In the past, it has been particularly difficult to provide a completely waterproof submersible lamp which is able to withstand knocks and vibrations in use while being able to maintain waterproof integrity. This problem is particularly manifest in the tail lights of boat trailers but can also be present in other motor vehicle situations, and in other locations such as in underwater lights in swimming pools or in areas which are often subjected to high pressure water treatment.
In a trailer-like situation, the problem is made worse by the necessity to provide different colored lenses within a single light. For example, the tail and brake lights of a motor vehicle must have a red lens, the turn indicator light must have an amber lens and there is also often the necessity to provide a clear lens section for illuminating the adjacent number plate of the trailer or other motor vehicle. It has proven extremely difficult to manufacture conventional combined tail/stop/indicator/number plate lights which will maintain waterproof integrity at the joints of the various different colored lamp segments. It is of course possible to provide individual lamps for each of the above functions but this significantly increases the cost and also the complexity and "untidiness" on the motor vehicle.
The legal requirements of many countries also make it necessary for the various lenses to have certain light focusing or diffracting characteristics and it has proven extremely difficult to provide these characteristics in a waterproof tail light or indicator light lens of the type described above.
There are also many situations where it is desirable to provide a waterproof entry for an electrical cable into an apparatus. In the past, in some instances, an elastomeric collar or O-ring is provided which forms an interference fit with the outer sheath of the cable to inhibit the influx of water. In other cases, the cable passes through a bush or collar and is "potted" in place using a setting chemical compound such as a silicon based compound or an epoxy resin. Such waterproof entries can work loose over time, particularly in situations subject to high vibration or stress loadings which will then allow the ingress of water into the apparatus. Furthermore, if the outer sheath of a multi-conductor electrical cable becomes ruptured or pierced, water can enter into the housing through the cable sheath, even if the entry point remains intact about the external perimeter of the sheath.