FLASHLIGHT WITH ADJUSTABLE LIGHT OUTPUT

FIELD OF THE INVENTION

The current invention is related to a flashlight comprising a mercury vapour discharge lamp with an adjustable light output and method for operation such a flashlight.

BACKGROUND OF THE INVENTION

In US 2005/0128741 Al such a flashlight having a lamp, a power storage element, a switch, and an electronic controller is described. The controller has a switch input connected to the switch and operates in response to the input to deliver power from the power storage element to the lamp. The controller may be directly connected to each of the lamp, source, and switch. The switch may include several separate contact elements operating sequentially in response to movement of a switch actuator. The controller may provide different illumination levels and functions in response to different pressures and durations of actuation. The flashlight may include a dimmer level control to establish an intermediate "dimmed" output level, and operate to provide the selected dimmed output when the switch is depressed by an intermediate amount, and to provide a greater maximum output level in response to full actuation of the switch. It is stated in the patent application that arc lamps as e.g. vapour discharge lamps or more specifically "high pressure discharge lamps" or "HID lamps" (High Intensity Discharge Lamps) and "UHP-Lamps" (Ultra High Performance Lamps) can only be used in variable output light source in combination with a second lamp. The problem is solved by using a LED that operates efficiently over a wide range of input power to produce a wide range of possible light outputs. Further it's proposed to use an array of LEDs in order to generate sufficient light output. The proposed solution does have the disadvantage that a single

LED doesn't provide high light output favourable for high-end flashlight and distributed light sources as an array of LED do have relatively low peak intensity not favourable for signalling functionalities.

SUMMARY OF THE INVENTION

It is an objective of the current invention to provide an improved flashlight with adjustable intensity.

The objective is achieved by means of a flashlight comprising: - a mercury vapour discharge lamp; an electrical power supply; a system control unit being arranged in a way that the power supply of the mercury vapour discharge lamp can be regulated at least between two different power level; - a regulator, and the regulator is arranged in a way that the power supply of the mercury vapour discharge lamp can be regulated by means of the regulator via the system control unit.

In contrast to the cited prior art only one lamp, a mercury vapour discharge lamp, is needed in order to get an adjustable flashlight with high peak intensity. Mercury vapour discharge lamps comprise an envelope, which consists of material capable of withstanding high temperatures, for example, quartz glass. From opposite sides, electrodes made of tungsten protrude into this envelope. The envelope, also called "arc tube" in the following, contains a filling consisting mainly of mercury, and also one or more rare gases. By applying a high voltage across the electrodes, a light arc is generated between the tips of the electrodes, which can then be maintained at a lower voltage. Mercury vapour discharge lamps offer excellent optical properties as point- shaped light source, a luminous intensity-as high as possible- accompanied by a spectral composition of the light-as natural as possible-with respect to flashlight applications. These properties can be optimally achieved with so-called "high pressure gas discharge lamps" or "HID lamps" (High Intensity Discharge Lamps) and, in particular, "UHP- Lamps" (Ultra High Performance Lamps).

Usually, the arc tube of such a high-pressure discharge lamp is of very small dimension, e.g. having a volume of some 10 mm ³ . The high electrode load of such a lamp results in evaporation of tungsten from the electrodes. The tungsten is then deposited on the wall of the arc tube, leading to a very undesirable blackening of the arc tube. Such a blackening of the wall must be avoided, otherwise the wall temperature of the arc tube increases during the operational life time of the arc tube, due to increased absorption of thermal radiation, ultimately destroying the arc tube. In an attempt to avoid such wall blackening due to tungsten transport, precise amounts of oxygen and halogen, preferable bromine, have been added to the gas in the arc tube. Such additives to the lamp atmosphere prevent the tungsten, that evaporates from the electrodes, from the deposition on the bulb wall, since, in the cooler regions of the bulb close to the bulb wall, the tungsten atoms react chemically to form volatile oxyhalide molecules which are transported, e.g. through convection, to the hotter regions of the lamp near the electrodes, where the molecules dissociate. In this way, tungsten atoms are returned to the lamp electrodes in a regenerative manner. This transport cycle is usually called the "regenerative cycle".

A problem arises if the lamp is driven with an operational power much below the nominal power of the lamp. Below a certain power level, the mercury condenses, with the result that the halogen, e.g. bromine, is dissolved into the liquid mercury. The regenerative cycle is thus no longer effective.

