Is low attenuation is a sign of good quality fibers?
Usually yes low attenuation is a sign of good quality fibers, but within lighting fiber optics the manufacturer's attenuation figures are often meaningless. To reasonable it is the only figure they can quote. Attenuation is measured by using a laser, a light emitting diode or a collimated light source. Within all three cases the light used is monochromatic, that means only one wavelength or a very narrow set of wavelengths is utilized.
The figures issued through manufacturers, per illustration: 150dB/Km refer to this single wavelength and consequent color that could be yellow or yellow/green. Similar fiber may have an attenuation of 750dB/Km upon the blue end of the spectrum and 400dB/Km upon the red side.
To compute the average attenuation for white light would include firstly analyzing the light of the lamp in the illuminator to find out its composition which could vary enormously, even for two identical lamps. After that one would have to measure attenuation in all individual wavelengths taking in account the amount of each current on the lamp's emission. At last, we would have to calculate to obtain a result that would only hold true for that lamp/fiber combination.
In order to be honest a close average can be worked out along with a few instruments but lamp deterioration because of aging, dust within the system and coloring of the common end because of solvent migration from the potting compounds, when used, soon make nonsense of averaged figures.