Patent Publication Number: US-6992591-B2

Title: Marker lights for wireless doorbell transmitters and other devices

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to low intensity level luminairies, particularly for use marking the location of doorbell buttons, driveway edges and the like, and more particularly relating to a battery powered luminaire providing a useful battery life of one or more years. 
   2. Description of the Problem 
   Since the introduction of wireless doorbells, customers have requested a lighted button feature to assist in locating the doorbell button in the dark. Lacking connection to line electrical power, providing such a feature has proven impractical to achieve with even the smallest incandescent sources. The power demands of incandescent bulbs exhaust the capacity of typical battery sizes usable in these products within hours, or days, at best. Larger batteries could increase battery life, but these are costly and their bulk is not appropriate in the application of a doorbell button. Early, non-high intensity type, LED light sources, while operable for far longer periods than incandescent sources, still cannot operate at the very low current levels required to obtain desirable battery life objectives of one year or longer while emitting useful levels of light. 
   Other products could benefit from a battery powered, long life light source suitable for use in a wireless doorbell. Self-contained battery powered chimes hardwired to a door mounted push button are very common in Europe, although somewhat rare in North America. Lighted buttons are a desirable feature here as well, but cause the batteries in the chime to become quickly exhausted. Thus battery chime systems have not included a lighted button. Presently, incandescent bulbs and low efficiency LED light sources are used in lighted buttons, but they consume far too much current to provide acceptable battery life in battery powered chimes. 
   Battery life can be extended for an LED device by causing the LED to blink on and off. This can also serve to attract attention to the device. For a residential application however, most consumers do not want to have a blinking LED marking their doorbell, driveway, or sidewalk. Operating the LED on a continuous basis may be more attractive to consumers, but would require substantially more power. 
   Reflector based markers and some types of landscape lights could also benefit from a long life battery powered luminaire. Roadside, bicycle and driveway reflector products are very effective when a bright source of light shines directly on them. Otherwise, such reflectors are ineffective. A self-lighted marker has the advantage of being visible without an external source of light directed on it, so that it is visible to walkers, joggers and bicyclists at night. Such a marker would also be useful in driving situations where the marker is outside the normal field of the car&#39;s headlights. Roadside reflectors have been proposed that have made use of solar charging systems for batteries. Rechargeable batteries are bulky and the solar cells and recharging circuits can add substantially to the relative cost of the product. Solar cells must be placed in locations that receive direct sunlight during some part of the day, and, as a consequence, may not work in a shaded location. During winter at high latitudes very little sunlight is received, reducing the effectiveness of these products. 
   Under conditions of darkness, it does not require much light output to make an object visible. The human eye has great light intensity adaptability. The differences in eye sensitivity between conditions of bright sunlight (photopic vision) and fully night adapted vision (scotopic vision) can vary by a factor of 25,000 and instances of adaptation up to a factor of 1,000,000 times have been documented. Multiple mechanisms within the eye provide this adaptability, some responding quickly to changing light conditions, e.g. pupil dilation, and some slowly, e.g. maximum rod sensitivity, so that fully night adapted vision is not achieved for up to 30 minutes. The implication of this is that levels of light useless under normal indoor lighting conditions, can become useful under conditions where one can anticipate people will have adapted to darkened conditions. The spectrum of light generated makes a difference in the minimum radiant intensity required for human perception. Generally people can see broad spectrum or white light more readily than they can see narrow spectrum light of the same intensity. 
   Visible spectrum applications of light emitting diodes have long included simple status indicators and dynamic power level bar graphs. Display applications have grown in number and super bright LEDs are used in various automotive and traffic signal applications. Super bright LEDs are extremely efficient in terms of the percentage of input power converted to visible radiation compared with devices previously known. This is one reason they are favored for applications requiring the output of high intensity light. Super bright LED devices are available which emit any one of a variety of colors, or which emit broad spectrum radiation. Some super bright LEDs also work over broad ranges of drive currents and emit low intensity light at low drive currents and with low power consumption. These LEDs exhibit efficiencies at low power levels comparable to the high efficiencies achieved at the much higher power levels at which they are designed to operate. U.S. Pat. No. 6,140,776 to Rachwal teaches a flashlight that exploits low power operation of super bright LEDs in one application. 
