Anti-collision warning lights and method of use

Details Anti-collision warning lights and method of use Anti-collision warning lights and method of use

2000-11-20

2002-09-24

Mullen, Thomas (Department: 2632)

Communications: electrical

Visual indication

Using light emitting diodes

C315S18500S, C340S331000, C340S981000, C362S800000

Reexamination Certificate

active

06456205

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention concerns improvements relating to anti-collision warning lights and more specifically to a high-intensity anti-collision warning light and a method of driving the same for external use on aircraft.
In the field of anti-collision lights, there is a safety requirement to provide high-intensity regularly pulsed light on the exterior of an aircraft to enable the aircraft to be visible in all weather conditions. The intensity of the light is therefore quite high, typically being far greater than 100 Candela. Also, the flashing of the anti-collision light means that it is far more readily detectable than a light having a constant illumination. It should be noted that the flashing rate cannot be too high, namely above 25 Hz, because the light will be perceived by the human eye as being continuous. Furthermore, the intensity or intensity distribution has to be constant for each light flash.
Existing anti-collision lights, such as those described in U.S. Pat. Nos. 3,903,501 and 5,293,304, for example, use xenon flash tubes to generate the required intensity of light. The xenon flash tubes are driven by a discharge of an electrical capacitance into the flash tube, and so driving circuits include large banks of discharge capacitors. In addition, xenon flash tubes have high operating voltages that are generated in their driving circuits by transformers stepping up voltages to the required levels.
These requirements of often large, electrolytic capacitor banks and bulky transformers mean that the driving circuits tend to be large, heavy and expensive. This is particularly disadvantageous when several lights and their respective driving circuits are provided in an aircraft, where size and weight are very important issues. In addition, power consumption for these circuits can be undesirably high.
Conventional incandescent lamps that are used for aircraft navigation lights, for example, are far cheaper and require simpler, lighter driving circuits. However, incandescent lamps cannot generate the high intensity of light output required for warning lights.
It is desired to overcome at least some of the problems described above and to provide an alternative to existing high-intensity warning light technology.
BRIEF SUMMARY OF THE INVENTION
The present invention resides in the appreciation that light emitting diodes can be used to replace xenon flash tubes in anti-collision warning lights for aircraft, and can be appropriately controlled to generate the required high-intensity light output. Under normal operation, light emitting diodes cannot generate the required light intensity levels, and previously this has mitigated against the use of light emitting diodes in high-intensity light output applications. However, the inventors of the present invention have determined that by overdriving a plurality of light emitting diodes with a pulsed control signal, the light output can be dramatically increased without overheating or otherwise damaging the light emitting diodes.
According to one aspect of the present invention, there is provided an anti-collision warning light for external use on an aircraft, the anti-collision warning light comprising: a light source having a plurality of light emitting diodes which are arranged to be pulsed with an overdriving signal to produce a higher than normal intensity flashing light output; and means for generating the overdriving signal, the signal comprising a sequence of drive pulses, each driving pulse having a magnitude sufficient to cause said relatively high-intensity flashing light output, the light source and the generating means being arranged such that in use the intensity of the generated light flashes is constant and is at least 100 Candela per flash.
The use of light emitting diodes obviates the need for large banks of capacitors and bulky transformers that are required for driving the xenon flash tubes. The driving circuit of the present invention can be realized in a simple control circuit that generates the required series of drive pulses at a relatively low voltage. Accordingly, the control circuit can be significantly smaller, lighter and cheaper than that of the prior art anti-collision warning lights and also has far lower power consumption. This latter aspect is particularly advantageous as aircraft lights are mostly operated from a rechargeable battery power supply.
Another significant advantage of using light emitting diodes in place of xenon flash tubes is that the light emitting diodes need to be replaced far less frequently than flash tubes. For example, xenon flash tubes last a few hundred flying hours, whereas light emitting diodes can last tens of thousands of flying hours. The longer operational life and greater reliability of light emitting diodes (light emitting diodes are less likely to malfunction than xenon flash tubes) can also provide significant cost savings in the long term. This is not only because of reduced costs of replacement components but more significantly because of the reduced costs of maintenance and/or labor. Furthermore, light emitting diodes are far more robust than flash tubes with far greater resistance to shock and vibration. For example, the light emitting diodes of the presently preferred embodiment of the invention, can withstand 5000 G of force and also random vibrations without breaking down.
Flash tubes also require shielding to prevent the electromagnetic radiation generated by the high-voltage transformers from affecting other equipment in the proximity of the warning light. A further advantage of light emitting diodes over flash tubes is that there is no requirement for this electromagnetic shielding, because light emitting diodes do not require high-voltage transformers.
The generating means can be provided on the light housing to provide a self-contained compact lighting unit. Also, the generating means is preferably configured to be operable in response to a received timing signal. The timing signal can be provided by an appropriate flash pattern box which can be positioned, for example, remotely from the anti-collision warning light. The flash pattern box typically includes a microprocessor and associated memory, which produce timing control signals at an appropriate rate, which are used by the generating means to cause the light source to output light pulses, which are perceived as regular intermittent illumination or as a regular sequence of light flashes.
The light emitting diodes are preferably set out in an array. This advantageously allows the light emitting diodes to be provided in a compact unit with a high light output density. In addition, the array may comprise a plurality of groups of light emitting diodes, the groups being connected together in parallel and each group comprising a plurality of light emitting diodes connected in series. This arrangement incorporates built-in redundancy, which advantageously prevents catastrophic failure of the light emitting diode array, because if one diode fails, the whole unit will not also fail. Rather, the series or string of diodes, which contains the defective light emitting diode, will fail and the other strings of diodes will be unaffected.
Preferably, the light emitting diodes are arranged to output a selected color of light which is dependent on the selected mode of operation. This may be achieved by the light emitting diodes comprising selectable sets of light emitting diodes, each set being capable of emitting a particular color of light. In this way, a single array of light emitting diodes, for example, can generate different warning signals depending on the color of the light output.
A further advantage of using light emitting diodes in place of xenon flash tubes is that light emitting diodes generate specific narrow wavelength bands of light and for military aircraft applications the amount of infra-red light that is generated can be accurately controlled. Accordingly, the use of light emitting diodes is inherently night vision goggle (NVG) friendly because it does not blind pilots flyi

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