PROBLEM TO BE SOLVED:
The introduction of the Solar Garden Light in the mid-80ís heralded in a new market for small photovoltaic solar panels and a potentially large consumer market.
Quite a number of lighting producers manufactured solar garden lights during this period using a variety of Crystalline and Thin-Film solar panels, all using very small incandescent light bulbs.
While the solar garden light was welcomed as a non-hard wired version of traditional "string" lights that used a plug-in transformer and 25-50Ū of copper wire to power the lights, the early versions of solar garden lights fell very short in terms of brightness and night-time ON-time. Additionally, they were very susceptible to corrosion since the circuit boards were not conformal-coated and deteriorated due to rain, salt from snow melting, garden fertilizers and dog urine.
The market steadily grew until the early 90ís when a number of market conditions occurred:
1-As competition increased between the various manufacturers of solar garden lights, the requirement to decrease prices continued to influence the design of the light, notably the size of the solar panel, which was the most expensive part in the solar garden light product.
To properly recharge the internal battery, the solar panel had to be large enough to recharge the energy that was taken from the battery the previous night by the incandescent light bulb. Unfortunately, since the solar panel was the most expensive component in the solar garden light product, the manufacturers had begun decreasing the size of the panel and therefore the power output that could be available to recharge the battery.
This move to a smaller and less costly solar panel was especially apparent in the winter months where high sunlight levels were limited and therefore the panel did not have enough hours of sunlights to properly recharge the battery. This caused substantially shortened On-times and partially recharged batteries which caused battery failures at an increasing rate.
To counter the smaller solar panel and to increase the On-time, the manufacturers turned to smaller incandescent light bulbs, which increased the On-times but also radically decreased the light levels of the already timid bulbs.
2-Consumer confidence in the solar garden light diminished to a level that a number of the manufacturers gave up and went back to traditional wall-transformer "string" lights.
Enter PHOTON TECHNOLOGIES and the Ultra-Bright LED.
In 1995, the Ultra-Bright LED was just being introduced by Hewlett-Packard and had never been used as a high-brightness light source in outdoor lighting, big or small. PHOTON TECHNOLOGIES received several samples of the new HP-HLMP series LED in the only color that was available at the time, amber, and began to experiment with its properties.
Several of the differences in adapting any incandescent bulbed lighting product to LEDís is that LEDís have polarity and incandescent bulbs do not. In other words you have to put Positive power into the Positive leg of the LED and the Negative into the Negative. This is not a requirement for incandescent bulbs.
Of most importance, unlike an incandescent bulb that will only absorb as much power as its filament is rated to use, an LED will absorb as much power as is available to it which will lead to a very quick burning of the internal chip and its destruction.
To decrease the power going to the LED chip, a simple "current limiting resistor" is added to the positive (+) side of the power lead to only allow a pre-specified amount of current to flow to the LED. At the time of the introduction of the HP-HLMP series amber LEDís, the maximum current allowed to flow to these LEDís was about 25 mA at about 2.5 to 3.0 volts. An inexpensive 28 ohm resister solved this problem.
NOTE: Todayís LEDís in a wide variety of colors are rated to absorb a much higher current level, primarily due to "heat-sinking" of the wire leads or the internal chip to allow heat buildup to escape or be dissipated at higher levels of current input.
The third main hurdle to overcome was how to channel the very directional beam of the LED so that it could replicate the normal 360 degree (all-around) spread of the traditional incandescent bulb. LEDís are directional by nature. In other works, all the light comes out of the front of the LED instead of radiating "around" the bulb. This characteristic is similar to the old pen-light light bulbs used as small, spot-type flashlights where the bulb has a small focusing lens built into the bulb.
The LED is the same and focuses all of its light to a small, narrow beam, out the front of the LED. LEDís are available with a variety of "lens" to allow a wider or more narrow beam of light to escape from the front, usually with a wider beam having a lower illumination level (rated in microcandellas).
In the design of the new version of the solar garden light, the first priority was to place the solar panel on the top of the light where it would get the most illumination from the sun. Past solar garden light designs had an angled solar panel which was good "if" you could install the light with the angled solar panel facing the sun "and" the bulb facing the sidewalk, but if your home was not located exactly in the correct angle to the sun, the light beam from the light would be aimed in the wrong directions, so our design placed the solar panel directly on top of the new solar garden light. While this was not the best angle for sun charging during the day, it did allow the light to be placed in any location.
A major change related to the how the light output of the light was how the light was going to be used. Since the actual illumination from any solar lighting device is related to the brightness of the bulb/LED, and since the solar panel had to be small to cut costs, a major shift in product perception by both the consumer and the manufacturer had to be made.
PHOTON TECHNOLOGIES was the very first company to design a solar garden light that used the light output from the fixture as a "delineator" and not a direct beam light source. In other words, the most of the light output would go toward illuminating the fixture and its internal lensing and not attempting to illuminate non-reflective:
In other words, why even make the attempt to illuminate non-reflective surfaces. Our solar garden light, used the light output to illuminate the internal fresnel lens by using the tightly focused LED beam, which was installed in the top of the fixture in what we called a "solar top", downward to a conical shaped mirrorzed reflector which then reflected the radiated light out to a fresnel lens, which then became illuminated in a fairly bright "bulb" like format. While the fresnel lens allowed some of the light to escape to the surrounding ground, most was capture in the fresnel lens which provided the "delineator" effect. This was a new and innovative method to use the minimal LED light output. Illuminate the device, not the surrounding ground.
One of the primary keys to allowing the sharply focused beam of the LED to work with the fresnel lens, was the "mirror zed reflector" which had the function of spreading the LED light beam out to the surrounding fresnel lens. This invention was developed by Robert Mulligan in 1995 during early experiments using the first generation ultra-bright LEDís that had just been introduced by Hewlett-Packard. This innovative method of spreading out the LED beam was developed without the need for extensive optics and reflective research. It came as the result of Mr. Milliganís visit to a local "Party Store" and the purchase of several small chrome plated plastic "champagne" glasses that are used as decorations on wedding cakes.
Simply by removing the stem and the base, the resulting "cup" became a perfect inverted reflective conical shaped surface that could be inserted into the fresnel lens to reflect the LED beam outward to the lens.
Very simple, but very innovative use of an existing product to develop another.
As a result of PHOTON TECHNOLOGIES efforts, the first order for solar garden lights using this design was for 500,000 units, which put the solar garden light back on the map as a useful and effective consumer product and resulted in many spin-off products from other companies.
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