   SUMMARY OF THE INVENTION 
   The invention provides a marker luminaire combining a super bright LED and a low energy drive circuit to promote long battery life. Such a luminaire comprises a housing and a lamp disposed in the housing capable of producing light visible to a partially darkness adapted human eye. A minimal current is selected to produce enough light to be seen at the desired distances. A light scattering element is optically associated with the lamp to make the marker light visible across a wide viewing angle and thereby indicate the location of the housing. The electrical drive circuit provides the minimal current to the lamp. The electrical drive circuit may further comprise a photosensitive element responsive to high and low ambient light conditions for cycling operation of the LED. A replaceable electrical power cell is positioned in the housing in the electrical drive circuit as a power source. 
   The terms white light and broad spectrum radiation are used broadly in this patent. The present invention uses LEDs which emit a spectrum blend of visible light on an illuminated surface at a near minimum intensity level which produces a physiological response in a normal human eye. The terms white light and broad spectrum are thus used in the sense of any spectrum output producing greater perceived brightness than monochrome radiation generated at the same energy level. 
   Additional effects, features and advantages will be apparent in the written description that follows. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, further objects and advantages thereof, will best be understood by reference to the following detailed description of illustrative embodiments when read in conjunction with the accompanying drawings, wherein: 
       FIG. 1  is a partial cutaway view of a wireless doorbell transmitter in accord with the invention; 
       FIG. 2  is an alternative wireless doorbell transmitter in a partial cutaway view; 
       FIG. 3  is another alternative wireless doorbell transmitter in a partial cutaway view; 
       FIG. 4  is yet another alternative wireless doorbell transmitter in a partial cutaway view; 
       FIG. 5  is a detailed circuit schematic for the wireless doorbell transmitters of  FIGS. 1–4 ; 
       FIG. 6  is a perspective view in partial cut-a-way of a portable marker luminaire; 
       FIG. 7  is a circuit schematic for the luminaire of  FIG. 6 ; 
       FIG. 8  is perspective view in partial cut-a-way of a driveway marker luminaire; 
       FIG. 9  is a perspective view in partial cut-a-way of an illuminated address sign; 
       FIG. 10  is a circuit schematic for the luminairies of  FIGS. 8 and 9 ; 
       FIG. 11  is a circuit schematic usable with the luminairies of  FIGS. 12 and 13 ; 
       FIG. 12  is a perspective view in partial cut-a-way of coin cell marker luminaire; and 
       FIG. 13  is a perspective view of a light pull chain luminaire. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Due to the nature of the human eye, monochrome LEDs operating at the same efficiency as a broad spectrum or white light LED require substantially more current than do the broad spectrum LEDs to achieve the same perceived brightness level. Since contemporary monochrome super bright LEDs do not exhibit substantially greater efficiencies in light generation compared to broad spectrum LEDs, super bright white LEDs may be operated at a current which is small fraction of the rated current for the diode, and at a lower current than a monochrome LED, and still provide a level of illumination useful as a marker for darkness adjusted vision. At the time this patent was written, broad spectrum LEDs are preferred for the marker applications described herein. However, should technical developments lead to monochrome or limited spectrum LEDs exhibiting much higher efficiencies than white LEDs, than such devices might also produce perceptible light at a lower current than a white LED and come to be preferred for many of these applications. 
   A luminaire used for marking the location of an object need not be particularly bright under circumstances where it can be expected that a person looking for the object will have partially darkness adapted vision. Contemporary, super bright, white LEDs rated at 15 to 20 milliamps can be operated in ranges extending from just below 5 milliamps to a few microamps and produce perceptible light. Extraordinarily long battery life for a luminaire can be achieved at these current levels. Battery life can be further extended by turning the LEDs on and off based on the need for light. For example, an ambient light sensitive control circuit may be used to turn off the luminaire during daylight. Using the low-level white LED approach and a daylight sensor, it is possible to obtain battery life in the range of 1–3 years for some applications using typical small lithium coin cells. 
