Source: {"pile_set_name": "USPTO Backgrounds"}

The present invention is related in general to flashing warning lights, and, more particularly, to the provision of a high luminous intensity flashing warning light using superluminescent light emitting diodes for improved visibility and lower power consumption than conventional devices.
Flashing (i. e. intermittently or periodically illuminated) lights have long been used to provide visual warnings, and a considerable body of research has been compiled in the fields of physiology, psychology and engineering (and more recently in that hybrid field known as "human factors engineering") concerning human perception of flashing light (i. e. the ability of people to perceive and respond to flashing light). This field of study, which is inter-disciplinary, involves both the illumination art and the study of so-called psycho-visual or psycho-optical sensory phenomena.
From research and study in this field, a large number of factors have been identified and suggested as involved in the human perception of and reaction to flashing light, and although much knowledge on the subject is theoretically based and remains to be confirmed, there have been suggested certain factors which may be applied to the provision of a flashing warning light for improving the visibility of a flashing light, that is, for making a flashing light visible at a greater distance (i. e. "visibility"), and for enhancing the probability that people will not only perceive (i. e. see) the flashing light but will also react consciously thereto (i. e. "attention-getting").
It is suggested for example from the study of human factors that human visual perception of flashing light appears greatest when the light is flashed at a flash rate or frequency in the range of 3 to 10 flashes per second, with a flash duration of at least 0.05 seconds being recommended. Further, for the flashing of a light to be perceived as discrete flashes, the flash rate or frequency must be below the so-called "flicker-fusion" frequency, that is the frequency above which a flashing light appears as a steady light (i. e. due to the phenomenon of "persistence of vision"), this critical frequency being considered to be approximately 24-30 flashes per second.
For simplicity, hereinafter flash rate or frequency will be described in terms of "flashes-per-second" (fps).
Research has revealed other factors to be pertinent concerning perception of light in general, and flashing light in particular. For example, according to Fechner's Law the sensation of light as produced by the eye varies logarithmically with the intensity of the stimulus.
Luminance discrimination has also been experimentally studied, with regard to what psychosensory mechanisms are involved in discerning or seeing light flashes and in discriminating luminance differences between light flashes, in an attempt to establish psychometric curves for these functions. For example, it has been attempted to demonstrate that there are two discrete detection channels, one for long flashes and one for short flashes. Experiments have shown that different slopes are obtained for psychometric curves measured with short and long flashes. The explanation favored is that the visual system is not homogenous; there are at least two detection channels with inherently different slopes, and it is believed that these can be differentially tapped by varying test flash parameters. Results of some experiments tend to confirm this, and suggest that whereas the long flash detection channel is photometrically subtractive or subadditive, the short flash detection channel is photometrically additive and has a much steeper psychometric function slope than the long flash detection channel. It is further suggested that the psychometric function slopes of the different visual sensory channels vary differently as a function of wavelength, and it has been adduced that all three channels of the visual system do not have the same gain but rather differ in spectral sensitivity.
An interesting question concerns the relationship between the light detection and the flicker threshold. When flashes are supplied within a certain interval, they are perceived as being fused and are indistinguishable from continuously supplied light. It has been almost 150 years since it was shown that, under fused circumstances, the mean intensity over time is independent of the actual light-dark ratio. A further question concerns how many extra quanta of light must be added to flashes perceived as fused at the absolute threshold of vision to perceive a flickering light again, or more precisely, in order to see a regular high-frequency flickering light again (since fused light at threshold level is perceived as irregular flickering light). It is has been previously shown that the visual perception system's processing of quantal effects at low luminance levels is essentially nonlinear. Flicker can be detected either by the "on response" or by the "off response" of the visual system to a flash of light. In the case of the on response, extra light quanta have to be supplied so that the threshold set by the adaptational state induced by the previous stimuli is exceeded. A larger interval between flashes leads to a lowering of the adaptational state (because of a decrease of the flux) and thus to lower thresholds. In the case of the off response, the excitation state has to decrease by a certain amount in order to exceed the decrement threshold. If flashes last long enough for a stable adaptation level to be reached, then the threshold no longer depends on the actual flash duration. Experimental results have shown that after 100 msec this stable level can be reached and maintained by a constant intensity in the flashes.
