# Biophotons: A Hard Problem
## 2 Methods and Experimental Data  
Our experimental setup was formed by a germination chamber, a photon counting system, and a turning filter wheel [17]. A drawing of the experimental setup we used to measure the spontaneous emission of germinating seeds is shown in Figure 1.  
The photon counting device a H12386-210 high-speed counting head (Hamamatsu Photonic Italia S.r.l, Arese (MI), Italy) powered at +5 Vcc. The phototube is sensitive in the wavelength range between 230 and 700 nm, with a peak sensitivity at 400 nm [24]. The data acquisition and control of the experiment were achieved via an ARDUINO board and a computer equipped with a LAB-VIEW system (National Instrument, Austin, TX, USA). The whole experimental setup work as a single-photon counting system and the detector can see a single photon with just the quantum efficiency of the photomultiplier. The acquisition time window was fixed at 1 s, and within this window, the entire system had a dark count of approximately 2 counts/sec, perfectly in line with the datasheet of this specific photomultiplier, which indicates 1.7 counts/sec [25]. A turning wheel holding a few long-pass glass color filters placed between the germinating seeds and the detector. The wheel had eight positions. Six were used for the color filters, one was empty, and the last one was closed with a black cap; see [17] for details. Seeds were kept in a humid cotton bed and placed in a Petri dish; they were normal seeds bought from a supermarket. Without any seed, the emission consists of a monotonic decreasing tail due to the residual luminescence of the material, a consequence of the light exposure of the experimental chamber. The emission tail arrives in a few hours at the dark count value. A typical measured signal with seeds and the wheel in the empty position is displayed in Figure 2. This signal (red points) refers to the emission of 76 lentil seeds for a total duration of 72 h from the moment of closure of the experimental apparatus after insertion of the Petri dish with the seeds into the measurement chamber. Figure 1: Schematic view of the experimental setup used in our experiment. The germination chamber is built with black PVC to avoid any contamination of light from outside. This figure is a part of Figure 1 in [17]. Figure 2: Biophoton emission of germinating lentil seeds. In the insert, a comparison between the emission of a single bean (orange curve) with that of lentil seeds (black curve); the two curves are the raw data (count/sec) averaged over one minute. This figure is depicted using the time scale for lentils. The capital letters in the figure indicate the main emission peaks observed in the experimental data. The initial behavior (a few hours) is dominated by residual luminescence. The germination-triggered biophoton emission emerges about 5-7 h after closing the chamber (the change in the slope of the counting curve), and then it became dominant for the entire duration of the experiment, with a signal well above the detector's dark counts. The temporal evolution of biophoton emission (see Figure 2) have a shape that appears to be a universal characteristic in the germination phase of seeds. For example, emissions from common wheat (_Triticum aestivum_) [14] and _Arabidopsis thaliana_ seeds [26] are very similar to those presented here. All this seems to indicate that the emission is substantially controlled by a completely general process, characteristic of the germination phase and substantially independent of the type of seed. This is quite interesting and needs a deeper discussion. The comparison [27] between the emission of the 76 lentil seeds and that of a single bean is reported in the inset in Figure 2. The emissions were analyzed for a fairly long time, from the end of the residual luminescence until the moment of the generation of leaves and roots.