a move aimed at reducing glare for pedestrians and improving nighttime road safety.

The guidelines also introduce measures to reduce visual fatigue from digital content. The city advises minimising high-brightness white backgrounds in static images, using lower-luminance colour schemes, and applying gradual transitions instead of abrupt brightness changes. Repetitive flashing and intense strobe effects should be avoided, it added.

City officials said the new standards are expected not only to improve the urban landscape and reduce discomfort but also to yield energy savings of about 15 per cent.

Analysis of the 52 surveyed billboards showed that reducing peak daytime brightness from about 10,000cd to below 7,000cd could significantly cut power consumption.

“This is not a blanket regulation but a targeted adjustment to curb excessive brightness,” said Mr Choi In-gyu, head of the city’s design policy division. “It balances advertising visibility with reduced visual strain for residents while improving energy efficiency.”

The recommendations come as large-format digital billboards become an increasingly prominent feature of Seoul’s landscape, particularly in areas such as COEX, Gwanghwamun Square and Myeong-dong, which have been designated as free advertising zones. THE KOREA HERALD/ASIA NEWS NETWORK