GB2382868A

GB2382868A - A lighting strip

Info

Publication number: GB2382868A
Application number: GB0227456A
Authority: GB
Inventors: Peter Norman Langmead; Raymond Osborne
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-12-05
Filing date: 2001-12-05
Publication date: 2003-06-11
Anticipated expiration: 2021-12-05
Also published as: GB2382867B; GB0129157D0; GB2382867A; GB0227456D0; GB2382868B

Abstract

A method of operating a lighting strip 12 that comprises at least three elongate conductors 14, 16, 18 spaced apart from one another 20, 22, and a plurality of light producing devices 24, preferably LEDs, each connected to two of the at least three elongate conductors. The light producing devices and conductors are preferably encased in an insulating material 12 that is at least in part transparent or translucent. At least one controlled voltage source is supplied and may be provided at each end of the lighting strip being selectively connectable to each of the conductors, and may operate the light producing devices by a pulsed voltage or a steady voltage. The lighting strip may also be provided with a system driver for operating the light producing devices in a variety of pre-determined sequences.

Description

- 1 A LIGHTING STRIP

The present invention relates generally to conductive strips on which are mounted electrical 5 components and particularly to a conductive lighting strip utilising light emitting diodes (LEDs).

LED strips are commonly used to provide visual pathways in unlit areas. Examples include emergency 10 pathway markers in aircraft and ships, exit door indicators and ornamental lighting arrangements. LED light strips have a number of advantages over those using electric filament type lamps. LEDs have lower operating temperatures, are relatively cheap to 15 manufacture, are relatively easy to install and have a longer life than conventional lamps or bulbs.

An existing LED strip is disclosed in WO 98/23896 which describes a low profile, rigid or flexible 20 conducting strip capable of being made in long lengths using a continuous manufacturing technique, e.g. extrusion. The disclosed device comprises two or more conducting bars to which are connected LEDs, preferably by use of surface mounting techniques.

25 These LEDs are capable of both static operation, i.e. ON/OFF, and dynamic operation, i.e. running in sequences. However, because the conductive strip is made up 30 of repetitions of a shorter circuit it is only possible to divide the strip at the interface between one complete circuit and the next. The strip cannot be cut to any length which is not an exact multiple of the circuit length if it is to operate correctly. In 35 order to make the manufacture of these strips economically viable the circuit length is usually around 750mm in length.

- 2 - Furthermore, the arrangement of LEDs mounted on the strip can not easily be altered. Removal of an 5 LED breaks the circuit and therefore, to function correctly, if an LED is removed some kind of bridging component must be substituted to complete the circuit.

In addition, due to the complexity of the circuit it is not possible to operate the LEDs in a number of 10 different sequences.

Thus, a lighting strip which can be divided at shorter intervals and with increased functionality is desired. Accordingly the present invention provides a lighting strip comprising at least three elongate conductors spaced apart from one another by a clearance configured in an undulating form, and a 20 plurality of light producing devices, each connected to two of the at least three conductors, wherein the light producing devices are located at a peak or trough of an undulation.

25 Advantageously, the spacing between adjacent light producing devices is equal to a half of the period of the undulation or odd multiples thereof.

The light producing devices are typically LEDs.

The light producing devices and conductors are preferably encased in an insulating material that is at least partially transparent or translucent.

35 The lighting strip preferably includes at least one system driver, which is a controlled voltage source.

- 3 - Preferably a system driver is provided at each end of the lighting strip and is selectively connectable to each of the elongate conductors.

5 Advantageously, the light producing devices are arranged in pairs and each pair is biassed in an opposite direction to adjacent pairs.

The or each system driver may be configured to 10 operate the light producing devices by a pulsed voltage. In particular, the or each system driver may be configured to maintain a first voltage across the 15 light producing devices which is below a threshold voltage required to operate the light producing devices, and to supply pulses of a second voltage sufficient, in combination with the first voltage, to exceed the threshold and thereby operate the light 20 producing devices.

Alternatively, the or each system driver is configured to maintain a steady state voltage sufficient to operate the light producing devices.

Preferably the or each system driver is configured to monitor the condition of the lighting strip. 30 The present invention also provides a method of operating a lighting strip of the aforementioned type wherein the method comprises supplying a series of voltage pulses to operate the light producing devices.

