Nominal sizes serve as "general descriptions" for lighting manufacturers when identifying a range or category of products. The nominal size of a unit is typically not the same as the exact measurement of the product. Instead, the nominal size can be referred to as a standardized dimension for a set of or several units in the same series.
What is Nominal Length of LED Tubes?
For example, a standard 3.54-inch floppy disk that holds 1.44 megabytes as the nominal capacity may have an exact capacity of 1,474,560 bytes. Furthermore, in the lumber sector, boards with a nominal measurement of 2 x 4 may have exact measurements that are closer to 1.5 x 3.5 inches. When one goes into a store and asks for a 2 x 4 board, he or she will likely end up with a piece that does not have an exact 2 x 4 measurement.
Nominal values are designed to streamline descriptions or conditions that are applicable to a range of very similar products. Out of convenience, individuals could refer to the nominal value of the product when talking about specific units in the same series or group. The generalized figure or accepted condition does not override the real value of the measurement. It is merely an official representation, but not the reality of the actual figure. One should consider that a nominal value is not the average measurement or condition of a group of similar products in a series. Nominal standards are set by the relevant industry it applies to.
The need to refer to nominal sizes is steadily increasing, as techniques for measurements and determining conditions are getting more accurate. For example, a 10-inch pencil measures 10 inches using a traditional ruler. As a result, the manufacturer then released the product as a 10-inch pencil. But later on, with a laser-accurate measuring device, that same pencil was measured again and was discovered to be exactly 10.0038 inches. A few more years after, an atomically-accurate measuring tool was used to measure the pencil and it turned out to be 10.000000005 inches. The manufacturer will likely continue to sell the product nominally, as a "10-inch" pencil (despite it not being exactly 10 inches), and possibly mention the exact measurement on the label.
Nominal figures are also used to gauge a range of tolerance levels. For example, when talking about nominal voltage standards in North America, the general accepted value is 120 V. Voltages that are +/- five percent of 120 V, i.e., between 114 V to 126 V, are still tolerated under the nominal voltage standard.
In the industrial lighting sector, to determine the nominal length of an LED tube, one could take an end-to-end measurement from the back of the socket on the fixture (do not simply measure the bulb). Alternatively, because these figures are already well-established in the lighting industry, one could simply refer to a universal nominal length chart for the specific unit.