     FIGS. 1–4  illustrate in a series of cut-a-way views battery operated wireless doorbell transmitters in which an embodiment of the invention is incorporated. In  FIG. 1  a wireless doorbell transmitter  10  comprises a plastic case  12  which in turn encloses a printed circuit board  14 . Printed circuit board  14  mounts circuitry  16  used to transmit an encoded RF signal when a switch  18 , which is positioned directly behind a push-button  20 , is closed by the action of pressing the push-button. Circuitry  16  is further arranged so that the current used to generate the RF signal passes through a light emitting diode (LED)  22  causing it to illuminate, and resulting in visible confirmation that the RF transmission has occurred. The RF transmission current would typically be several milliamps. If the LED  22  is a high efficiency type typically known as Super Bright, the LED will light brightly enough to be easily seen even on a sunlit day. 
   Circuitry  16  includes a cadmium sulfide (CdS) light sensor  24  for causing a low level current to pass through the LED  22  when the ambient light level is below a predetermined threshold. If LED  22  is a super bright type of LED that exhibits high efficiency light generation at low current levels, a “glow-in-the-dark” illumination level can be achieved using a very low LED drive current. The combination of a very low glow-in-the-dark current level and the ability of the CdS light sensor  24  to turn the LED  22  off during the day minimizes the total current required from battery  26  and results in long battery life. Wireless doorbell transmitter  10  emits no light when ambient light is sufficient to allow the unit to be seen without aid, emits a low level of light to mark its location during times of darkness, and emits high intensity light, visible during daylight, in response to use to indicate operation. A single type A23 alkaline cell is sufficient to provide a year or more of service. The small battery size in turn permits use of a case  12  roughly comparable is size to conventional doorbell button cases. 
   A light sensor opening  28  through the bottom portion of case  12  allows ambient light to enter the case and fall on the CdS light sensor  24 . A clear lens can be placed in the light sensor opening  28  if sealing the case  12  is considered desirable. Alternatively, case  12  can be made from a translucent or transparent material that allows a useful amount of ambient light to pass through and fall on the CdS light sensor  24 . 
   LED  22  is positioned very near, or partially within, and optically coupled to, a translucent ring  30 . When activated, either by the switch  18  or the CdS light sensor  24 , LED  22  emits light which is coupled into the ring  30  and produces a glow which surrounds push-button  20 . The translucent material of ring  30  scatters the light and distributes it throughout the ring, which is visible across a broad angle. At night, when the push-button  20  has not been pressed, the ring  30  glows at a low level from light from the LED. A normal eye that has achieved some degree of night adaptation can readily see the ring  30  and identify the push-button  20 . Upon push-button  20  being pressed the ring glows at a second, substantially higher level, indicating that the device is operating. 
     FIG. 2  shows a cut-a-way view of an alternative embodiment, battery operated, wireless doorbell transmitter  40 . Wireless doorbell transmitter  40  is similar to the transmitter shown in  FIG. 1 , except that no glow ring  30  is present and switch  18  has been offset to allow placement of LED  22  directly behind a push-button  34 . Push-button  34  is preferably made from a translucent material diffusing any light emitted by LED  22 . A portion  36  of push-button  34  extends over the switch  18  so that the switch is activated when the push-button is depressed. Case  32  is modified as against the case in  FIG. 1  to eliminate provision for the glow ring  30 . 
   LED  22  is positioned directly behind the translucent push-button  34  in such a manner that the light from the LED will be directed onto the push-button. When activated either by the switch  18  or the CdS light sensor  24 , light from the LED  22  illuminates the push-button  34 . The push-button  34  can be clear, translucent, or faceted. Translucent, or faceted materials, diffuse or refract the light from LED  22  and distribute it about push-button  34 . Even when made of clear materials, the cylindrical shape of button  34  provides sufficient scattering of light to make the button visible across a wide angle. Under low ambient light conditions, when push-button  34  has not been pressed, the push-button glows at a low level illuminated from LED  22 . For push-buttons  34  made from a clear material, light emitted from the LED  22  is directly visible through the push-button. In each case, low level light is visible to a darkness acclimated eye. 
