Hong Kong is one of the most densely populated cities in the world. Its buildings are largely high-rise blocks constructed close to each other and, hence outdoor obstructions play significant roles in daylighting designs. The light reflected from the ground and surrounding buildings can be important sources of interior lighting and detailed computations are required. We currently propose a calculation procedure in terms of a number of regression equations to determine the daylight illuminance on vertical surfaces. This paper presents the work to assess this approach via full-scale measurements under real sky conditions. The mean surface reflectance for external obstructions was estimated using lighting simulation techniques. It was shown that daylight illuminance obtained by the proposed method were in reasonably good agreement with measured readings. The simple nature of the proposed approach offers building professionals and students a reliable and convenient alternative to predict daylight illuminance particularly when different daylighting schemes and concepts are being considered.
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