a device for monitoring low levels of light emission in a selected underwr environment is provided with a photodetector having a light sensitive surface oriented into the environment , the photodetector generating electrical signals which are representative of light impinging upon the light sensitive surface . a window is positioned between the light sensitive surface and the underwater environment to protect the photodetector from the underwater environment , and a first material is positioned between the window and the underwater environment to prevent biological growth upon the window . a second material is placed in cooperative relationship with the first material to shift the wavelengths of certain light photons occurring in the underwater environment from a first wavelength range to a second wavelength range , in order to increase the attenuation lengths of the photons before they pass through the window .