     FIG. 3  is a cut-a-way illustration of yet another embodiment of a battery operated wireless doorbell transmitter  42 . The transmitter is similar to the transmitters shown in  FIGS. 1–2 , except that LED  22  now protrudes through the front of case  36 . Push-button  38  is preferably made of an opaque material and is positioned directly over switch  18 . Transmitter  42  is generally similar to the transmitter described with reference to  FIG. 1 . LED  22  itself includes a semiconductor device embedded in a clear plastic material, which is shaped to provide some light scattering. 
     FIG. 4  is a cut-a-way view of still another embodiment of a battery operated wireless doorbell transmitter  44  incorporating a super bright LED and providing two distinct levels of illumination, one lower level for marking the location of the transmitter under low ambient light conditions and another much higher level for indicating operation of the transmitter. The transmitter  44  is similar to those of  FIGS. 1–3 , however, it incorporates a rectangular push-button  48  and a case  49  modified to incorporate the rectangular push-button. A back light reflector  46  distributes light from LED  22  evenly to the backside of push-button  48 . Light reflector  46  is positioned behind push-button  48  and the LED  22  is positioned below the reflector and oriented to cast light upward toward the light reflector and the push-button in order to illuminate the push-button&#39;s back face. The light pattern created by LED  22  is typically a cone that starts at the tip of the LED and is symmetrical about the LED&#39;s central axis as it expands away from the LED&#39;s tip. This central axis of the cone of light extends parallel to and behind the push-button  48 , aligned with the direction of elongation of the push-button. The light cone expands away from the LED  22 , intersecting the push-button  48  where the light is diffused by the translucent material of the push-button causing the push-button to glow. However, direct illumination from LED  22  is not of uniform intensity since the back surface of the push-button  48  is not a uniform distance from the LED. Much of the light emitted by LED  22  does not directly strike push-button  48  and would not add to the brightness of the push-button without reflector  46  from a wide angle due to the light scattering properties of the push-button. 
   Reflector  46  is preferably arranged and shaped so that much of the light from LED  22  that does not directly strike the push-button  48  will strike the light reflector and be reflected back onto the push-button. This reflected light adds to the brightness of push-button  48  and also reduces the intensity of light variations across the face of the push-button. Light reflector  46  is usually a flat surface, but can also be a curved or angled surface. The shape and angle of the light reflector&#39;s surface can be set in conjunction with the position and angle of the LED  22  to minimize variations in light intensity across the surface of the push-button  48 . At night, when the push-button  48  has not been pressed, the push-button will glow at a low illumination level in response to the light from the LED  22  and reflected off of light reflector  46 . For an eye that has achieved some degree of night adaptation, the illumination level is sufficient that push-button  48  can be readily located. 
     FIG. 5  is a circuit schematic for the wireless doorbell transmitters of  FIGS. 1–4 . Encoder and RF circuitry  58  along with the RF antenna  60  are shown only in block diagram form and can be implemented in a multitude of ways that are well known in the art. Coded signals broadcast by encoder and RF transmitter  58  and antenna  60  are received by a receiver and wireless doorbell chime unit  64  over an antenna  62 . 
   Power is supplied to the illumination control circuitry  16  and to encoder and RF transmitter circuitry  58  from a battery  26 , which preferably comprises a single A23 style alkaline cell. A momentary switch  18  connects, when closed, the encoder and RF transmitter circuitry  58  to battery  26  resulting in an encoded RF transmission. Switch  18 , battery  26 , LED  22 , and encoder and RF transmitter  58  are connected in series. When encoder and RF transmitter  58  is operating, it draws several milliamps and, as a result, LED  22  glows brightly. When momentary switch  18  is open, encoder and RF transmitter  58  are disconnected from the battery  26  to prolong battery life. 
