It is known to use low power metal halide arc lamps in portable lighting systems. These low powered arc light systems are popular in bicycling and other outdoor pursuits where it is necessary to have a portable, high-powered light source. It is also often required to have the light source head or helmet mounted, or for it to be conveniently hand carried or worn on the body of a user. These requirements pose some problems with respect to the positioning of key components in the arc lighting apparatus.
Arc lamp technology cannot be simply powered from a low voltage battery. Arc lamps typically require a voltage pulse of around 6 kV to strike the arc and then typically 50-100V to continue running. An electronic ballast is required to generate the starting voltage and deliver the running voltage. Because of the high voltages involved, protection circuitry is also required to minimize the risk of arcing into the ambient environment in times when system integrity is compromised.
The control and ignition circuitry for low power arc lighting ballasts has always been physically combined on the same printed circuit board. In outdoor pursuit lighting applications, including bicycle lighting applications, this limits the number of ways that arc lighting systems can be positioned.
It is known to use a simple ballast that sits in a carry bag attached to the frame of a bicycle. Battery power is delivered into the ballast on one side via a cable. The output of the ballast unit is delivered to the lamp via high-tension cable.
This has the disadvantage that a double insulated cable able to withstand a 6 kV ignition spike without breakdown must be provided. Cable capable of withstanding such voltage stress is normally thick and bulky, which is not ideal for helmet-mounted systems, or systems where the light unit is hand-carried, where flexibility and ease of movement are desirable. Further, many users would be uncomfortable with the thought of such a high voltage pulsing around their body, in particular the head and neck region. There is a further disadvantage that in the event of cable damage (off road cycling is a sport that is particularly rough on equipment), arcing during the ignition phase of the lamp running cycle may prove hazardous. In diving applications, such a possibility is clearly even less desirable.
A further disadvantage is that the properties of the cable and the ambient environment may interfere with the ignition pulse and may affect starting reliability for the lamp. There is a modest upper limit to how long the cord can be else the lamp may fail to ignite.
An alternative known arrangement involves the entire ballast electronics being attached directly to the lamp with only low voltage cable running to the battery.
This addresses the issue of bulky and unsafe cables. However this arrangement does mean that the ballast electronics add significant size and weight to any helmet mounted system. This extra bulk can cause problems with helmet positioning and can put unwanted stress on neck muscles and joints. This issue is especially significant for riders who wish to use the equipment for extended periods such as 24 hour or ultra-endurance events.
In underwater applications, large lamp enclosures make for poor hydrodynamics, with bulky hand-held enclosures being difficult to manage especially in currents.
Also, the low voltage DC cable running to the ballast can be of sufficient length to introduce significant losses.
A further problem is that the componentry in ballast circuits is usually temperature sensitive. The presence of a lamp running nearby, generating significant amounts of heat, can make thermal management difficult.