Cold-light cables for medical and technical use
Facts to know about cold-light cables
A constant ‘evolution’ of enhanced types of endoscopes and light-sources has shown the need for a standard-type of light cable to ensure a technically sound connection of light systems and instruments of different origin.
A wide range of system adapters is being offered to do so.
Generally, an endoscopic light cable is a flexible endoscopic accessory to combine a ‘light-giving’ system with a ’light-using’ instrument. Different cable diameters and lengths and a wide range of adapters ensure a handy connection of most brands available in the endoscopic market. Cold-light cables are in the product portfolio of most endoscopy manufacturers but being likewise offered by exclusive cable supplier. Each cable has a different focus on performance and its light-conducting fibers are either being coalesced or glued.
Based on a minor background on the ‘operating principle’ of light-cables medical users tend to decide for a non-optimal cable solution of their endoscopic system in use.
Some more details on light cables worthwhile to know…
Basic element of all fiber-optic units is the light-conducting ‘string’ which is consisting of a highly -refractive ‘glass core’ and a ‘glas jacket’ of much lesser refractivity. Light rays entering the fiber
at its front side are being transferred in the core part by total reflection at the interface core/jacket thus, following all deflections of the fiber to the exit point of the basic light guide unit.
A ‘glued’ light-cable with a diameter of 4,9 mm cross-section bundles about 4.000 single light-conducting fibers. The glass-jacket compared to the glass-core is made of a material with a much stronger refractivity in this way promoting a light transmission by means of total reflection. The angle for the transmission (opening angle) is about 60°, the light transmission by means of total reflection is performed without any quantifiable loss of light. Therefore, the light source is decisive for the most part of the ‘output’ of the light cable. Since the light transmission in cold-light cables generates a considerable heating-up any cable which are bundling fibers by gluing are inapplicable since the employed glue is not sufficiently heat-proof.
Cold-light cables with glued fibers are only finitely high-temperature proof !
Ultra-high-energy XENON light sources as well as state-of-the-art LED light sources can ruin in the shortest of time light cables with light-conducting fibers glued as a bundle.
Melted light cables are being specially worked up and compressed at the site of light entrance.
Their cross-section profile is hexagonal. At light entrance the material used is exclusively glass which cannot burn. By expertly compressing the single fibers into a bundle up to 20% more fibers can be installed which leads to a significant gain of light yield.
However, the user has to be aware that the heat transport through light source and light cable put the patient at risk for severe burn.
The medical user must exercise the utmost care when bringing high-energy light sources into use.
Light cable and the respective endoscope have to make a match. The cross-section of a light cable is depending on the amount of light entering at the endoscope.
Accordingly, a 4,9mm light cable combined with a urology endoscope is a clear mismatch because heat reflection can damage the telescope at the site of light exit. A basic 100 W light source would not harm a glued light cable where as a XENON light source definitely requires a melted light cable.
An appropriate ‚protection‘ of the light-conducting fibers will result in a clearly extended ‘lifetime’ of a cable in use.
In everyday life of a cable in use dragging it, falling on the ground and stepping on it can easily happen. Light cables which are merely coated with a single-layer silicone sheathing offer the advantage of being light-weighted and very flexible, still can be damaged quite easily.
A solid light cable the bundle of transmitting fibers offers a stable protection by use of a special glassware sheath especially against longitudinal loading whereas the maximum tensile loading is expected to be at 50kp. Bending and folding of the cable is prevented by use of an integrated stainless steel coil.
The outer sheath is a silicone tubing which is double-folded at the ends and serves as an additional kink protection. For hygiene reasons, it is placed in the inside of the sheath so that the outside provides a smooth surface. The metallic ends on which the adapters are being unscrewed need to insulated against each other. The high-voltage dielectric strength is defined at 6 kV.
Color-coding increases security!
From today’s point of view, it is advisable to exclusively employ welded cold-light cables. Only thus accidental burns at both sides of light entry and light outlet can be prevented.
Color-coded tubings have proven suitable distinguishing the respective diameter of cold-light cable.