   With momentary switch  18  open, any current flowing through LED  22  must be sunk by a bipolar transistor  52 . Battery  26 , LED  22 , resistor  56  and an NPN bipolar transistor  52  are connected in series. Conduction of the transistor  52  is controlled by a voltage divider circuit connected between the positive and negative terminals of battery  26  and comprising a resistor  54  and the CdS light sensor  24 . The base of transistor  52  is connected to tap the voltage between resistor  54  and the CdS light sensor  24 . 
   CdS light sensor  24  is a light sensitive resistor whose resistance depends inversely on the amount of light that falls on it. When ambient light levels are relatively high, the resistance of the CdS light sensor will be low and the current flowing through resistor  54  will be diverted around the base-emitter junction of transistor  52 . In other words V BE  will be low and transistor  52  will be in cut off. With transistor  52  in cut off, no current flows through LED  22 . During daylight hours, the primary current flow is through resistor  54 , which is chosen to have a resistance on the order of 10 Mohms. This high value resistance limits current drawn from the battery  26  to a minimal level, prolonging the battery&#39;s life. As ambient light levels decrease, the resistance of the CdS light sensor  24  increases, and the base current into transistor  52  likewise increases until transistor  52  begins operating. With transistor  52  conducting, current flows through LED  22  and resistor  56 . A value for resistor  56  is chosen to limit the current to a low level, preferably about 5 micro amperes. 
   LED  22  is of a type commonly known as Super Bright and is further of a type that maintains its light producing efficiency even at very low current levels. In addition, the LED should be of a type that produces relatively white or broad spectrum light, which has a perceived brightness greater than that produced by a monochrome LED of equal intensity. One particular LED that meets these requirements is part number NSPW310BS available from Nichia America Corporation. Even at a very low forward current, this type of LED provides enough illumination to be visible to eyes that are at least partially dark-adapted. 
     FIG. 6  is a cut-a-way perspective view of a battery-operated marker light  66 . Marker light  66  provides low level illumination for one year or more on three AAA alkaline cells forming a battery  68  (one cell is shown). The illumination level is not intended to be useful for photopic vision, but rather to provide a useful illumination level for eyes that have achieved some level of night adaptation. Under these conditions (scotopic vision), enough illumination is provided to clearly mark walls, doorways, or other objects. If the eyes are fully night adjusted, enough illumination is provided to carry out simple tasks without requiring any additional lighting. 
   A plastic case  70  encloses a printed circuit board  72  that contains circuitry  74  which uses a CdS light sensor  76  to turn the marker light  66  on or off in response to ambient light conditions. Plastic case  70  also encloses the batteries  68  that supply power for the circuitry  74  and a super bright LED  78 . The circuitry  74  passes a low level current through the LED  78  when the ambient light level is below a predetermined threshold. If a Super Bright LED of the type that maintains its efficiency at low current levels is used for LED  78 , a “glow-in-the-dark” illumination level can be achieved using very low current levels. Very low current levels, combined with the ability of the CdS light sensor  76  to turn off the LED  78  during the day, minimize the current that is required from the Battery  68 . Battery lifetimes of a year or more can be achieved using three AAA alkaline cells, allowing use of a compact package. 
   A light sensor opening  80  in the front of case  70  allows ambient light to enter the case and fall on the CdS light sensor  76 . A clear lens could be placed in the light sensor opening  80  if an open hole is undesirable. Alternatively, case  70  can be made from a translucent material that allows ambient light to pass through and fall on the CdS light sensor  76 . 
