A uni-directional test will be conducted on all pigtail splices with no greater than a. 8 dB after 5 repeated attempts results in the replacement and re-splicing of that pigtail. To be able to judge whether a fiber optic cable plant is good, one does a insertion loss test with a light source and power meter and compares that to an estimate of what is a reasonable loss for that cable plant. Testing with. Optical fibers can be joined together, such that light is efficiently transferred from one fiber to another. The transmission principle is 'total reflection of light'. Generally, a light-emitting diode. At TREND Networks, we are frequently asked how much loss is allowed when conducting testing on fiber optic cabling. So how do you determine acceptable loss? When testing fiber optic cabling, determining acceptable loss is. However, the effect of Fresnel reflection at a fiber–fiber connection can be reduced to a very low level through the use of an index-matching fluid in the gap between the jointed fibers.