Therapeutic daylight for hospital patients: a search for the benchmarks

To evaluate the therapeutic potential of daylit in-patient rooms, it is important to know the characteristics of daylight objectively (e.g. intensity and duration) which might support patient health effectively and are merely different from lighting requirements for visual purposes, such as viewing objects and doing work or movement. In the absence of a suitable standard, the upper and lower limits of daylight recommended by previous researchers to support patient health and comfort were selected for verification as the benchmarks of therapeutic daylight for hospital patients. Therapeutic daylight was defined as the level of daylight that can support patients to recover quickly. A field survey was conducted to collect real-world patient data from an existing hospital building. Clinical and demographic information were collected from hospital records. The amount of daylight that a particular patient might experience on the head during his/her stay in the bed was estimated by calculating the average ratio between two indoor data loggers: one installed at the back wall of patient bed (head side) and the other kept on vacant beds at the location of patient head. Based on the amount of daylight experienced, the sample patients were grouped under three categories and their post operative length of stay (LoS) inside in-patient rooms were compared using Multiple Linear Regression (MLR) analysis. The coefficient estimates of the developed MLR model (adjusted R square = 0.516, F = 40.931 (Sig. < 0.001)) shows that while holding the other explanatory variables constant (provision of outdoor view, rent of the rooms, mean arterial pressure, heart rate and diabetes mellitus), being in lower daylight group (below 190 lx) adds 42 hours (t=3.096, P value=0.002), and being in higher daylight group (above 2000 lx) adds 29 hours (t=2.094, P value<0.037) in patient post operative LoS in hospital rooms with respect to the group experienced the moderate levels of daylight (between 190 – 2000 lx). It was concluded that the range of 190 – 2000 lx can be regarded as effective daylight intensities within which positive health outcomes are more likely to occur, and architects could use this benchmark for therapeutic daylighting design.