# Smartphones as a Light Measurement Tool: Case of Study
## 5 Results and Hypothesis Validation
### Hypothesis Validation  
Regarding the proposed hypotheses, they can be answered based on the research performed.  
The first hypothesis (H1) stated that the ambient light sensor that is present in most mobile devices provides enough quality to be used as a measurement tool, with the developed Android application and the measurements performed twice, one with the mobile phone and another with a calibrated luxmeter. Once all of the data were obtained and compared, it was possible to check how the accuracy of the light meter was too low, with an error of 39.08%. However, after a process of calibration, this error was reduced up to 8.41% in the case of the first experiment. Given these results, it is possible to assert that this kind of sensor can be used as a measurement tool. However, the average error observed suggests that this kind of device can be used only as an orientative tool because you need a luxmeter for calibrating every mobile phone model.  
Concerning the second hypothesis (H2), which stated that the smartphones' digital camera can be used as a lighting measuring tool, an extra functionality to the previous mobile application, in order to capture the required data from the digital camera, was developed. As in the previous hypothesis, the precision of the measurements when they are compared with a reference luxmeter was at a medium level, with an absolute error of 12.63%. For this reason, a calibration process was necessary in order to improve the accuracy of the data, having the possiblity to reduce this error up to 6.35%. These results highlight that a smartphone's digital camera can be used as a light measurement tool, asserting the proposed hypothesis.  
Furthermore, according to the third hypothesis (H3), the use of external sensors connected to the mobile device through Wi-Fi or Bluetooth provides measurements with a similar quality as  
Figure 12: External sensor device (Alcalux) vs. luxmeter accuracy.  
that obtained by the internal mobile sensors (ambient light sensor and digital cameras). To check the validation of this hypothesis, other measurements were performed with an external sensor that transferred all of the information directly to the mobile device through a Bluetooth connection. After studying all of the measurements, an average error of 2.70% was noted, meaning this hypothesis cannot be accepted due to the accuracy of the external device being higher than the others.  
In relation to the last hypothesis (H4), which stated that mobile devices can be used by any smartphone user as a fairly accurate light meter tool, we can assert that it is always possible that a pre-calibration process was performed for each device. However, the process of calibration may result in being difficult to be performed by users due to the fact that it requires the use of a calibrated luxmeter, which is not a common device for users. Furthermore, despite a complete process of calibration requiring an analysis performed by measuring sections, the accuracy obtained with just one calibration factor is enough to be used for a general purpose.