3.1. Occupant satisfaction assessment method

The objective of this study was not the development or the validation of a complex assessment method for occupant satisfaction in office buildings, but rather the identification of weak spots within the described ADS at the LESO-SEB and the discussion of possible ways to deal with these weak spots. We have therefore decided to first roughly check occupant satisfaction with different aspects of their office lighting using a simple questionnaire. As there were only 29 persons working within the building at the time of the study (May and June 2007), the questionnaire had to be easy to understand and quick to fill out in order to maximize the number of returned questionnaires. A simple and reliable questionnaire-based assessment method for occupant satisfaction with office lighting is the Office Lighting Survey (OLS) presented by Eklund and Boyce in 1996 [8]. Many questions within the OLS only allow an answer on a symmetrical, two — stage Yes/No scale. Akashi and Boyce as well as Ramasoot and Fotios have used slightly modified versions of the OLS in 2006 and 2007, respectively [9, 10]. We have adapted the OLS to our specific situation within the LESO solar experimental building and have set up a questionnaire with 12 general, 9 daylighting-specific and 7 artificial lighting-specific statements. Occupants were asked to rate their agreement with each statement on a symmetric answering scale (i. e. without neutral choice) in order to avoid interpretation problems associated with possible neutral choices.

In order to make the questionnaire more sensitive, we have used a four-stage answering scale rather than the two-stage answering scale used within the original OLS. This means that for each statement, occupants had the possibility to answer “yes”, “rather yes”, “rather no” or “no”. These four possible choices were assumed to correspond to 100%, 75%, 25% and 0% of agreement with the respective statement. This fact can be described by

Rx n є {0,0.25,0.75,1} (1)

where Rx, n stands for the respective answer to question x by occupant n.

Furthermore, we had to define an optimal answer Rx, opt for each statement. In some cases, this optimal answer would correspond to 100% of agreement (e. g. when the occupant has to rate his agreement with the statement “In general, the lighting in my office is comfortable.”). In other

cases, the optimal answer Rx, opt would correspond to 0% of agreement (e. g. when the occupant has to rate his agreement with the statement “My office often seems too bright.”). We can therefore write

Ko, є {0,1} (2) where the appropriate value for Rx, opt has to be chosen by the experimenter for each statement.

In our questionnaire, every single statement was associated with one common problem often experienced in office lighting environments (e. g. glare problems, “not enough light”-situations, missing windows, etc.). As previously mentioned, the objective of this study was to identify the weak spots of the ADS installed within the LESO-SEB. In other words, we wanted to find out which of the commonly experienced office lighting problems were the most annoying to LESO — SEB occupants. In order to quantify the specific annoyance of each of these problems within the building, we defined a mean annoyance value (MAV) for each of our statements. The MAV can be computed as follows:

n=1

where x stands for the number of the respective statement and N stands for the number of persons who have returned the questionnaire. The parameter MAV is used in the following for quantifying the extent to which a certain lighting related problem applies to the LESO-SEB. The lower the MAV, the less annoying is the corresponding problem. Another parameter used in the following is the number of occupants directly concerned by a certain problem nconcerned. A person is considered to be directly concerned when he or she has replied opposite to the optimal answer Rx, opt to a certain question (e. g. “yes” or “rather yes” when the optimal answer is “no”).

The evaluation of the questionnaires made it possible to identify the main lighting related problems that are annoying to the LESO-SEB occupants. In order to find out which weak spots within the ADS are causing these problems to them, specific complementary interviews have been conducted with some occupants.