With regard to critical fusion frequency as a function of mean intensity at low luminance levels, it is has been suggested that the critical fusion frequency increases from 6 to 25 Hz with increasing stimulus size. It has also been found that, at higher luminance levels, brief flashes need a longer interval to elicit flicker perception than do long-lasting flashes.
In summary, it may be concluded that simple flashes of light elicit a whole range of complex responses from the visual system relating to retinal potentials, subcortical potentials, primary-visual-cortex and associated area potentials, and generalized non-specific responses of the cortex.
Various different types of flashing lights have been known to be used for providing visual alert or warning lights, and have employed incandescent lamps, rare gas discharge lamps and, more recently, light emitting diodes as an illumination means, with some associated control circuitry. However, each of these previous types of illumination means has its disadvantages. Further, the design and operation of such previous types of flashing lights did not take into account the various factors such as flash rates and durations for optimizing the psychosensory perception of flashing light. Still further, the previous flashing light devices could not provide effective light output with low power consumption (i. e. efficiency) at desirable high flash rates, or could not do so without severely sacrificing device power consumption and reliability of the light source, and thus could not provide reliable low power operation and were thus not suitable for use in portable lightweight battery powered equipment.
For example, while incandescent light sources have commonly been used in flashing warning lights, there is the problem that, typically, incandescent light sources are not able to come to full brightness and to then cool off to extinction (i. e. turn on and off) within the higher optimum flash rate frequencies for attracting attention; the flashing character of tungsten-filament lamps is typically degraded significantly above flash rates of 9 fps. Furthermore, because of the inherent thermal inertia of incandescent light sources (once turned sufficiently on to emit light, there is a significant delay in extinction to the off state), such light sources cannot provide flashes of relatively short duration, nor can such light sources provide adequate on-off contrast when operated at higher flash rates. As a consequence, incandescent light sources are not suitable for use as warning lights at those flash rates and flash duration periods to which human visual perception is most sensitive but are constrained to use at lower frequencies and longer flash periods.
Still further, incandescent lamps are inefficient due to their emission of considerable energy at wavelengths outside the visual spectrum, and suffer inherent increased power loss, thermal inertia and filament degradation when operated at higher intensity and/or flash rates. An incandescent flashing light with adequate intensity for outdoor use usually requires larger size batteries to compensate for the excessive power loss in the form of heat, thus rendering it impractical for applications requiring reasonably small size and light weight necessary for portability. Durability of incandescent flashing lights is also degraded due to the thermal stress on the filament and mechanical shocks received by the filament.
Rare gas discharge lamps (e. g. Xenon, Argon flash tube lamps and strobes), while capable of operation at higher flash rates are, however, limited to extremely short flash durations which cannot be lengthened. Thus, such light sources are incapable of longer flash duty cycle operation. Furthermore, rare gas discharge lamps are relatively expensive and must necessarily be energized with high voltages and currents, and thus flashing warning lights of this type require complex charging and discharging circuits and consume considerable power. Furthermore, a large amount of energy is required to produce the flashing action of a rare-gas lamp; it tends to deplete ordinary batteries quickly if flashed at an optimal frequency of 3 to 12 Hz continuously such as that required by a warning light. Therefore, rare-gas discharge lights for extended flashing time are only feasible where a large power source is available, such as the utility power, or a power generator, but not in a portable application. Furthermore, being glass-encased, gas discharge flash tubes are susceptible to mechanical shock damage and to gas leakage rendering them inoperative.
Ordinary light emitting diodes (LEDS) are relatively durable mechanically and electrically (as long as their current supply is properly limited) and most readily lend themselves to low voltage-low current operation and electronic control for both flash rate frequency and duration. However such ordinary LEDs as have previously been used as light sources in flashing warning lights were of insufficiently low light intensity output. Hence the use of such low luminosity light emitting sources in visual warning devices has been of limited effectiveness, being restricted to subdued light environments such as for indoor activities, or where the ambient or background light level is quite low so that