Measuring Light-Switching Behavior Using an Occupancy and Light Data Logger

Summary

This article describes a procedure for using and deploying an occupancy and light data logger which allows collecting data about light-switching behavior of participants in field settings.

Abstract

Due to discrepancies between self-reported and observed pro-environmental behavior, researchers suggest the use of more direct measures of behavior. Although direct behavioral observation may increase the external validity and generalizability of a study, it may be time-consuming and be subject to experimenter or observer bias. To address these issues, the use of data loggers as an alternative to natural observation can allow researchers to conduct broad studies without interrupting the participants' naturally occurring behaviors. This article describes one of such tools—the occupancy and light data logger—with its technical description, deployment protocol, and information about its possible applications in psychological experiments. The results of testing the reliability of the logger in comparison to human observation is provided alongside an example of the gathered data during a 15-day measurement in public restroom (N = 1,148) that includes: 1) room occupancy changes; 2) indoor light changes; and 3) room occupancy time.

Introduction

One of the most commonly used measures of pro-environmental behavior in psychology are self-reports in the form of surveys, interviews, or questionnaires¹. Among the reasons indicated for this trend is simply the difficulty in conducting field experiments, which usually require a fair amount of resources and precise operationalization^2,3. However, the tradeoff is worth the effort since it is well established that relying on self-reporting measures can be misleading in the prediction of objective behavior^4,5,6.

While trying to avoid this problem, researchers that are focused on studying energy conservation behavior generally use observational (nominal categorization of observed events, e.g., turning on/off lights) or residual (quantifiable evidence of a past behavior, e.g., energy consumption in kWh) data as measurements of dependent variables⁷. Although both types of measurements are valuable, observational data is most commonly used in field experiments^2,3,8, particularly when their dependent variables concern light-switching behavior.

Before obtaining observational data, researchers should consider several methodological issues, which are: 1) sample representativeness; 2) the number of observers in order to exclude possible human errors; 3) inter-observer agreement in order to exclude experimenter bias; 4) observer location, which should be concealed in order to reduce the possibility of being spotted by participants; 5) clearly and specifically defined observation coding; 6) pretest of observational measures; 7) observer training; and 8) establishing systematic timing of observation⁹. Even though most of the mentioned issues were already addressed—for example those that concern reliability analysis¹⁰ or coding observational data¹¹—it seems that not all of them receive much attention in articles that describe experiments on light-switching behavior.

An analysis of four studies^12,13,14,15 that were chosen for their similarity in experimental context (all of them concerned light-switching behavior in public bathrooms/restrooms) showed that even though the location details in each of the studies were precise, the observation measurement details varied. Since each study employed naturalistic observation, gathering information about the behavior of participants that were the opposite sex of observers was not always possible¹⁴ due to possible interference or violation of social norms (e.g., if a male experimenter were to enter a women's restroom or vice versa). In some instances, the precise data of the participants' genders were not provided¹⁵. This seems to be a limitation when taking into consideration that gender can be an important factor in predicting pro-environmental behavior¹⁶.

The biggest differences, however, emerged in the description of observers and measurement times. Even though these descriptions will naturally differ on the basis of experimental location, the precise number of observers was not always provided¹⁴. Furthermore, the exact location of observers was not explicit^12,14,15 which makes it hard to conduct possible replications and ensure that participants are unaware of being observed. Across four analyzed articles, only one provided a detailed description of the observer's location¹³.

Moreover, the exact times of observation intervals were provided only by one study¹² whereas other studies either described overall study times (with a general description of how many times on each study day the observation took place)^13,15 or did not describe it at all¹⁴. This can again impede replicating and establishing whether the observation timing was systematic and sufficient for the purposes of the study aims.

The limitations of these experiments are presented as guidelines and important points that should be taken into consideration in future research. In no case it was intended to undermine the importance of these studies. The indicated areas should be considered for maximizing study operationalization in order to facilitate replications, which play an important role in psychology^17,18, and simplify the conduction of field experiments. However, it is questionable whether all of the mentioned issues can be dealt with by improving observation methods that ultimately rely on human observers.

For these reasons, the occupancy and light data logger (see Table of Materials) is a valuable tool that can be effectively used to gather information about a particular type of energy conservation behaviors, light-switching, without the limitations of using observers or ethical restrictions (the logger does not gather the audio-visual data). Overall, the aim of this article is to present the technical description and possibilities of one model of the occupancy and light data logger. To the authors' knowledge, this is the first attempt to present this tool thoroughly in the context of its use in field experiments in psychology.

Loggers' technical description
The model of occupancy/light data logger (see Table of Materials) that was used for this article was equipped with standard memory capacity of 128 kB. The logger weights 30 g and its size is 3.66 cm × 8.48 cm × 2.36 cm. Additional details and the product manual can be found on the manufacturer's website¹⁹.

Control buttons, the light sensor and the battery tray are located on the top panel. The front panel consists of the occupancy sensor and an LCD screen, whereas the back panel is equipped with mounting magnets and loops (Figure 1). The USB 2.0 port is located on the bottom panel, to allow the connection of the logger to the computer with a USB cable in order to enable set-up before deployment and to later obtain readouts using analysis software package dedicated to this data logger.

