What is linearity vs accuracy?

Linearity vs Accuracy in Optical Engineering

Linearity

Linearity refers to how well the output of an optical system or instrument maintains a straight line relationship with the input across its range. It is a measure of the consistency of an instrument's response to different levels of input. In mathematical terms, if the output directly scales with the input without deviating from a straight line, the system is considered perfectly linear. Linearity is crucial in ensuring that the performance of optical systems remains predictable and consistent across various operating conditions. It is often expressed as a percentage of full scale or in terms of linearity error.

Accuracy

Accuracy, on the other hand, denotes the closeness of an instrument’s measurement to the true value. It encompasses all types of errors, including linearity, but also takes into account systematic errors, random errors, and more. Accuracy is a wider concept that indicates the overall ability of the system to produce results that are close to the standard or true values. It is typically reported as a plus or minus value, representing the maximum deviation from the true value that can be expected under normal operating conditions.

While linearity focuses on the relationship between input and output values, accuracy evaluates the measurement's total deviation from the true value, considering all possible sources of error. An optical device can be linear but not accurate if, for example, it consistently measures a value higher or lower than the true value due to a calibration error. Conversely, a non-linear device could still be accurate at specific points if those points are individually calibrated.

In summary, linearity and accuracy are both critical parameters in optical engineering that evaluate different aspects of an instrument's performance. Linearity assesses the proportionality of input to output across the range of the instrument, while accuracy measures how close the instrument's readings are to the true values. Ensuring high linearity and accuracy is essential for the reliable and precise operation of optical instruments and systems.