Color grading apparatus

A system for measuring the ratio of light reflectance of various products at two spaced areas of the light spectrum, comprising the combination of:

• means supporting the product to be measured;
• light source means for directing light including the two areas of the light spectrum onto the product;
• a pair of first and second light sensitive cells for generating light responsive signals in response to the light received;
• first means to direct light reflected from the product in a first area of the spectrum onto a first light sensitive cell;
• second means to direct light reflected from the product in a second area of the spectrum onto a second light sensitive cell;
• first and second amplifiers receiving the light responsive signals from the first and second light sensitive cells, respectively, and for generating output signals responsive thereto:
• means to receive and compare the output signals from the amplifiers and generate a signal in response to the ratio of the signals;
• readout means for indicating the ratio of the signals;
• a calibrating disc having a known ratio of light reflectance in the first and second areas of the spectrum positioned to receive light from said light source means and reflect light to the first and second means at preselected time periods onto the light sensitive cells;
• and
• means to adjust the level of amplification of one of the first and second amplifiers for adjusting the readout to said known ratio reading during said preselected time periods.