Abstract:
A sunlight measuring device that quantifies the accumulation of light at a particular site. The sunlight measuring device is a battery-operated device mounted on a stake for easy insertion into the ground. The device is placed at the intended site for growing a plant. The light that falls on the sunlight measuring device over a period of time is accumulated and the light accumulation is represented by a visual signal that indicates one of four light conditions: full sun, partial sun, partial shade, full shade.

Description:
BACKGROUND INFORMATION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to the field of devices that measure solar radiation. More specifically, this invention relates to a device that measures the amount of accumulated sunlight that is received at a specific location over a particular period of time.  
         [0003]     2. Description of the Prior Art  
         [0004]     All plants require some level of sunlight in order to grow and thrive. Evolution has created differences in the cell structure of plants and, as a result, different plants require different light conditions to grow. Some plants require full sunlight conditions throughout the day while others thrive in total shade.  
         [0005]     Gardeners and landscapers are well aware of the need to match the light requirements of a plant with the light condition of specific planting site, but often lack the necessary tools to accurately measure accumulated sunlight conditions at the site over a period of time. The information typically provided on the label of a garden plant is very general, and with regard to the light condition required for the plant to thrive, the information is usually indicated only as: full sun, partial sun, partial shade, or full shade. It would be most helpful to gardeners to have a device that provides information about light conditions in terms that correspond to the terms used on the label and used by the general gardening public.  
         [0006]     Sunlight measuring devices are widely available for use by professional photographers and gardeners. Many of these devices make spot measurements of light intensity at an instant in time. This information is of little value to a gardener, who needs to know the accumulated light condition of a particular site throughout the day. Other devices measure accumulated sunlight over a period of time, but provide the information in a form that is difficult for gardeners to evaluate, such as in sols/h and total sols per selected period of time. This requires that the gardener know how to equate the sols/h information with the usual light conditions indicators of full sun, partial sun, etc. that are typical for the garden industry. Still other devices are complicated to use because they require some data input effort on the part of the user.  
         [0007]     What is needed, therefore, is a device that calculates accumulated sunlight over a given period of time at a particular site and presents the sunlight information to the gardener in gardener&#39;s terms that are comparable to the information on the typical plant label.  
       BRIEF SUMMARY OF THE INVENTION  
       [0008]     For reasons cited above, it is an object of this invention to provide a device that accurately measures the amount of accumulated light that falls at a particular site and provides information on the general light condition at that site over a 24 hour period of time. It is a further object to provide such a device that displays the information in terms that relate directly to the sunlight tolerance recommendations provided by nurseries and garden centers on most plant labels.  
         [0009]     The objects are achieved by providing a sunlight measuring device that measures over a period of time the accumulated light that falls on the site in which the device is placed and that provides an indication of the general light condition of that site in gardener&#39;s terms. The sunlight measuring device according to the invention has a sunlight collector lens for funneling light to a light sensor, and four light condition indicators labeled “Full Sun”, “Partial Sun”, “Partial Shade”, and “Full Shade”. The light sensor collects available sunlight/solar radiation and converts the energy from the light into an electronic signal (voltage or current) in direct proportion to the intensity and duration of the light received by the sensor. A microprocessor calculates an accumulated light value based on the accumulated magnitude of the signal from the light sensor, compares the accumulated light value with four light thresholds that correspond to the four light conditions full sun, partial sun, partial shade, and full shade, and, as a function of the light threshold reached, activates the corresponding light condition indicator.  
         [0010]     The sunlight measuring device according to the invention measures for a predetermined period of time, typically, a period of 24 hours. Ideally, the device is used on a day with continual sunshine throughout the day. When initially turned on, each of the light condition indicators is sequentially activated, to indicate to the user that the unit is turned on and functioning properly. The sunlight measuring device samples sunlight and accumulates data for an initial accumulation period of time. It then processes the data to determine how much total light has accumulated and compares the total light to predetermined light thresholds, to determine which light threshold has been reached. It then activates the light condition indicator of the corresponding light threshold. The initial accumulation period is typically 12 hours. The sunlight measuring device stops accumulating data after the predetermined time period, but the light condition indicator remains activated, so the user can see the results. If the device is left on beyond the predetermined time period, it shuts off completely after a shut-off period has lapsed, to conserve power. This shut-off period may lapse 24 or 36 hours, for example, after the initial power up of the device. The accumulated light data is retained in memory. The last threshold level that was achieved is ascertainable by pressing the on/off button, which again activates the particular light condition indicator that corresponds to that threshold level.  
