LED TUBE AND LED BULB

Technical Field

[1] The present invention relates to light emitting diode (LED) lighting , more particularly, LED tube suitable for replacing fluorescent tube, and more specifically LED tube that could light up areas of interest with minimal light wastage. Background Art

[2] Fluorescent tubes are used for general lighting in many places. This is due to the fact that fluorescent tubes are more efficient than traditional incandescent light bulbs.

[3] The sizes of fluorescent tubes have been standardized. Common diameters of fluorescent tubes are 5/8 inches, 8/8 inches and 12/8 inches and are called T5, T8 and T12 respectively. The common lengths of T8 tubes are 2 ft and 4 ft long. Other sizes of fluorescent tubes exist.

[4] There is a push towards replacing fluorescent lighting with LED lighting as the latter is potentially more energy efficient and lasts longer. The most direct method is to replace existing fluorescent tubes with LED tubes.

[5] One such invention is disclosed in US Patent No. 6,860,628. The invention provides a 'drop-in' replacement for fluorescent tubes. Referring to FIG. 1, the LED lamp 101 comprises an elongated hollow tube 102 with end caps 103 and connectors 104 similar in size to conventional fluorescent tubes, containing a plurality of LEDs 105 and appropriate electrical components (not shown). The LEDs 105 are connected in series and point in the same direction vertically downwards. Disclosure of Invention Technical Problem

[6] A fluorescent tube produces diffused lighting and emits light in all directions. In a typical fluorescent tube ceiling lamp, the floor directly under it is the brightest. The lighting level on the floor decreases gradually as the horizontal displacement from the fluorescent lamp increases (because of inverse square law).

[7] Existing LED tubes have a different light emittance behavior. A LED tube is made up of many LEDs. Each LED produces a little light and together it produces the amount of light required. However, each LED is directional. This results in the light from current LED tubes to be directional as well. Each LED also has a viewing angle. This means that areas outside the viewing angle of the LEDs are relatively dark. In other words, the floor area directly under the LED tube is bright. However, the floor area relatively further away is relatively dark.

[8] Referring to FIG. 2, the graph 60 (not to scale and for illustration purpose only) compares the illuminance level on the floor illuminated by a fluorescent tube ceiling lamp and a typical LED tube ceiling lamp. Current or typical LED tube uses LEDs with the same large viewing angle (more than 90 degrees) and point all the LEDs in the same direction. The graph 60 has the vertical axis 61 representing the illuminance level on the floor level measured in lux. The graph 60 has the horizontal axis 62 representing the horizontal displacement measured in meters from the centre of the light tube. The minimum illuminance level required is represented by the line 63. The illuminance level of the fluorescent tube and LED tube are represented by the curves 64 and 65 respectively. Curve 64 is more spread out as the fluorescent light is diffused whereas curve 65 is more focused as the LED light is directional. For a fluorescent tube ceiling lamp, any areas between displacements 66 and 67 are sufficiently bright. For a LED tube ceiling lamp, any areas between displacements 68 and 69 are sufficiently bright.

[9] The implication in the different characteristics between the fluorescent tube and the current LED tube is that we cannot simply substitute any existing fluorescent lamps using fluorescent tubes with current LED tubes without further analysis. Many a times, existing fluorescent lamps are spaced far apart to reduce the number of such lamps and to minimize wastage. For such fluorescent lamps, replacing the fluorescent tubes with LED tubes will result in areas between the lamps to be too dark. As for new installations, the distance between two LED tube lamps will need to be much closer than for two fluorescent tube lamps. This might not be acceptable to clients or it might result in less efficient use of resources as each LED tube comprises many other components other than LEDs.

