What is the meaning of physical quantity $\nu$ in the expression of photon energy $h\nu$?

It is well known that, for an incident light of not so high intensity and in a certain range of frequency, the stopping voltage of photoelectric effect is independent of the intensity but dependent on the frequency of the light, which is described by the equation $V = h<br>u /e - {W_0}/e$, where $V$ is the stopping voltage, $h$ is the Planck constant, $<br>u$ is the frequency of incident light, $e$ is the electron charge, and $W_0$ is the work function. It means that the larger the frequency of incident light, the higher the stopping voltage is. However, the present experiment finds that for a non-monochromatic incident light, the stopping voltage is not determined by the maximum frequency component of the incident light, but by the maximum center frequency of all the wave train components (with different center frequencies) involved in the incident light, that is to say, in the photon energy expression $h<br>u$, physical quantity $<br>u$ does not refer to the frequency of a monochromatic light, but represents the center frequency of a wave train spectrum. The spectral bandwidth of a wave train component can be as large as 122 nm in visible and near-infrared region. This should arouse more attention in the study of energy exchange between light and matter.