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FIELD OF THE INVENTION:
The invention relates to solar powered elective lighting in general and to
illumination of streets by LED based solar lights in particular.
BACKGROUND AND PRIOR ART:
Solar powered street lights are known in prior art. Such street lights have
typically one 11 watt CFL (compact fluorescent lamp) as the light source. As
generation and storage of solar electricity is relatively very costly, constant
efforts were made to reduce the power consumption of the light source.
Although LED have been tried successfully in domestic lighting and for low level
illumination, an LED based luminaire suitable for street lights was typically rated
at 20 watts so far, which made such street lights expensive, as bigger solar
module as well as battery were needed. Battery size contributes greatly to the
total weight of the street light as the battery is housed in a battery box which is
mounted on the pole of the street light.
The present invention seeks to overcome these drawbacks of the prior art.
OBJECTS OF THE INVENTION:
An object of the invention is to provide LED based luminaire suitable for solar
powered street lights that have low power consumption
Another object of the invention is to provide solar street lights that have smaller
solar modules.
Yet another object of the invention is to provide solar street lights with smaller
battery size.
A further object of the invention is to reduce the weight of a solar street light
A stili further object is to reduce the cost of a solar street light and increase life
of the luminaire

DESCRIPTION OF THE INVENTION:
A solar street light in the prior art requires a 70-watt solar module and a 12-volt
65 to 80 Ah lead acid battery to power an 11-watt CFL based lummaire for dusk
to dawn operation. According to the invention, with the current available
performance of LEDs and a proper design of the lummaire and its electronics, a
LED lamp of 6 watts can replace an 11-watt CFL providing same level of
illumination. With 6 watt LED lamp, a 36-watt solar module with a 12 volt 40 Ah
capacity battery is sufficient for dusk to dawn operation of the street light,
thereby reducing the cost of the light significantly. The recurring expenditure on
the battery replacement will also reduce due to the requirement of lower
capacity battery in the case of LED based light. Also as the LED's life is expected
to be about 50000 to 100000 hrs of illumination, the LED lamps will run without
maintenance for longer durations (a serious maintenance problem for the street
lights with CFLs).
According to the invention, the LED based street light lummaire is made with
special care on its light output and energy consumption
Ultra bright narrow angle white LEDs of low power can be arranged in series and
parallel configuration to suit the voltage of the system. A voltage control circuit is
required to prevent the excess flow of current to the LEDs. Alternately, ultra. N
bright wide angle high power white LEDs can be used to cover illumination in a
larger area. However, the confinement of light to a particular area is better in
narrower angle LEDs and the fraction of light escaping to the surroundings or to
the sky is also reduced in the case of narrow (~20 degree) angle LEDs. The
lummaire is made plane if small area illumination is required and convex if large
area illumination is required. The convex angle of the LED mounted plate can be
varied from 0 to 20 degrees from the tangent on the center point of the plate to
get variable area illumination. For covering larger areas, wide angle high power

LEDs are used. With these features, a streetlight has been devised which
consumes much less energy for its operation.
The invention will be described in detail with the help of the accompanying
drawings. An exemplary embodiment of the invention is described, but there can
be several other embodiments of the invention, all of which are deemed covered
by this description.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Fig: 1 shows an LED based solar street light in accordance with the invention.
Fig: 2 shows the schematic of the solar street light.
The streetlight according to the invention has a lummaire (1.1) which has a
cluster of either narrow angle LEDs of low power of about 0.1 watt each or wide
angle LEDs of about 1-watt each. The LEDs are connected in series and parallel
combination to provide uniform illumination on the required area on the street or
pavement. -
The lummaire has been made convex to cover a 2.5m diameter area. The angle
of the LED mounted plate has been kept around 10 degress from the tangent to„
the center point.
A sealed maintenance free battery (2.1) of 12 Volt, 40 AH is installed in a battery
box (1.3). The battery of the street light is charged with a crystalline silicon solar
module (1.2) Alternatively amorphous silicon based or other thin based solar
module can also Be used. The module is mounted facing south on the top of the
street pole and the angle of the module is kept at the latitude angle of the place
where the street light is installed

A specially designed circuit is installed in the luminaire/ battery box. The circuit
has a charge controller (2.2), pulsing and dusk to dawn control circuit (2.3) with
switch. The circuit is powered by the battery and consumes very little power.
The mounting arrangement is show in fig. 1. All components of the light are
installed on a pole (1.4), which is grouted up to the required depth in the
ground. The schematic of the operation of the light is shown in fig. 2. The solar
module (1.2) charges the battery of the street light during the daytime through a
charge controller (2.2). There are various set points and indications in the
charge controller to display and control overcharging and over discharging of the
battery, so that the battery does not get damaged. The glowing hours of the LED
Luminaire is controlled automatically by dusk to dawn control circuit (2.3) which
switches the luminaire on at dusk and off at dawn without any human
intervention

WE CLAIM:
1 An LED based solar street light comprising a luminaire (1 1), a solar module
(1 2), battery box (1 3) containing battery (2 1), charge controller (2 2) and dusk
to dawn Controller with switch (2.3), characterized in that the luminaire has a
power rating of about 6 W wherein the narrow angle LEDs are mounted on plate
for covering smaller areas with intense light
2 An LED based solar street light as claimed in claim 1, wherein the luminaire (1.1)
has a cluster of LEDs of either narrow angle type or wide angle type.
3 An LED based solar street light as claimed in claim 1, wherein the luminaire (1.1)
has an LED mounted plate which is either convex or flat
4 An LED based solar street light as claimed in claim 1, wherein the convex angle
of said LED mounted plate can be varied between 5 to 20 degrees from the
tangent on the center point of the plate to get variable area illumination.
5 An LED based solar street light as claimed in claim 1, wherein the luminaire (1.1)
has a special LED driver circuit with voltage regulation.

ABSTRACT

LED BASED SOLAR STREET LIGHT
An LED based solar street light comprising a luminaire (1.1), a solar module (1.2),
battery box (1.3) containing battery (2.1), charge Controller (2.2) and dusk to dawn
controller with switch (2.3), characterized in that the luminaire has a power rating of
about 6 W.