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Patent: To Discern Objects In A Well-Lighted, Well-Contrasted Place
Patent:  To Discern Objects In A Well-Lighted, Well-Contrasted Place | aust_txbz, Karl A. Burkett, patent, 8136969, variable lighting, night visibility, night vision, traffic,

Karl A. Burkett of Austin recently received U.S. Patent 8,136,969 for “Variable Lighting System for Optimizing Night Visibility.”

Texas Business Patent of the Day: It's so much not the amount of light, but the types and angles of light that allow you to distinguish objects at night.  A Texas man devised a way to vary lighting at night due to approaching objects, weather or time of night.  

Karl A. Burkett of Austin recently received U.S. Patent 8,136,969 for “Variable Lighting System for Optimizing Night Visibility.”

Burkett applied for the patent more than three years ago on September 17, 2008.

His invention generally relates to lighting systems, according to the patent document. Particularly, the invention relates to lighting systems for optimizing night visibility. 

Night visibility is a well known concern of many individuals and is particularly a safety concern for night driving.

 As a result, artificial lighting such as street lights have been placed on roadways and in parking lots to improve night visibility for motorists.

However, artificial lighting is not always sufficient for motorists and individuals so alternatives for improving night visibility have been established. 

For example, one method for designing fixed roadway lighting promulgated by the American Standards Institute (ANSI) and Illuminating Engineering Society of North America (IESNA) is termed "Small Target Visibility" and is a method for maximizing the visibility of small (7 inch square) targets on a roadway. However, with this method all objects are still not detectable because there is not enough contrast between the object and background. 

Burkett decided to address the desire to optimize headlamp and fixed roadway lighting system interactions to improve visibility. Other systems include aesthetic "under vehicle" lighting as well as variably aimed headlamps wherein both provide some assistance in detecting roadway hazards.

 These existing lighting systems, while beneficial, use large amounts of power and hence are costly. There is a need for a lighting system that further improves visibility at night on roadways and other artificially lit areas while also being cost effective. 

Burkett’s invention solves that problem by providing a variable lighting system ("VLS") for optimizing object visibility at night. The VLS varies the intensity of the variable lighting element to improve the contrast of objects. Contrast or luminance contrast is the relationship between the luminance of a brighter area of interest and that of an adjacent darker area.

Mathematically, it is known as the Weber Contrast and is defined as the absolute value of difference between the two luminances divided by the lower luminance or |(Lo-Lb)/Lb|, with Lo typically representing the luminance of objects and Lb typically representing the luminance of the background. 

Contrast sensitivity is the ability to discern between luminosities of different levels in a static image. Contrast sensitivity varies between individuals, maxing out at approximately 20 years of age, and at spatial frequencies of about 2-5 cycles/degree.

In addition it can decline with age and other factors such as cataracts and diabetic retinopathy. A Contrast Threshold is the minimal amount of contrast, or difference between two shades of objects, needed in order to detect a pattern. Contrast threshold is measured by the number of photons a light stripe reflects in comparison to the number of photons reflected in a dark stripe. The contrast threshold is used to find the contrast sensitivity function, which is defined by taking the reciprocal of the contrast threshold. 

In the prior art relative to fix roadway lighting, the contrast of the target and background is established by geometric factors does not change. Thus if an object is below the contrast threshold it will stay in the non-contrast threshold and be non-visible. For example, for a first certain location, such as between two light poles Lb, may be 1 candela/meter^2 while at a second location the background luminance may be 5 candela/meter^2. In the prior art, the intensity of the illumination on the object and the background is relatively constant and therefore, the contrast is relatively constant. Hence, the contrast may be acceptable for the first location but not for the second location. In the prior art, as a vehicle drives on a roadway with light poles, the vehicle is continually driving though positive contrast and negative contrast areas. 

The VLS varies the intensity of the illumination on the object and background to vary the luminance of the object Lo and the background Lb so that the maximum available contrast for a person with average contrast sensitivity can be obtained at some point in the variable illumination cycle.

The VLS comprises a variable lighting element, and a master synchronizer for synchronizing the timing and sequence of the variable lighting. The variable lighting element cycles through a range of lighting intensities so that any objects illuminated by the variable lighting element and the background will have a variable luminance. The luminance of the object, Lo, and the background Lb are varied such that a contrast above threshold can be obtained at every location along a roadway. It is understood that as the luminance is varied, an contrast below threshold may be obtained and the transition from the maximum contrast to the minimum contrast and the frequency of the maximum contrast (or minimum contrast) will depend on frequency that the intensity of the illumination varies.

The contrast may be positive contrast where the Lo is greater than Lb or the contrast may be negative contrast where Lb is greater than Lo. 