   Case  70  further includes a light reflecting surface positioned behind a translucent lens  84 , which in turn forms a substantial portion of the front of the case. LED  78  is positioned within case  70  above and just behind translucent lens  84 , but forward of light reflecting surface  82 . LED  78  is oriented to cast light downwardly both onto the light reflecting surface as well as directly on the translucent lens  84 . The pattern of light created by LED  78  is typically a cone with its point at the LED&#39;s tip that expands symmetrically about the LED&#39;s central axis in a direction away from the LED. Where the cone of light intersects the translucent lens  84 , the lens scatters the light causing the lens to glow and to become visible from a wide band of viewing angles relative to the case  70 . However, the glow is not of a uniform intensity since the translucent lens  84  has a curved surface and various areas of the lens are at different distances from LED  78 . Much of the light emitted by LED  78  does not directly strike lens  84  and thus does not add directly to the brightness of the lens. 
   Much of the light from the LED  78  that does not directly strike the translucent lens  84  strikes the light reflecting surface  82  and is reflected back onto the lens. Light reflecting surface  82  is illustrated here as being a flat surface. Appropriate shaping and variation of the slope of surface  82 , for example by introducing curves thereto or by changing its angle of repose, can be done to vary the angle of incidence light falling thereon from LED  78  and even the distribution of light. Similarly, local changes to the reflectivity of surface  82  can reduce light intensity variations across the face of the lens  84 , at some loss of efficiency. The shape and angle of the light reflecting surface  82  can be set in conjunction with the position and angle of the LED  78  to minimize variations in light intensity across the surface of the translucent lens  84 . Under low ambient light conditions translucent lens  84  glows in response to the light from LED  78  and from the light reflecting surface  82 . After the eye has achieved some degree of night adaptation, the illumination level is sufficient to be useful as a marker light. 
     FIG. 7  is a circuit schematic for battery powered marker light  66  of  FIG. 6 . Battery  68  preferably comprises 3 AAA cells and is connected into a circuit that controls illumination of LED  78  in response to ambient light levels. Attached in series across the cathode and anode of battery  68  are a resistor  86  and a CdS light sensitive resistor  76 , the resistance of which depends inversely on the level of ambient light. 
   Operation of marker light  66  is light sensitive. When ambient light levels are relatively high, the resistance of the CdS light sensitive resistor  76  is low and current flowing through resistor  86  is diverted around the base-emitter junction of transistor  88 . Transistor  88  remains off and no current flows through LED  78 . Resistor  86  is chosen to have a resistance such that current drawn from battery  68  by circuit paths including the resistor (i.e. the path including resistor  86  and light sensitive resistor  76  and the path formed by resistor  86  and the base to emitter junction of npn transistor  86 ) is extremely low, with the result that battery life is little effected. As the ambient light level decreases, the resistance of the CdS light sensitive resistor  76  increases, increasing the base current of transistor  88 . Transistor  88  turns on and causes current to be sunk at the transistor&#39;s collector. 
   Current sunk at the collector of transistor  88  is drawn through a circuit path formed by LED  78  and resistor  90 . Resistor  90  has a value chosen to limit this current to a low level as required to achieve reasonable battery life, but sufficient to provide illumination for scotopic vision. For a fully charged battery  68 , the initial glow-in-the-dark current is set to about 250 micro amperes, but gradually decreases as battery  68  discharges. LED  78  is of a type commonly known as Super Bright that maintains its light producing efficiency even at very low current levels. In addition, if the LED is of a type that produces relatively white or broad spectrum light, the perceived brightness will be greater than that produced by a monochrome LED of equal intensity. One particular LED that meets these requirements is part number NSPW310BS available from Nichia America Corporation. Even at low forward currents, this type of LED provides enough illumination to be useful for eyes that are at least partially dark-adapted. 
