One stop is a factor-of-two increase or decrease. In optical systems, dynamic range is often expressed in stops. If a voltage-monitoring system, for example, has a dynamic range of 80 dB, the maximum detectable input level is greater than the minimum detectable input level by a factor of 10,000. If we apply a stricter interpretation of dynamic range, we would not allow changes in pupil size, since this is analogous to moving the upper or lower limit by increasing or decreasing gain.Ī dynamic range is really just a ratio: you take the maximum signal level and divide it by the minimum signal level.Įlectrical engineers tend to use decibels to express large ratios (such as the gain of an op-amp), and dynamic range is no exception. To determine the dynamic range of human light detection, we need to evaluate our ability to perceive a range of luminance while looking steadily at one scene. Thus, the range doesn’t apply to input signals that are dynamically varying between upper limit and lower limit and thereby restricting the system to a certain set of operating conditions. The luminance range to which the human eye is sensitive spans fourteen orders of magnitude: the lower limit is about 10 –6 candelas per square meter (cd/m 2), and the upper limit is about 10 8 cd/m 2.ĭoes this mean that the human visual system has a dynamic range of 10 14? No, because the luminance range mentioned above includes the sensitivity of both cone and rod cells, and these two biological photoreceptors don’t provide simultaneous operation (the system actually needs a significant amount of time to transition from its high-luminance mode to its low-luminance mode). We can see ripples on a moonlit pond and a white sail gleaming under a blinding Mediterranean sun. ![]() The human visual system has a remarkable capacity for variations in input magnitude. With the foregoing information in mind, we can say that dynamic range, in the context of electrical engineering, specifies the range of possible or acceptable values that a dynamic signal can assume when delivered to or produced by a given system. With dynamic range, we still have upper and lower limits, but these limits apply to systems that are constrained by the continuous variation of input or output phenomena, and they capture the capabilities of the system with respect to operating conditions that reflect the dynamic nature of the relevant signals. ![]() “Dynamic”-essentially the opposite of “static”-describes that which is continuously moving and changing. Thus, static range suggests a region of possible variation in which the limits are not constrained by the need for input or output phenomena to actively and unpredictably move between the upper and lower limits. “Static,” from a Greek verb related to standing or motionlessness, denotes a lack of movement, action, or change. “Range” is defined as the region of variation between two limits. But let’s pretend that it does and use it to clarify the nature of dynamic range. ![]() In my opinion, it’s surprisingly difficult! In any case, I hope that by the end of this article we’ll all be ready with a solid explanation when someone stops us on the street and asks, “Hey, could you tell me what dynamic range is?”Īs far as I know, the term “static range” doesn’t exist. One term that electrical engineers confront regularly, and in a variety of contexts, is “dynamic range.” Before you continue reading, take a minute and try to formulate a precise, comprehensive definition. Discussing technical details, mathematical relationships, and performance specifications is not always easy, and we can make the task more manageable and productive by striving to carefully employ and thoroughly understand the relevant terminology. In the world of engineering, though, we place greater emphasis on precision and clarity. This is part of our natural linguistic faculty and usually doesn’t cause any problems, especially in ordinary conversation. An interesting phenomenon of language is that we often understand words that we cannot define.
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