Extech sdl400 light meter and data logger extech sdl400 the extech sdl400 light meter with data logger records data on an sd card in microsoft excel reg format for easy transfer to a pc for analysis the user can manually store 99 readings or set the logger to automatically store up to 20m samples with date and time stamp at a user selected sample rate the meter uses a precision silicon photo diode and spectral response filter to give a wide range of cosine and colour corrected measurements