         [0011]     The sunlight measuring device filters the light, in order to isolate, record, and accumulate only photosynthetically active radiation (PAR) at wavelengths of 400 nm to 700 nm. This is because only photons in the PAR region of the color spectrum are active in creating photosynthesis.  
         [0012]     The sunlight measuring device may be used indoors or outdoors. The most accurate measurement of outdoor light conditions is obtained by measuring at least eight hours of daylight on a sunny day. The sunlight measuring device may have various mounting means, depending on its intended use. For measuring outdoor light conditions in a garden, for example, the sunlight measuring device is ideally mounted on a stake that is insertable into the ground or into a flower pot filled with soil, with the sunlight collector lens pointing at the location of the noonday sun.  
         [0013]     The sunlight measuring device according to the invention may also be used for many other purposes, and is not limited to use for determining the light conditions for growing plants. For example, a user may wear the sunlight measuring device for a period of time, as a pendant around the neck or pinned to clothing, to determine the amount of light the user is exposed to during the day. This may be useful in adjusting light conditions for a person suffering from seasonal adjusted disorder. The legends on the sunlight measuring device that explain the meanings of the individual light condition indicators may be adapted according to the use. For example, rather than “full sun”, “partial sun”, etc., the legends may use terms, such as, “abundant light”, “average light”, “low light”, and “insufficient light,” or other terms that are meaningful for the particular application. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     The present invention is described with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. The drawings are not drawn to scale.  
         [0015]      FIG. 1  is an exploded view of the internal components of the sunlight measuring device.  
         [0016]      FIG. 2  is a circuit diagram of the sunlight measuring device according to the invention.  
         [0017]      FIG. 3A  is a plane view of a first side of the printed circuit board.  
         [0018]      FIG. 3B  is a plane view of a second side of the printed circuit board.  
         [0019]      FIG. 4  is a top plane view of the sunlight measuring device, showing the sunlight display panel with the four sunlight categories.  
         [0020]      FIG. 5  is an elevational view of the sunlight measuring device.  
         [0021]      FIG. 6 a  cross-sectional view of the sunlight measuring device, showing the placement of the inner components within the base. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]      FIG. 1  shows the exploded assembly view of a sunlight measuring device  100  according to the invention, comprising a sunlight display panel  20 , a sunlight measurement means  30 , and a base  50 .  
         [0023]     The sunlight display panel  20  comprises a faceplate  22 , a protective lens  26  that includes a sunlight collector lens  24  that allows sunlight to pass through to the sunlight measurement means  30 , and four light condition indicators  25 , which include a full sun indicator  25 A, a partial sun indicator  25 B, a partial shade indicator  25 C, and a full shade indicator  25 D. The sunlight display panel  20  is securely attached to the base  50 , which together form a housing  10  for the sunlight measurement means  30 , which includes a light filter  36  and a printed circuit board  34  mounted on a chassis  32  and a power source  35 .  
         [0024]      FIG. 2  is a schematic diagram of the electronic components of the sunlight measuring device  100 .  FIGS. 3A and 3B  show the layout of the printed circuit board  34  and the various components mounted thereon. The printed circuit board  34  includes a light sensor  40 , which collects sunlight and converts it into an electrical signal, the strength of the signal being in direct proportion to the intensity of the light falling on the face of the light sensor  40 . The light sensor  40  may be a photoreceptive diode, such as manufactured by Texas Advanced Optoeletronic Solutions.  
         [0025]      FIG. 3A  shows a first side  34 A and  FIG. 3B  shows a second side  34 B of the printed circuit board  34 . The light condition indicators  25 , a programmable microchip V 1 , the light sensor  40 , as well as electronic resistors, capacitors, and other circuitry components are shown mounted on the first side  34 A. A retaining means  35 A for holding the power source  35  is provided on the rear side  34 B, as well as electrical contacts  38 A for the on/off switch  38 . A through-hole  34 C through the printed circuit card  34  is used to mount the card to the chassis  32 .  