35 The method may further comprise the step of maintaining a first voltage across the light producing devices which is below a threshold voltage required to

- 4 - operate the light producing devices, and supplying pulses of a second voltage sufficient, in combination with the first voltage, to exceed the threshold and thereby operate the light producing devices.

Furthermore, the method may include the step of providing a system driver at each end of the lighting strip which is connected to each of the elongate conductors and selectively controlling the system 10 drivers so as to operate the light producing devices in a variety of pre-determined sequences.

An example of a lighting strip constructed in accordance with the present invention will now be 15 described with reference to the accompanying drawings, in which: Figure 1 is a schematic plan view of a first embodiment of the present invention; and Figure 2 is a perspective crosssection view of the lighting strip of Figure 1 through line 2-2, with part of the outer protective layer removed for clarity. The lighting strip as shown in Fig. 1 comprises circuitry 10 encapsulated within an extruded polymer material 12 such as Esthane, a polyurethane thermoplastic elastomer, which acts as an electrical 30 insulator and which protects the LED circuitry from damage due to ingress of moisture. The insulating material 12 is at least partially transparent or translucent to permit light to pass through it.

35 As shown in Figure 2 the circuitry 12 comprises three substantially flat elongate conductors 14,16,18, typically made of copper. The three conductors

- 5 14,16,18 are spaced apart from one another and the adjacent conductor edges, and thus clearances 20,22 between them, are configured in a regular undulating pattern. The clearances 20,22 become filled with the 5 extruded insulating material 12 during manufacture.

The elongate conductors 14,16,18 can be formed from a single conductive strip using conventional circuit board manufacturing technology. For example, a copper coating may be provided on an insulating substrate 23 10 and the clearances formed by etching away portions of the copper. - -

A number of light producing devices, preferably LEDs, 24 are operatively connected to two of the three 15 elongate conductors 14,16,18, either elongate conductors 14 and 16 or conductors 16 and 18. Elongate conductors 14,16,18 are separately connected to a power source (not shown) . Power is selectively supplied to the elongate conductors 14,16,18 in order 20 to illuminate the LEDs 24 in predetermined sequences.

As seen in Figure 1, the LEDs connected between conductors 14 and 16 are located across troughs in the undulating clearance 20, while the LEDs connected 25 between conductors 16 and 18 are located at peaks of the undulating clearance 22. In addition, the spacing of adjacent LEDs is equal to 1 times the period of the undulation. In this way, all the LEDs 24 lie in a substantially straight line along the centre line of 30 the lighting strip, which is desirable in many applications. It will be appreciated that to achieve this effect minimum spacing between adjacent LEDs 24 is half a period and higher possible spacings must be odd multiples of half a period, i.e. 1, 3, 5 etc. 35 Nevertheless, other spacings could be used if an arrangement of LEDs along the centre line is not required.

6 - Due to the simplicity and continuity of the circuit layout, a particular advantage of the present invention is the ability to divide the strip at any point or points along its length without loss of 5 circuit integrity to any of the sections thus produced. Another advantage of the lighting strip as described by the present invention is that the number 10 of LEDs provided on the lighting strip can be increased or decreased as desired. In particular LEDs can be removed without the need to provide a replacement component to ensure continuity of the circuit in the locations where they are omitted, as 15 would be the case in the prior art.

A further advantage of the present invention is its potential to drive the LEDs in a variety of predetermined sequences. In the present invention the 20 lighting strip comprises two circuits, formed by separately combining each of the two outer elongate conductors 14,18 with the central elongate conductor 16. The operational sequences by which the LEDs are lit can be achieved by selectively supplying a power 25 to one or more of the three elongate conductors. The preferred embodiment of the present invention utilises LEDs as light producing devices because this increases the number of sequences in which the lighting strip can be operated. This is achieved by reversing the 30 polarity of the supply lines to provide a further two circuits. In a longitudinal direction along the lighting strip the LEDs may be arranged in similarly biassed pairs, the bias alternating with every LED pair, although it should be noted that alternative 35 configurations of the LEDs are contemplated.

Application of positive voltages or negative voltages to one or a combination of the elongate conductors

- 7 - will result in the LEDs being lit in sequence.