However, for high power mercury vapour discharge lamps with a power input above IOOW it has been shown that alternating operation between extreme dimmed level and nominal power-i.e. with and without a regenerative cycle-results in a cleaning of the quartz wall. In other words, by constantly monitoring the periods in which the lamp is operated in the saturated and unsaturated operation regimes, and by judiciously switching between these states, it can be ensured that no significant blackening of the inner walls arises during the total operation time of the lamp. The term "saturated operation regime" describes the operating regime of the lamp in which so much mercury condenses in the arc tube to interrupt the regenerative cycle, normally resulting in a significant blackening of the walls of the arc tube. On the other hand, the term

"unsaturated operation regime" describes that operating regime in which the mercury has

evaporated to such an extent that the regenerative cycle remains essentially undisturbed. During signalling with a flashlight the periods of working in the saturated operation regime are rather short (some seconds). In general the time period working in the saturated operation regime can be directly regulated by means of the regulator via the system control unit. The system control unit regulating the power supply of the mercury vapour discharge lamp has only to monitor whether a defined time limit (in general several minutes) is reached in order to prevent irreversible wall blackening. In the case this time limit is reached the mercury vapour discharge lamp is switched back by means of the system control unit to the unsaturated operation regime by increasing the power level. The power supply of the flashlight can be one or more batteries respectively rechargeable batteries. The regulator can be a simple switch or a combination of two switches, a first one for switching on and off of the flashlight and a second one for regulating the light output of the flashlight. Whereby special embodiments of the switch are a button or a rotary switch. Further the regulator can be a more sophisticated device for controlling the functions of the system control unit as discussed below. In addition there can be at least two power levels those can be activated via the regulator where the mercury vapour discharge lamp works for an unlimited time period in the unsaturated operation region. This feature can be used to offer e.g. an energy saving operation mode to the user of the flashlight. In a further embodiment of a flashlight according the current invention the system control unit is arranged in a way that the power supply of the mercury vapour discharge lamp in at least one power level is timed by the system control unit. Using mercury vapour discharge lamps with an input power much lower than the nominal power a cleaning of the quartz wall of the mercury vapour discharge lamp doesn't happen. At a power level of around 40 W and less the halogen cycle does not function properly. Consequently a blackening of the walls has to be prevented at all. This problem is solved by a technical adjustment in the system control unit. The system control unit is arranged in such a way that by activating the regulator the driver dims the lamp but not longer than a maximum allowed time period determined by the thermal inertia of the lamp since the temperature of the lamps determines when the saturated operation region starts. If the maximum allowed time period is reached the system control unit

automatically increases the lamp power to its minimum value at which the unsaturated operation region is reached. In this way, the averaged power of the lamp is high enough to ensure that the halogen cycle functions. Hence, wall blackening will be prevented at all, and signalling will not have harmful consequences for the lifetime of the lamp. Frequently switching between the two power levels, even on very short time intervals, does not have any harmful consequences for the lamp, and does not lead to a premature lamp failure. The advantage of the low power mercury vapour discharge lamp is that less battery capacitance is needed or alternatively longer operation times are possible. Further the system control unit can be specified in a way that the power supply of the mercury vapour discharge lamp can be regulated between two power levels, a high power level and a low power level and the time period of the low power level is timed by the system control unit. In addition the system control unit can provide two timing periods those can be regulated by means of the regulator. That means the regulator e.g. a button can activate a short predetermined time period of low power level via the system control unit by shortly pressing the button and additionally a predetermined longer time period (being maximum as long as the maximum allowed time period) of low power level via the system control unit by holding the button. All these measures can also be used together with mercury vapour discharge lamps with an high nominal input power above IOOW less suitable for flashlights (depending on available battery capacity). A further embodiment of the flashlight according the current invention further comprises an adjustable filter being arranged in a way that the illumination of the flashlight can be controlled independently from the power supply of the mercury vapour discharge lamp by means of the regulator via the system control unit. The adjustable filter can be a mechanical device as an adjustable aperture or alternatively a transparent substrate placed at the aperture of the flashlight whereby the transparency of the transparent substrate can be adjusted. The transparent substrate can e.g. be a glass or polymer substrate with a thin layer whereby the transmission of the layer can be electrically regulated, a glass or polymer substrate with electrically adaptable absorption or an LCD device as used for LCD displays. Further polymer-dispersed liquid crystals (PDLC) offer the possibility to adjust the transparency. The adjustable filter can be used to provide an independent control of the light output of the flashlight by adding e.g. an

independent switch to the regulator or the adjustable filter is synchronized with the regulation of the power supply of the mercury vapour discharge lamp. In the latter case the transparency of the transparent substrate is reduced at the same time when the power supply of the mercury vapour discharge lamp is reduced. This measure can be used to increase the ratio between the maximum available light output and the minimum available light output in order to improve the signal quality. Further this measure can be used to increase the temperature of the mercury vapour discharge lamp in the low power level by reflecting and/or absorbing the light by means of the transparent substrate or the adjustable aperture. This reduces the condensation of the mercury and enables even lower minimum power level of the mercury vapour discharge lamp or longer time periods of the mercury vapour discharge lamp at the low power level without causing blackening of the Quartz wall.