     FIG. 8  is a partial cut-a-way view in perspective of a battery powered driveway marker  92 . The driveway marker provides low levels of illumination for one year or more based on a battery  110  comprising four alkaline D cells. Marker  92  comprises a translucent, light scattering, rigid tube  94  which is mounted on one face of a substantially flat, disk-like base  96 . Extending from the opposite face of base is a positioning spike  98 , which allows the marker to be planted in the ground along a driveway or sidewalk. Tube  94  glows from internally generated light emitted by an LED  100 . A portion or all of tube  94  may be hollow in order to enclose an internal structure that houses the battery  110  and the electronic circuitry needed to control LED  100 . LED  100  is of the type commonly know as super bright and glows visibly at a current as low as 4 or 5 milliamps, which is substantially below the LED&#39;s rated output. Such a current level can be supported by battery  110  for over a year if drawn only at night. Light emitted by LED  100  shines upwardly from the LED&#39;s position in a battery housing cover  102  in the lower portion of tube  94 . The intensity of light at any particular point along the surface of tube  94  is usually insufficient for photopic vision, but is visible to eyes which have adapted to night vision. Under low ambient light conditions (scotopic vision), enough illumination is provided to make tube  92  clearly visible. 
   A battery housing  106  located in the lower portion of the tube  94  encloses battery  110 , a printed circuit board and associated circuitry  104  and a light sensitive resistor  108 . Housing  106  is closed at its upper end by a cover  102 . LED  100  is mounted on the printed circuit board  104  and extends upwardly from housing  106  and through the center of cover  102 . Light sensitive resistor  108  is also mounted on the printed circuit board  104  along with circuitry to control the current supplied to the LED  100 . An opening (not shown) in the housing cover exposes the light sensitive resistor  108  to ambient light conditions reaching the sensor through the tube  94 . The housing cover  102  and housing  106  are cooperatively threaded to allow mounting of the cover to the housing. Contacts within housing  106  and on the bottom of the printed circuit board  104  connect battery  110  to the circuitry on the board. 
   When compared with landscape lights, the driveway marker lights of the present invention exhibit the advantage of being self-contained. As such, installation of the product is very simple. This is especially important because driveway markers are often located at points that are the most remote within the yard from a source of power. Compared with solar products which also eliminate the hassle of wiring installation, this product is not dependent on sunlight to recharge batteries, which is a severe limitation for solar technology and it is also less costly because there are no solar panels, nor rechargeable batteries. 
   An alternative application of the driveway marker electronics is a battery powered address sign  112 , illustrated in  FIG. 9 . Address sign  112  is a flattened rectangular case  119  which has a translucent, light scattering display area  118  forming a portion of a front face of the case and a battery enclosure  122  located over the display area. Within case  119 , both behind and to one side of display area  122 , is an LED  116 . LED  116  is oriented to direct light across the case  119  behind the display area  118 . LED  116  is mounted on a circuit board  114 , which may also be used to support a light sensitive resistor (not shown). Along a back wall of case  119 , opposite the translucent display area  118 , is a reflective surface  120 . Reflective surface  120  provides for a more even distribution of light from LED  116  across the display area  118 . A battery  124  comprising four size D alkaline cells is located in battery enclosure  122 . 
     FIG. 10  is a circuit schematic for driveway marker  92  and suitable for use with address sign  112 . Power is supplied to glow-in-the-dark circuitry by battery  110 . The control circuitry provides two series connected resistors, resistor  126  and light sensitive resistor  108  connected between the cathode of battery  110  and its anode. The base of transistor  128  is connected between resistor  126  and resistor  108 . The CdS light sensitive resistor  108  in effect controls the base current, and thus the conduction state of an npn transistor  128 . The resistance value for resistor  108  depends inversely on the amount of light that falls the resistor/sensor. When ambient light levels are relatively high, the resistance of resistor  108  is low and the current flowing through resistor  126  primarily passes by resistor  108  to ground. When ambient light levels are low, the resistance value of resistor  108  increases, and base current is directed into transistor  128 , driving the transistor into conduction. The resistance value chosen for resistor  126  is high enough, on the order of one megaohm, that the current drawn by any path including resistor  126  is negligible in terms of the current&#39;s effect on battery life. 
   Transistor  128  in turn controls a current source feeding LED  100 . When transistor  128  is conducting, current flows through a pair of series connected diodes  132  and  134 , which connect the base of pnp transistor  136  to the cathode of battery  110 . The current from diode  134  passes further through resistor  130  and from the collector to the emitter of transistor  128 . The forward bias drop across diodes  132  and  134  provides a substantially fixed emitter to base bias for transistor  136  driving the transistor into conduction. Transistor  136 , when on, functions as a current source feeding LED  100 , which is connected by one terminal to the collector of the transistor. A resistor  138  connected between the emitter of transistor  136  and battery  110 , limits the amount of current sourced to a level consistent with long battery life. 