Another important feature of the lighting strip of the preferred embodiment of the present invention 5 is that it is directly driven by a controlled voltage source (not shown) thus removing the requirement for resistors within the lighting strip itself. Removal of the resistors from the lighting strip reduces the capacity for the lighting strip to heat up and 10 consequently reduces the power consumption of the lighting strip.

Providing a controlled voltage source directly to the LED lighting strip does demand a greater level of 15 control from the driving system but provision of this control provides the lighting strip with further advantages. Using a micro controller and a programmable power source to drive the lighting strip enables different technology and/or colour LEDs to be 20 mixed on a parallel track. Use of a drive system such as this allows a greater degree of monitoring of the performance of the lighting strip and hence provides for fault detection.

25 The lighting strip can be satisfactorily driven by applying a controlled voltage source to a single end of the lighting strip. However, the application of two controlled voltage sources, one at each end of the lighting strip provides supply continuity. This is of 30 particular importance for relatively long runs of the lighting strip and/or where monitoring is required.

Many of the aforementioned applications of lighting strips require large numbers of lights to be 35 run along extensive distances. As a result the conductor lengths are long and there is a significant voltage drop across them. If the voltage drop is large

- 8 enough the supply will fall below the threshold voltage of the LEDs and they will fail to light.

To partially compensate for the voltage drop 5 along the elongate conductors the present invention also provides a method of operating the lighting strip which involves driving the LEDs by a series of medium frequency pulses. If the LEDs are intermittently driven in this way they can be run at a higher lumen 10 output without detriment. Although the LED is not lit between pulses there is no noticeable reduction in lumen output as the high lumen output pulse is remembered by the human eye. In between pulses the LEDs can cool down and this keeps the operating energy 15 within the working limits of the LED.

For applications that demand that power consumption of the strip to be minimal, then normal lumen output from the LEDs can be achieved using the 20 above method but at a much improved efficiency.

Certain applications may also require minimization of Electro Magnetic Compatability (EMC) interference for use in particularly sensitive 25 environments. The present invention can significantly reduce such interference by providing a standing DC voltage just below the threshold level required to operate the LEDs and superimposing small pulses which raise the voltage above the threshold in order to 30 switch the LEDs on. The switching voltage is thus a fraction of the full operating voltage then and the electro magnetic interference can be significantly reduced. For optimum performance the voltage pulses can have soft edges.

As an alternative, the lighting strip is its ability could also be driven by a steady state

- 9 voltage. This allows for static operation, i.e ON/OFF.

Furthermore it is anticipated that the or each of the system drivers may be configured to provide 5 condition monitoring of the lighting strip. This will enable comparative analysis to be carried out in order to aid with the detection of faults within the components of the lighting strip.

10 It will be appreciated that the present invention provides an improved lighting strip with increased functionality and flexibility of operation. The skilled reader will realise that a number of modifications or variations to the precise details 15 described herein may be made without departing from the scope of the claims.

For example, the LED lighting strip of the present invention may be manufactured with a number of 20 different configurations of the LEDs 24. The present invention may have any number of rows of LEDs 24 by the addition of further elongate conductors to the lighting strip. The LEDs 24 may be located substantially away from the centreline of the lighting 25 strip or may have LEDs 24 configured in regular or irregular patterns along the lighting strip. If the LEDs 24 are to be situated substantially away from the centreline of the lighting strip the elongate conductors 14, 16,18 need not be undulating and may 30 instead be configured in different patterns or simply be generally straight and parallel, for example.

Claims

- 10 CLAIMS

1. A method of operating a lighting strip which comprises at least three elongate conductors spaced 5 apart from one another, and a plurality of light producing devices, each connected to two of the at least three conductors, the method comprising supplying a series of voltage pulses to the conductors in order to operate the light producing devices.

2. A method as claimed in claim 1, further comprising the step of maintaining a first voltage across the light producing devices below a threshold voltage required to operate the light producing devices, and 15 to supply pulses of a second voltage sufficient, in combination with the first voltage, to exceed the threshold and thereby operate the light producing devices. 20

3. A method as claimed in claim 1 or claim 2, further comprising the step of providing a system driver at each end of the strip connected to each of the elongate conductors and selectively controlling the system drivers so as to operate the light producing 25 devices in a variety of pre-determined sequences.

4. A method of operating a lighting strip substantially as hereinbefore described with reference to the accompanying drawings.

: 391391: JDCG: JDCG: LONDOCS