Before getting to know what resolution stands for, you need to know what “ lp / mm “ means. It means line pairs per millimeter (lp / mm). These units are used for measurement of image intensifier resolution. How close lines can be to each other and still be visibly resolved, this determines the quality of resolution. Line pairs are composed of a dark line and the nearest bright line. A line can be dark or bright. For example, a resolution of 20 lines per millimeter means that 10 dark lines and 10 bright lines are alternating or 10 line pairs per millimeter (10 lp / mm). The more line pairs the better the resolution the higher the price of the product. The best night vision optics on the market use a resolution with 64+ lp / mm.
Tube resolution is measured in line pairs per millimeter (lp / mm), system resolution is measured in cycles per milliradian (cy / mr). Tube resolution is important if you are comparing the quality of optics and filters. Mostly resolution is measured at low-light and high-light conditions. The optimal resolution should be at a point between very low-light and very high-light conditions. Image resolution (lp / mm) will remain always the same, while the system resolution (cy / mr) is affected by altering eyepiece or objective and with adding a relay or magnification lenses.
Maximal resolution is a parameter measured at the highest light conditions.
If we put everything together, when comparing different night vision optics, the higher the price, the higher the quality, what determines the ability to present a sharp image. Notice also, night vision with lower resolution will maybe produce good results in higher night-light conditions with more ambient light, but performance in darker conditions will not be so good.