The integrated light sensor (photocell) threshold is greater than 65 lx, which works with different light types (LED, CFL, fluorescent, HID, incandescent, natural) that can be found in most public spaces. Overall, the logger interprets light status changes (ON/OFF) depending on the strength of the light signal, more precisely, whether it drops below or rises above levels of the calibration threshold. It should also be noted that the sensor is secured from false detection of ON and OFF states by a built-in hysteresis level of approximately ±12.5%¹⁹.

A motion sensor determines whether the room is occupied or unoccupied. With the use of a pyroelectric infrared (PIR) sensor, it detects the motion of people by their body temperature (which differs from the temperature of the surroundings). The detection range of the discussed logger has a maximum of 5 m and the extended version of the logger has a range of 12 m. Horizontal detection performance works up to 94° (±47°), and vertical up to 82° (±41°).

The described model of occupancy/light data logger has been validated alongside Open Source Building Science Sensors and appears to provide a reliable measurement of light intensity and occupancy frequency²¹. Furthermore, these models of loggers have been shown useful in built-environment research, precisely in lighting applications^22,23,24.

Protocol

The study was approved by the ethics committee of the SWPS University of Social Science and Humanities in Warsaw (number 46/2016).

1. Choosing an experimental site for logger deployment

1. Choose an indoor experimental site that will allow mounting the logger in close proximity to the light source (for adequate light changes detection) as well as to gather the data on the behavior regarding the room occupancy status (for adequate movement detection) of individual participants (i.e., one at a time).
2. Establish the intended use of the room and its designated users (males, females or co-ed).
   NOTE: An example of an experimental site could be a public single-stall restroom due to the fact that this type of room is frequently and individually visited by its users. Furthermore, in most instances, it is possible to specify if the room is visited by males or females, based on its designation.
3. Visit a chosen site and note the type / number of functioning light sources along with their light switches. Check whether multiple light sources are controlled by one or multiple light switches.
4. Check the possibilities of mounting the logger next to the light source. Ensure that the place of logger mounting is not in proximity to any kind of heating sources (e.g., heaters, windows or mirrors) to ensure that only the body heat of the room users will be recorded.
5. Acquire any necessary written permissions from the site owner for installation of the logger and conducting the experiment. Provide the site owner with the details of the experiment, loggers' type and its application in written form.

2. Logger configuration before deployment

1. Download and install the dedicated software (see Table of Materials) available for Windows/Mac platforms for launching, reading out, and plotting data from data loggers.
   NOTE: Additionally a detailed description with basic system requirements and the software manual can be found on the manufacturer's website (see Table of Materials).
2. Connect the logger via USB cable to the computer (plug the larger end of the USB interface cable into a USB port on the computer and the smaller end of the USB interface cable into the port on the device).
3. Launch the software.
4. Click the Launch icon on the toolbar (or select Launch command from the device menu) which opens loggers' setup window.
   NOTE: This option will be unavailable when the logger is not connected to the computer. The Launch Logger window is divided into the following three sections: 1) logger Information which presents model, serial number, deployment number, and current battery level of the selected logger; 2) list of the sensors available for the logger; and 3) deployment configuration. From this interface, one can set specific features that will configure the logger before deployment, such as those previously mentioned: sensor configuration, configuration of data display filters, start/stop logging, and display of the LCD screen.
5. Enter a name for the launch which will be used as the default file name during read out and saving the data recorded by the logger.
6. Select the Light sensor. Set the measurement to log State from the drop-down list, and choose the state description off/on from the drop-down list.
7. Select the Occupancy sensor. Set the measurement to log State from the drop-down list, and choose the state description unoccupied/occupied from the drop-down list.
   NOTE: Occupancy and light sensor channels can be configured to log state changes or runtime. On the state change setting, the work of the logger is event-dependent. While checking every second for a state change, the logger will only record a time-stamped value (how long an event lasts, date and time) when the state change occurs. On the other hand, on the runtime configuration setting, the logger checks and records the state of the sensor status once every second.
8. Click the Filters button to enable automatic calculation of additional values (e.g., maximum, minimum, average, or total).
   NOTE: Step 2.8 is optional and serves for filtering data for each series during loggers' readout.
   1. Select the sensor type of choice. Select the type of filter and the interval to use.
   2. Edit the Name and click Create New Series. Click Done.
9. Click the Advanced button to access the sensor properties.
   1. Select the Light sensor. Select Set to maximum sensitivity for calibration and click the Save button.
      NOTE: By default, the light sensor can be auto-calibrated at the location where the logger will be deployed using the control button located on the top panel. By simply pressing the calibration button, while on the site of deployment, the loggers' LCD screen will display the signal strength of the light being monitored (use this option when light levels in the experimental site are unknown prior to deployment). The sensors' sensitivity can also be adjusted via option "Set to Maximum/Minimum Sensitivity" - if the light levels in the place of deployment are known in advance. These forms of calibration ensure an accurate readout of light changes between ON and OFF states.
   2. Select the Occupancy sensor. Select a preset timeout value (i.e., 10 s; 30 s; 1 min; 2 min; 5 min) or select Custom and enter a value in minutes and seconds if needed. Click the Save button.
      NOTE: The timeout value specifies the period of inactivity required for the sensor to consider the area unoccupied. By default, this attribute is set to 1 min.
10. Select when to launch the logger, depending on the experimental plan: 1) immediately; 2) at intervals (available when logging runtime); 3) on a specified date/time; or 4) by manually using the start button.
11. Select when logger should stop logging: 1) when memory fills; 2) stop at a specified date/time; 3) stop manually or 4) never stop—resulting in the newest data overwriting the oldest.
12. Click the Start button upon finishing the configuration. Unplug the logger from the computer.

