Many lux measurement devices work according to this principle. They use one light sensitive cell. The sensitivity for visible light for this cell is for sure different than that of the human eye’s. The result is that the reading of the light cell is not giving a lux value. There are some ways to solve this issue:
(1) the cheapest kind of lux meters will have one correction factor applied, that corrects the measured value of the cell into the value that it should be when the sensitivity of a human eye would have been used. This works well, but as we will see later it requires a different correction factor for every light spectrum. However these lux meters work with one correction factor and of considerable errors are made when light is measured with a significant different spectrum (see further).
(2) the much more expensive lux meters with one cell are optimized and tuned with optical filters and lenses such that the sensitivity of this set of lenses and the cell itself directly matches the eye’s light sensitivity curve (so only one correction value needed for light of any spectral content). Very expensive lux meters come as close as 1.5 % uncertainty to the human eye’s sensitivity curve (class L which are the best), where this 1.5 % is true as an average value for the whole curve. Note that however a (much) larger error is to be expected when only a small spectral band is considered!
These type meters vary considerably in price, (1) differs from cheap (< 50 euro) to relatively expensive (> 250 euro), depending on the options like USB connectivity and sometimes pre-set values (read correction factors) for different type of light bulbs. And (2) are ranging from 800 euro to > 2000 euro, also depending on the options (temperature conditioned measurement head, computer connectivity etc).
These meters give the measurement result very quickly (< 1 second), as they have only one light sensitive cell that captures all visible light at once and converts that into a lux reading.