[10] Another problem is that there is often a mismatch between the area to be lighted up and the actual area lighted up by fluorescent tube or current LED tube. As light from a light tube spreads out, the area lighted up tend to be similar to a circle or an oval shape. Based on the minimum lighting level required, the diameter of the circle lighted up might be 8 meters. However, the area to be lighted up might be a rectangle, such as a covered walkway, corridor or staircase. The width of a covered walkway could typically be 1.5 meters. Although fluorescent lamps can be placed 8 meters apart, much of the light from a fluorescent tube falls outside the area to be lighted up and is wasted. This is true also for existing LED tubes, even when the lamps are placed nearer, such as 5 meters apart. Technical Solution

[11] In a LED tube, there are many LEDs. By using LEDs with different viewing angles and pointing them in the appropriate directions, we can overcome the above problems.

[12] LEDs with larger viewing angles have smaller luminous intensity and the light they emit is less focused and are good for illuminating nearer areas. LEDs with smaller viewing angles have larger luminous intensity and the light they emit are more focused and are good for illuminating areas further away. Hence in the LED tube, LEDs with larger viewing angles point to and illuminate nearer areas while LEDs with smaller viewing angles point to and illuminate areas further away. Furthermore, the LEDs are positioned such that the light from the LEDs with different viewing angles overlap each other and illuminates the whole area intended from near to far.

[13] LED tubes making use of the above solution can outperform existing fluorescent tubes, providing more light to the areas required and yet using less power.

[14] In order to place all the LEDs into the limited space of a tube, the LEDs need to be spaced out longitudinally. In order for the LEDs to point in the correct directions, LED housings can be molded with the appropriate angles and the LEDs fixed onto them. Advantageous Effects

[15] This invention overcomes the disadvantages and limitations of prior art. This invention outperforms existing fluorescent tubes and can be used to replace them in existing installations. This invention makes better use of the lighted emitted from the LEDs than current LED tubes, thereby saving energy. For new installations, this invention can be placed further apart as compared to existing LED tubes and this means better use of resources. Description of Drawings

[16] The accompanying drawings are solely for purposes of illustrating the concepts of the invention and are not drawn to scale. The embodiments shown in the accompany drawings, and described in the accompanying detailed description, are used as illustrative embodiments and should not be construed as the only manner of practicing the invention. Also, the same reference numerals, possibly supplemented with reference characters where appropriate, have been used to identify similar parts. These and other objects and features of this invention will be clear and apparent to those skilled in the art upon reading the detailed description together with the drawings, wherein:

[17] FIG. 1 shows a prior art of a LED tube;

[18] FIG. 2 shows a graph comparing the illuminance levels on the floor by lamps using a fluorescent tube and a current LED tube;

[19] FIG. 3 shows an angled view of a LED tube;

[20] FIGS. 4a to 4e show cross-sections of the LED tube;

[21] FIG. 5 shows a graph comparing the illuminance levels on the floor by lamps using a fluorescent tube, a current LED tube and the invented LED tubes;

[22] FIG. 6 shows part of a circular LED tube with LEDs with various tilt angles;

[23] FIG. 7 shows a cross-section of the LED tube without the bottom half;

[24] FIG. 8 shows a LED bulb with LEDs with various tilt angles. Best Mode

[25] Referring to FIG. 3, it shows an angled view of a LED tube 1. It comprises a hollow tube 2, end caps 3a and 3b, and LEDs 6 (6a to 6e). The LEDs 6a to 6e are held in place by LED housings 8a to 8e respectively, so as to point in the appropriate directions. The LED housings are preferably made of plastic. The top part 2a of the hollow tube 2 is opaque, so that any wiring or electrical components (not shown) can be hidden there. The bottom part 2b of the hollow tube 2 is transparent or translucent, so that light from the LEDs 6 can pass through. The hollow tube 2 is preferable made of plastic as it does not break and can be produced relatively easily even for two colors (opaque for top part 2a and transparent for bottom part 2b) using plastic extrusion method, although glass or other suitable materials can also be used. The end cap 3a has electrical connector pins 4a and 4b while end cap 3b has electrical connector pins 4c and 4d. The end caps 3 together with electrical connector pins 4 are similar with the end caps of fluorescent tubes, and can fit into the sockets designed for fluorescent tubes. Electrical components such as transformer, rectifier, capacitor, resistor or surge protector (not shown) can also be hidden at the ends of the tube, which can be made opaque with stickers 5a and 5b. The stickers 5a and 5b can also contain instructions or information about the LED tube 1. Of course, the stickers are not a critical component of the invention. The electrical components can also be hidden within the end caps 3a or 3b if they are made longer.