In another embodiment of the flashlight according to the current invention the system control unit is arranged in a way that at least one defined sequence of signals implemented in the system control unit can be activated via the regulator. The regulator can e.g. comprise an additional switch in order to activate a predefined sequence of signals as e.g. SOS. Further the regulator comprises a more sophisticated interface offering several predefined sequences of signals those can be activated via the regulator. Additionally the possibility of defining a sequence of signals by the user can be implemented.

It is further an objective of the current invention to provide a method for operation of a flashlight with an adjustable light output comprising a mercury vapour discharge lamp.

The objective is achieved by means of a method for operation of a flashlight comprising a mercury vapour discharge lamp comprising the steps of: supplying the mercury vapour discharge lamp with electrical power at a high power level; reducing the electrical power supply of the mercury vapour discharge lamp for a predefined time period by means of a regulator to a lower power level and automatically switching back the electrical power supply of the

mercury vapour discharge to the high power level after the predefined time period. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be explained in greater detail with reference to the figures, in which the same reference signs indicate similar parts, and in which:

Fig. 1 shows a cross-sectional view of one embodiment of the current invention.

Fig. 2 shows an exploded view of the exterior components of one embo diment o f the invention.

Fig. 3 shows an exploded view of the internal components of one embodiment of the current invention.

Fig. 4 shows a principal sketch of a mercury discharge lamp.

Fig. 5 shows a principal sketch of a further embodiment of the current invention.

DETAILED DESCRIPTION OF EMBODIMENTS

In Fig. 1 a cross-sectional view of a first embodiment of the current invention is depicted. A mercury vapour discharge lamp 12 is connected to a system control unit 18. The system control unit 18 drives the mercury vapour discharge lamp 12 by means of an electrical power supply 26. The system control unit 18 is regulated via a regulator comprising a first button 7 and a second button 8. The first button 7 is used to switch the flashlight on and off. The second button 8 regulates the power supply of the mercury vapour discharge lamp 12 by means of e.g. decreasing or increasing the power applied to the mercury vapour discharge lamp 12 via the system control unit 18.

Fig. 2 shows an exploded view of the external components of a flashlight according to the current invention. Essentially a front cap 1 with the aperture of the flashlight, a front screen 4, a reflector 5, the reflector housing 6, the battery housing 9 the first switch 7 and the second switch 8, the end cap 10 and a protective cap 11 are shown. The focal point of the flashlight can be regulated by means of the reflector

housing 6 being in a fixed connection with the reflector 5.

Fig. 3 shows an exploded view of the internal components of a flashlight according to the current invention. It is depicted how the mercury vapour discharge lamp 12, the system control unit 18 and the power supply 26 can be fixed in the housing of the flashlight. Further a connector 30 is shown that can be used for recharging a rechargeable battery being part of the power supply 26 and optionally to provide a data connection to the system control unit 18 in order to reconfigure or add functions of the system control unit 18.

Fig. 4 shows a principal sketch of a mercury discharge lamp 12 that can be used in a flashlight according to the current invention.

Fig. 5 shows a principal sketch of a further embodiment of the current invention. The light output of the flashlight is additionally regulated by means of the front screen 4 being arranged as an adaptable filter. The adaptable filter comprises a layer of polymer dispersed liquid crystals (PDLC) sandwiched between two glass layers with transparent (ITO) electrodes. As long as a voltage is applied between the transparent electrodes the adaptable filter is transparent. If no voltage is supplied the PDLC layer scatters the light reducing the maximum light intensity per solid angle. The transparency of the adaptable filter is regulated by means of the regulator via the system control unit 18 synchronously to the power supplied to the mercury vapour discharge lamp 12. That means, if maximum power is supplied to the mercury vapour discharge lamp 12 the transparency is maximized and if minimum power is supplied to the mercury vapour discharge lamp 12 the transparency is minimized, maximizing the relation between maximum and minimum light output of the flashlight for improved signalling. The connector 30 is directly connected to the system control unit 18 in order to program or reprogram signalling sequences that can be activated by means of the regulator. The latter can be done by e.g. rotating switch 7 (without affecting the on state of the flashlight) from a first neutral position to second position corresponding to a first sequence of signals (e.g. SOS) and activating or deactivating the sequence of signals by means of pushing the second switch 8. In the neutral position of switch 7 the signalling can be done manually by means of the second switch 8.

The present invention will be described with respect to particular embodiments and with reference to certain drawings, but this is not to be construed in a limiting sense, as the invention is limited only by the appended claims. Any reference signs in the claims shall not be construed as limiting the scope thereof. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn to scale for illustrative purposes. Where the term "comprising" is used in the present description and claims, it does not exclude other elements or steps. Where an indefinite or definite article is used when referring to a singular noun, e.g. "a" or "an", "the", this includes a plural of that noun unless specifically stated otherwise.

Furthermore, the terms first, second, third and the like in the description and in the claims are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances, and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

Moreover, the terms top, bottom, first, second and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein.