## 3 Results and Discussions  
### Basic Benchmarking of the Imaging System  
The basic performance of the imaging system in terms of linearly responding to the level of luminescence of a sample at the same duration of acquisition was assessed using reflectance standards of various reflectivity that were exposed to the same level of illumination. The purpose was to examine whether the level of luminescence acquired was precisely proportional to the level of luminescence of the sample chamber since this was the basis for assessing subtle variations of the luminescence over time. An example of the linearity testing result is shown in Figure 5, where the inset at the lower-right corner of Figure 5B illustrates the spatial resolution of the imaging setup. As can be seen from the inset, the imaging plane was focused on the sample surface, which remained consistent with the use of different samples. Keeping the level of the sample surface ensured the consistency of comparing the luminescence from one or multiple configurations of the samples. The image of Figure 5A was taken from a reflectance standard of 99% reflectivity. The images taken from reflectance standards with the reflectivity ranging from 2% to 80% had a similar pattern of the vertical strip that appeared to be narrower in the shorter length and weaker in intensity than that of 99%. At the top of the vertical strip, there was a relatively faint zone, marked by a white circle in the figure, which corresponded to the projection of the tip of the light-delivery fiber. The vertical strip of which the top edge was tapered was caused by multiple reflections of the light between the flat, diffusively reflective surface of the reflectance standard and the surface of the imaging optics facing the sample. Thisset of acquisitions was made by tuning ON the irradiation while putting the acquisition time of the CCD imager at 1 \(\upmu\)s, the shortest exposure time possible. The light intensity was externally attenuated to ensure that at the 1 \(\upmu\)s exposure time, the CCD reading was not saturated by the diffusely reflected light from the reflectance standards of 99% reflectivity. We note that the geometric configuration of the light-delivery fiber with respect to the imaging optics dictated the appearance of the strip in this testing due to the reverberating diffuse reflections from the opposing planar surfaces. However, in the case of imaging, the delayed luminescence from a sample like yeast, no strip-like artifacts were observed. Replacing the reflectance standards differing in reflectivity in the sample holder was conducted according to the following sequences: (1) bottom-unloading the sample holder, (2) replacing the reflectance standard which would fit into a precise pocket, and (3) bottom-loading the sample holder to the light-tight chamber, then tightening the external harness of the light-tight chamber. The receding structures fabricated into the bottom-loading sample chamber made it possible to make the surface level/orientation of the sample and light-tight conditions consistent throughout the replacement of the eight reflectance standards. From the images taken with the reflectance standards, the intensity over the same fixed region (20 pixel-lengths along the line orthogonal to the strip, or that the pixels counted would be within the dashed circle at the lower aspect of the strip as shown in Figure 5A) were averaged. The averaged intensity is presented in Figure 5B as a function of the reflectivity of the reflectance standards. Excellent linearity was observed. This linearity indicates that the differentiation of any light intensity acquired by the imager over the same duration of acquisition shall reflect the difference in the luminescence of the sample falling within the collection aperture of the imaging device under otherwise identical conditions. This would ensure that the inter-sample differences in the luminescence are mapped correctly when associated with the same level of irradiation triggering the delayed luminescence.