3. Deploying the logger in the field settings

1. Visit the experimental site before the time the logger will start recording the data.
2. Equip the logger with an additional fiber optic light pipe (see Table of Materials) by connecting it to the back of the logger, in order to filter out any ambient light (coming from windows or mirror reflections) and ensure the most accurate readings.
   NOTE: The light pipe is 30.48 cm long and can be bent to gain access to hard-to-reach areas, which can be also useful in hiding the logger from the sight of any room user.
3. Mount the logger with the light pipe next to the designated light source with the use of: 1) four built-in magnets on the back of the logger that can attach it to a magnetic surface; 2) adhesive strip that can be attached to the back of the logger to mount it on walls or other flat surfaces; 3) any double-sided tape to stick the logger to a surface; or 4) the hook-and-loop strap which can be used through the mounting loops on both sides of the logger to mount it to a curved surface.
   NOTE: The choice of the mounting method depends on the type of surface to which the logger will be mounted.
4. Leave the experimental site for the time of data logging set or planned.
5. After finishing recording, revisit the experimental site and remove the logger for the purpose of data readout.

4. Data readout

1. Connect the logger via USB cable to the computer and launch the analysis software package dedicated to the data logger (see Table of Materials).
2. Click the Readout device button from the control panel or select Readout from the device menu, which will enable the logger to unload the gathered data.
3. Choose a location and a filename or accept the default location and name to save the data. Click Save and select the sensors and/or events to display in a graph and click Plot.
4. Select the series to view on the table data and plot. Click the All or None button to select or deselect all series, or click the checkboxes to select or deselect individual series.
   NOTE: The table data is presented numerically using added filters that were set before the deployment. Each column corresponds to the type of data gathered. For example, the column labeled "light" presents the occurrences of light-switching, whereas the column labeled "occupancy" presents the information about the presence of movement in the field where the logger was deployed. In each column, the state changes are presented dichotomously (the number "0" represents the light status of off in the "light" column and a lack of movement in the "occupancy" column).
5. Select Export table data from the control panel. Choose destination folder for the export.
   NOTE: It is possible to perform a data readout and export it to text, comma-separated values, or spreadsheet files. Other options, such as data plotting, are also available; however, due to the fact that most researchers work on exported data and use statistical packages, we decided to present the most basic data readout. For more information refer to the loggers manual¹⁹.

Results

Loggers' reliability test in comparison to human observation
In order to test the reliability of the logger in comparison to human observation, a 4 h field test was conducted in a single-stall male restroom located on the University campus. Two male observers waited outside the restroom (approximately 5 m away from the front door) and independently recorded the visitors' behavior in terms of occupancy rates/times and light switching (lights left ON or OFF upon exiting). Simultaneously, two ...

Discussion

When planning to use more than one site (for logger deployment) at the same time, it should be ensured that each site has an identical architectural layout in order to exclude the possibility of occurrence of different behavioral patterns from participants (i.e., resulting from occupancy times and light-switching possibilities). A suitable site should be equipped with one or more light sources with only one corresponding light switch, visible to the occupant. If otherwise, one should plann to use one logger fir each ligh...

Materials

Name	Company	Catalog Number	Comments
HOBO Occupancy/Light (5m Range) Data Logger	ONSET	UX90-005	As advertised by Onset - The HOBO UX90-005 Room Occupancy/Light Data Logger is available in a standard 128 KB memory model (UX90-005) capable of 84,650 measurements and an expanded 512KB memory version (UX90-005M) capable of over 346,795 measurements. For details and other products visit: https://www.onsetcomp.com/products/data-loggers/ux90-005
HOBO Light Pipe	ONSET	UX90-LIGHT-PIPE-1	An optional fiber optic attachment or light pipe that eliminates effects of ambient light to ensure the most accurate readings. For details visit: https://www.onsetcomp.com/support/manuals/17522-using-ux90-light-pipe-1
HOBOware	ONSET	-	Setup, graphing and analysis software for Windows and Mac. There are two versions of HOBOware: HOBOware (available for free) and HOBOware Pro (paid version which allows for additional analysis with different loggers). Each of them are dedicated to HOBO loggers. For details visit: https://www.onsetcomp.com/products/software/hoboware