In one embodiment, a VLS is on two or more lighting fixtures such as light poles, street lamps, or indoor lighting and the varying intensity of the illumination from each VLS is synchronized to produce a maximum Weber Contrast. For example, a first VLS may have a high lighting intensity in the north direction and a second VLS may have a low lighting intensity in the south direction. Looking north, any objects illuminated by the first VLS would have a relatively high luminance Lo and the background luminance Lb from the second VLS would be relatively low thereby producing a relatively high Weber Contrast. Then each VLS cycles through a range of lighting intensities such that the first VLS may have a low lighting intensity in the north direction while the second VLS has a high lighting intensity in the south direction. Again looking north, any objects illuminated by the first VLS would have a relatively low luminance Lo and the background luminance Lb would be relatively high. Therefore, using the contrast formula |(Lo-Lb)/Lb| the contrast would be relatively high. 

In another embodiment, a VLS is on one or more lighting fixtures and vehicle contains a non-varying illumination source wherein the varying intensity of the illumination from each VLS is synchronized to product a maximum Weber Contrast. For example, as the vehicle is traveling north, the illumination source on the vehicle has a relatively high lighting intensity in the north direction so any objects would have a relatively high luminance Lo. The closest VLS on a lighting fixture would have a low lighting intensity in the south direction to produce a relatively low background luminance Lb and thereby produce a relatively high Weber Contrast. 

Also, the closest VLS may have a low lighting intensity in the north direction while a second VLS north of the closest VLS to the vehicle would have a high lighting intensity in the south direction. The second VLS north of the closest VLS to the vehicle would be beyond the illumination range of the illumination source on the vehicle so any objects illuminated by the closest VLS would have a relatively low luminance Lo and the background luminance Lb produced by the second VLS north of the closest VLS to the vehicle would be relatively high. Then, to prevent a wash out, or the background luminance Lb matching the object luminance Lo, as the vehicle travels north and the illumination range of the illumination source on the vehicle approaches the second VLS, the lighting intensity in the south direction of the second VLS would decrease as the lighting intensity in the north direction would increase from the illumination source of the vehicle. In one embodiment, the vehicle contains a VLS and the VLS on the vehicle is synchronized with each VLS on the lighting fixture to produce a high Weber Contrast. 

In another embodiment, at least one VLS is on a vehicle and as the vehicle travels, the intensity of the illumination is varied to obtain a maximum Weber Contrast. The vehicle with the VLS may contain a sensor that determines the luminance of the background and adjusts the intensity of the illumination from the VLS to obtain a maximum Weber Contrast. For example, if the vehicle is traveling north and the background luminance Lb is relatively low, then the illumination from the VLS on the vehicle would be relatively high such that any objects within the illumination range of the VLS would have a relatively high object luminance Lo thereby producing a relatively high Weber Contrast. Then, as the vehicle travels into an area where the background luminance Lb is relatively high, the illumination from the VLS on the vehicle would be relatively low such that any objects within the illumination range of the VLS would have a relatively low object luminance Lo thereby producing a relatively high Weber Contrast. 

In one embodiment, the VLS varies the intensity and the color of the illumination on the object to vary the intensity and color of the luminance of the object Lo as well as the intensity and color of the background such that the maximum available contrast for a person with average contrast sensitivity can be obtained. In existing lighting systems, neither color or intensity changes and object luminance Lo and background luminance Lb remain constant and therefore the contrast does not change. If an object is in the non-visible region, it will stay in the non-visible region. 

When color is added, the Weber Contrast formula becomes modified such that the contrast is now defined as |(Lo-Lb)/Lb|+the color contrast metric. The color contrast metric is difficult to quantify because the discriminability of pairs of colors depends on their differences in chrominance and luminance. While an entirely satisfactory metric does not exist that combines these attributes into a single assessment of total color difference, an estimate can be derived by calculating the weighted difference between the locations of the colors in the 1976 CIE UCS (CIE UCS L*u*v*). In addition, the specification of small color differences should be treated with caution due to the inherent lack of color uniformity on most devices.


In one embodiment, the system changes color and light intensity thereby providing a color contrast in addition to the Weber Contrast. The variation of intensity and color is designed to be quick enough to allow detection and reaction yet slow enough to be visually discrete to move the target into the visible range. In one embodiment, the variation is at least every 0.6 seconds. 

In another embodiment, the VLS varies light intensity, color, and direction and optionally includes a detector for detecting motion, noise, or other occurrences. The VLS can be implemented as a fixed lighting source, a movable lighting source, or a vehicle mounted lighting source. The VLS improves visibility at night for all viewers, particularly bicycle riders, pedestrians, and motorists thereby reducing accidents and damage costs and saving lives. Furthermore when compared to known lighting systems, the VLS saves energy, improves the environment, and enhances quality of life by reducing light pollution and light trespass.