         [0026]     In the embodiment shown in the drawings, the four light condition indicators  25 A- 25 D are light-emitting diodes. It is not intended, however, that this invention be limited to the use of light-emitting diodes to indicate the particular threshold of accumulated light achieved. Other suitable indicators include an analog display with a scale and needle, a color-changing window, or a bar that varies in height to indicate the level of accumulated light. The power source  35  provides power to the printed circuit board  34 . Any suitable conventional battery, such as a rechargeable battery, a solar-powered battery, or conventional, non-rechargeable battery may be used as the power source  35 . In the embodiment shown, a 3 volt lithium coin cell is used.  
         [0027]     The chassis  32  and the power source  35  are mounted in the base  50 . A translucent area  37  is provided on the chassis  32  for passing light from the sunlight collector lens  24  through to the light sensor  40 . This translucent area  37  may be a clearly defined area on the chassis or the chassis may be molded from a translucent plastic that allows light to pass through it. The chassis  32  provides compressive stress protection to the circuit board  34 . It also provides individual light separation for the four light condition indicators  25 A- 25 D by means of four tunnels or apertures  32 A- 32 D that prevent the illumination from one light condition indicator from causing a neighboring light condition indicator to appear illuminated. The chassis  32  may be compounded with a die comparable to that of the light filter  36  to block light waves outside of PAR range. Because the sun travels in an arc through the sky throughout the day, sunlight strikes and passes through the sunlight collector lens  24  to the light sensor  40  at varying angles throughout the day. The sunlight collector lens  24  has a dome shape, which effectively increases the surface that is illuminated by the rays of the sun as it travels throughout its arc, as the earth rotates through the day. The light from rays that are perpendicular to the curved surface of the dome are collected and measured by the sunlight collector lens  24 . Thus, the lens collects and measures sunlight throughout the sunlight hours, not just when the sun is high overhead. This results in a more consistent illumination of the interior surface of the sunlight collector lens  24  than would be the case if the sunlight collector lens  24  were flat.  
         [0028]     A light filter  36  is placed between the translucent area  37  on the chassis  32  and the sunlight collector lens  24 . A suitable filter is a commercially available film in a very specific magenta color range that selectively passes only photosynthetically active radiation (PAR). The magenta filter is manufactured by Lee Filters and is a mylar/plastic film in the color #039 “Pink Carnation”. Instead of providing a separate light filter component, it is also possible to allow the sunlight collector lens  24  or the translucent area  37  to perform the function of the light filter  36  by tinting the sunlight collector lens or translucent area  37  to the particular magenta color that matches the blockage range of the light filter  36 .  
         [0029]     The interior of the sunlight collector lens  24  passes light through to the translucent area  37 . The light is diffused by the dome shape of the sunlight collector lens  24  and illuminates the translucent area  37  on the chassis  32 . The sunlight collector lens  24 , the light filter  36 , and the translucent area  37  cooperate to diffuse the incoming light over the translucent area  37  and also effectively reduce the total amount of sunlight passed through to the light sensor  40 , thereby decreasing the effect of the variation in the intensity of the sunlight throughout the day. The light sensor  40 , mounted on the printed circuit board  34 , senses the illumination on the underside of the chassis  32  in the translucent area  37 . The sensor  40  and the operating program in the microchip V 1  combined have a threshold that distinguishes between the illumination from direct sunlight falling on the lens  24  and decreased illumination from ambient light falling on the lens  24  when the sunlight measuring device  100  is in a shaded condition.  
         [0030]      FIG. 4  is a top plane view of the sunlight display panel  20 . Referring also to  FIG. 1 , the faceplate  22  contains legends that explain the meanings of the light condition indicators  25 A- 25 D that differentiate the four light conditions. The faceplate  22  is preferably made from a clear film material such as mylar, with a clear adhesive on the reverse surface. In the particular embodiment shown, the faceplate  22  is assembled over the protective lens  26  and has a first cut-away area above the sunlight collector lens  24  and four clear areas above the four light condition indicators  25 A- 25 D. The sunlight collector lens  24  protrudes through a cut-out in the faceplate  22 . Illumination from the four light condition indicators  25 A- 25 D is visible through the four clear areas. Rather than using a separate faceplate, it is also possible to provide legends that are etched or otherwise provided directly on the protective lens  26 .  
