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An experiment was conducted to evaluate intellectual productivity in three lighting conditions: (a) conventional ambient lighting, (b) task ambient lighting with normal colour temperature (5000 K) and (c) task ambient lighting with high colour temperature (6200 K). In the experiment, cognitive tasks were given to 24 participants. The concentration time ratio, which is a quantitative and objective evaluation index of the degree of concentration, was measured. The results showed that the average concentration time ratio under the task ambient lighting with high colour temperature was 72.5%, which was 5.0% points higher than that under the conventional ambient lighting. It is believed that intellectual work can be performed better when the concentration time ratio is high.

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For optimizing the balance between intellectual productivity and energy use in office buildings, we should reveal the mechanism of intellectual productivity variation of office workers. For this purpose, the authors had proposed an intellectual productivity model. The model is a state transit model based on short pauses while working. This model can explain the productivity variation of most of subject experiment results. In some cases, however, the explanation is insufficient with previous 2-state transit model. In this study, the authors have proposed an improved model assuming 3 states. A subject experiment was conducted where illuminance on the desk and work motivation were controlled to vary their productivity. The experimental result was emulated with 2-state/3-state transition models and their accuracies were compared. As a result it was confirmed that the 3-state model simulated more accurately. It means the 3-state transition model can explain productivity variation better than the 2-state transition model.