   The value for resistor  138  is chosen to limit this glow-in-the-dark current to a low level as required to achieve reasonable battery life, e.g. about 4 milliamps. LED  100  is of a type commonly known as Super Bright. In addition, if the LED is of a type that produces relatively white light, the perceived brightness will be greater than that produced by a monochrome LED of equal intensity. One particular LED that meets these requirements is part number NSPW315BS available from Nichia America Corporation. This type of LED provides enough illumination to be useful for eyes that are at least partially dark-adapted. Using the low-level white LED approach, it is possible to light the luminaire and still achieve typical battery life of one year or more. In combination with a daylight sensor, battery life can be further extended. 
   For applications where duty cycling as a function of ambient light is undesirable, for example areas which are usually dark absent artificial light, the LED drive circuitry may advantageously be simplified. Referring to  FIG. 11 , a simplified LED  140  drive circuit is taught. A battery  144  comprises a single coin cell to energize super bright LED  140  through a simple series circuit including the cell, a resistor  142  and the LED. The value of resistor  142  is selected so that the current through LED  140  is substantially below the rated value of the LED, as described above for the photo sensitive circuits. Specific component values depend upon the application. 
     FIG. 12  depicts a coin cell marker light  150  which may incorporate either the circuit of  FIG. 11 , or that of either  FIG. 5  or  12 , modified for the lower power application. Where the circuit of  FIG. 11  is used, a single CR2450 lithium cell is used in series with a resistor chosen to limit forward current to about 70 micro amperes and which gradually decreases as the battery discharges. Alternative circuit arrangements, such as that of  FIG. 10 , can be applied which will source current at nearly a steady state value until the battery approaches exhaustion. The LED is preferably a broad spectrum type such as the NSPW315BS supplied by Nichia America Corporation. 
   Coin cell marker light  150  provides a year or more of low level illumination. Coin cell marker light  150  comprises a semi-transparent, faceted, or translucent case top  168  which is roughly bowl shaped and which attaches around the lip of a plate shaped case bottom  162 , allowing the case top to be rotated on the case bottom. Case top  168  operates to scatter light impinging on its interior surface. If an optional light opening  166  is provided and the case bottom  162  is attached to a wall or fixture, case top  168  can be rotated to better position the light opening for directing light to illuminate an object or surface. 
   Mounted within case top  168  is a printed circuit board  156 . Attached to the bottom of the printed circuit board  156 , between the board and the case bottom  162 , are battery cell retainer clips  160 , which are arranged in a semicircle and which are spaced to grasp a coin cell  164  pressed in the semicircle. A resistor  158  is also shown attached to the bottom face of printed circuit board  156 . Mounted above the printed circuit board  156  is a light reflector  154 , and above the light reflector is disposed the LED  152 . LED  152  casts light directly onto the translucent case top  168 , and onto reflector  154 , which reflects scattered light onto the case top. Case top  168  may be colored, playfully shaped, or include an image for projection onto a surface. 
   Referring now to  FIG. 13 , another application of the LED energization circuit of  FIG. 11  is illustrated. Here a super bright LED  172  is fitted within a pull chain grip  170  formed from a decorative case top  178  and a snap on case bottom  180 . Grip  170  hangs from a chain  182 . Fitted into the upper portion of case bottom  180  is a battery cell holder  174 , which also provides an attachment location for the current limiting resistor (shown in  FIG. 11 ) and a coin cell  176 . LED  172  attaches to the bottom of the battery holder  174 . Case bottom  180  may provide light scattering. 
   The invention provides cordless and inexpensive apparata having long battery life for marking the location of objects and enabling them to be found under conditions of darkness. 
   While the invention is shown in only a few of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit and scope of the invention.