The natural law of open circuit voltage response of a silicon junction photovoltaic cell has been combined here with that obtained across the junction of a similar but nonilluminated cell due to an injected current, based on which a temperature independent, precision logarithmic light meter is developed. The range of the meter corresponds almost to the photosensitive range of the cell which in the present case is 10(-1)-10(+4) ix. The over-all theoretical response law obtained here has been checked experimentally at several points, and the accuracy has been found to be well within 1% over an ambient temperature change of about +/-3 degrees C. The logarithmic response obtained here is potentially very useful in instrumentation requiring analog computation with optical signals.