Light meter linearity is a crucial factor in using a light meter in varying levels of illumiunation or luminance and should be checked prior to purchasing a meter if at all possible.

I took one of those black card sheets for displaying a selection of 6x6 trannies and in each aperture I placed a different Wratten ND gel - all the way to an ND 3.0.

Over that 10 stop range both my Zone VI modified Pentax Digital Spotmeter and my Minolta V perfromed within 0.10 of a stop over the entire range. Concversely there are major brands that I have tested in shops which have not even been acceptably linear in their response even over the 4 or 5 stop range of most colour photography for reproduction.

It is a simple test to carry out once the sheet is made up and I regularly check to ensure that everything is happening just as anticipated. I work primarily for interior designers and architects and the values in an interior can be very critical in maintaining the design integrity of tonal differences.

Another worthwhile test to carry out is to direct the cell at an electric stove element in a darkened room. Take a reading and then turn on the element and read again BEFORE any visible redness shows in the hotplate. If the meter indicates a difference in exposure then the IR screening is not satisfactory.