The Spectroscopy Net
Gateway to Spectroscopy > Data Acquisition > Intensity measurement > repetitions


Number of independent intensity measurements

In Intensity I, the conclusion appears to be that the best results are achieved with a small number of measurements (3 or 4) with a long integration time. But perhaps there is a better way. To illustrate, let's choose a particular total measurement time, say 5 s. We collect a measurement every 0.1 s. We now have 50 individual measurements.

To estimate the mean we add the 50 values together and then divide by 50. Or we could put them into 5 groups of 10, take the mean of each group and then average the 5 groups. This is equivalent to changing the integration time from 0.1 s to 1 s. But we find that the two means are the same, even though the standard deviations are different. So perhaps the standard deviation is telling us something about how the intensity is varying rather than telling us how good the mean is. We can determine the confidence in the real mean m from

We can determine the confidence in the real mean m from where t[1-a/2;n-1] are the percentage points of Studentís t distribution.