         [0031]      FIG. 5  is an elevational view of the sunlight measurement means  100  according to the invention and  FIG. 6  is a partial cross-sectional view, showing the arrangement of the various components within the housing  10 , which is formed by the sunlight display panel  20  and the base  50 . A seal means  28 , such as an O-ring made of a compressive rubber or synthetic rubber material, may be used to provide a water-tight seal between the base  50  and the sunlight display panel  20 . An installation means  60  may be attached to the base  50 . In the embodiment shown, the installation means is a stake  63  for mounting the sunlight measuring device  100  in the ground and has a threaded area  64  at the top for fastening to the base  50 . Another suitable installation means  60  may be an adhesive backing for mounting the sunlight measuring device  100  on a rigid surface.  
         [0032]     In the embodiment shown, the chassis  32 , the printed circuit board  34 , the protective lens  26 , and the faceplate  22  are held together within the housing  10  by means of screws that pass through through-bores in the base  50  and thread themselves into hollow posts in the underside of the protective lens  26 . The printed circuit board  34  and the faceplate  22  have cut-outs that fit around the threaded fasteners, thereby maintaining these elements in the proper orientation within the housing  10 .  
         [0033]     A washer  12  may placed between the underside of the printed circuit board  34  and the on/off switch  38  to provide waterproofing, cushioning and resistance to closing of the metal momentary dome switch on the underside of printed circuit board  6 . The washer may be made of a rubber foam material. The on/off switch  38  protrudes out through the base  50  and when pushed upward contacts a metal dome switch  38 A on the printed circuit board  34  to switch the sunlight measuring device  100  on or off.  
         [0034]     A microprocessor  42  is mounted on the printed circuit board  34 . The microprocessor  42  is a factory programmable microchip V 1 , such as the chip PIC-16F630-1/st produced by Microchip Technologies, Inc, Chandler, Ariz., and contains an algorithm that accumulates the electrical signal over the predetermined period and an internal clock set for a maximum time that corresponds to a predetermined period, which is typically 24 hours. The algorithm has thresholds for the accumulated signal, each threshold corresponding to one of the light condition indicators  25 A- 25 D. When enough light is accumulated to reach a particular threshold, the light condition indicator  25  corresponding to that particular threshold is illuminated. In the embodiment shown, the light condition indicators  25  include: full shade indicator  25 D, partial shad indicator  25 C, partial sun indicator  25 B, and full sun indicator  25 A. The power source  35  provides the power for the electronic components.  
         [0035]     Operation: Power is applied by pressing the on/off switch  35 . At initial power up, the four light condition indicators  25 A- 25 D light up sequentially until the microprocessor  46  has stabilized. All four light condition indicators  25 A- 25 D flash for a few seconds, for example, once every 2 seconds, indicating that sunlight accumulation is in progress. Once the light sensor  40  has accumulated data for a predetermined accumulation period, for example, 12 hours, the single light condition indicator corresponding to the threshold of the accumulated sunlight flashes for a few seconds and remains illuminated thereafter, for a predetermined information period, such as, for 12 or 24 hours. During this information period, the light condition indicator may be set to flash every couple of seconds, or may be continuously illuminated. At the end of the accumulation period, the sunlight measuring device  100  ceases to accumulate light. In one embodiment, the sunlight measuring device  100  is programmed to have an accumulation period of 12 hours, an information period of an additional 12 hours, and to shut off at the end of the information period. It is, of course, possible, to provide the sunlight measuring device  100  according to the invention with an accumulation period of 24 hours and an information period of an additional 12 hours. The programmable microchip V 1  may also be programmed to activate the corresponding light condition indicator  25  after an initial accumulation period, while the device is still in the process of accumulating light. At the end of the information period, for example, the sunlight measuring device  100  shuts off. No further indication of activity is shown. If the on/off switch  38  is pressed again, the last threshold of accumulated light is displayed by one of the four light condition indicators  25 A- 25 D lighting up.  
         [0036]     Described and illustrated herein is an sunlight measuring device to record and quantify, in generally accepted gardening terms, the amount of accumulated sunlight that falls on a specific site during a predetermined period. The sunlight measuring device is intended to aid gardeners and landscapers by helping them accurately place plants according to their physical light requirements.  
         [0037]     It is understood that the embodiments described herein are merely illustrative of the present invention. It will therefore be appreciated by those skilled in the art, that the sunlight measuring device according to the invention may be used for other purposes than determining light conditions for gardening purposes, and that other modifications may be made to the present invention without deviating from its spirit and the scope as defined by the following claims.