Table 6. The experimental measured rates of retinal discrete dark noise in Luo et al’s paper [2] are converted to the unit of (cm⁻² s⁻¹) to be compared with the rates of UPE.

The rates are calculated as R_cm = 10⁸ R_μm in which $R_{\mu m}=\frac{N{R}_p}{S_{\mu m}}$ where S_μm is the area of the measured segment (in terms of μm²), S_cm is the area of the measured segment (in terms of cm²), N is the number of pigments in the measured segment, R_p is the rate constant per pigment (in terms of s⁻¹), R_μm is the rate constant in segment (in terms of μm⁻² s⁻¹), and R_cm is the rate constant in segment (in terms of cm⁻² s⁻¹). The results indicate that the obtained rates for dark noise are of the order of UPE rate (i.e. a few, up to 10⁴ photons/(cm²s)). [18–24, 27, 31–37, 41, 42] This results indicate that the retinal discrete dark noise can be potentially due to spontaneous cellular UPE (or biophotons) in photoreceptor cells.

Pigment	N	Sμm(μm2)	Rp(s−1)	Rμm(μm−2 s−1)	Rcm(cm−2 s−1)(UPE rate?)
A1 Bufo rhodopsin	6.0 × 109	7.5 × 65	4.18 × 10−12	5 × 10−5	5 × 103
A2 Xenopus rhodopsin	2.7 × 109	6.4 × 40	3.70 × 10−11	3 × 10−4	30 × 103
A1 Human red cone	6.5 × 105	Not specified [2, 43]	4.14 × 10−8	—	—
A2 Human red cone	8.1 × 105	Not Specified [2, 44]	6.70 × 10−7	—	—
A1 Mouse rhodopsin	6.5 × 107	1.4 × 20	6.64 × 10−11	1.5 × 10−4	15 × 103
A1 Bufo blue cone	3.3 × 109	7.3 × 37	9.39 × 10−14	14 × 10−7	140