Luminance meter circuit

A luminance meter is an instrument that measures the brightness of luminous objects, such as TV screens, computer monitors, and oscilloscope screens. It uses silicon
photovoltaic cells as light-emitting devices and comes with filters, so that the spectral response of the calibrated silicon photovoltaic cells is close to that of normal human vision. The operation of the instrument
is simple, it is not interfered by surrounding stray light, and can directly read the brightness and illuminance values. It can also be used for low illumination measurements. The appearance and circuit of the luminance meter
are as shown in the figure.
    Figure b is the principle circuit. When the measured light is projected onto the silicon photocell , a photocurrent signal will be output. A current-to- voltage converter
composed of a pair of field effect transistors will convert it into a voltage signal, which will then be linearly amplified by 5G23. . In order to make the circuit have good linearity and high stability , a deep negative feedback network composed of R (or Rs) and Cz is used. Resistance wind, wind, R. . Adjust RP3~RP5 accordingly, and use a high-sensitivity ammeter to display the brightness value on a 100-2000d/m2 spherical surface.