[26] The LED tube 1 can be designed to accept alternating current power supply directly.

In such a case, the electrical assembly comprising electrical components (not shown) like the step-down transformer to reduce the voltage to the required level, a rectifier to convert the alternating current power supply into a direct current supply, a capacitor to smooth out the voltage, a surge absorber to absorb any surge in voltage or current can be included in the LED tube. Alternative electrical designs are possible and are well documented and are obvious to those skilled in the art. The electrical components can also be externalized, that is to say they are outside the LED tube. In such a case, the LED tube accepts the appropriate direct current voltage. A LED driver, which is commonly available in the market and converts alternating current voltage and outputs constant direct current voltage, can also be used to provide the required direct current voltage to the LEDs. In such a case, the internal electrical design will be much simpler, without the need for rectifier or capacitor. In terms of the circuit design for the LEDs, one common way is to divide the LEDs into groups. The LEDs in the same group are connected in series but every group is connected in parallel to the direct current source. Other circuit designs are available, depending on the need, and are well known in the art.

[27] The LEDs 6a has the largest viewing angle and point directly downwards while the LEDs 6e has the smallest viewing angle and point furthest away. This will become clearer with the next few drawings.

[28] Referring to FIG. 4a, it shows the cross-section 1-1 in FIG. 3. The LEDs 6a are mounted on printed circuit boards (PCBs) 7a. The PCB 7a together with the LEDs 6a fit securely into the LED housing 8a. The LED housing 8a fits nicely in the hollow tube 2 supported by nibs 2c at the junction of the top part 2a and bottom part 2b of the hollow tube 2. The bottom part 2b has a smooth surface, although a profiled surface can also be used. An appropriate profiled surface for bottom part 2b can help to diffuse or disperse the light from the LEDs. The LEDs 6a have a viewing angle of 60 degrees. The direction of the LEDs 6a is fixed according to the shape of the LED housing 8a.

[29] For clearer understanding, we define tilt angle as the angle measured in an anticlockwise direction from the downward vertical to the direction of the LED.

[30] The tilt angle 9a (not shown) for LEDs 6a is 0 degrees (vertically downwards).

[31] Referring to FIG. 4b, it shows the cross-section 2-2 in FIG 3. The LEDs 6b (6bl and

6b2) are mounted onto PCBs 7b (7bl and 7b2) and fit into LED housing 8b. The LEDs 6b have viewing angle of 40 degrees. The tilt angles 9bl and 9b2 for LEDs 6bl and 6b2 are -20 degrees and 20 degrees respectively. Referring to FIGs. 4c, 4d and 4e, the LEDs 6c, 6d and 6e are mounted onto PCBs 7c, 7d and 7e respectively and fit into LED housings 8c, 8d and 8e respectively. The LEDs 6c, 6d and 6e have viewing angles of 30 degrees, 15 degrees and 10 degrees respectively. The tilt angles 9cl, 9dl and 9el for LEDs 6cl, 6dl and 6el are -40 degrees, -60 degrees, and -70 degrees respectively. The tilt angles 9c2, 9d2 and 9e2 for LEDs 6c2, 6d2 and 6e2 are 40 degrees, 60 degrees, and 70 degrees respectively.

[32] The viewing angles of the LEDs are chosen so that light wastage is minimized. Floor to ceiling height can typically range from 2 meters to 4 meters. Taking a height of 2.5 meters commonly found in some residential buildings, the LED 6a with a viewing angle of 60 degrees will project a light cone of 2.8 meters on the floor. This is suitable for illuminating corridors or walkways, which have widths of about 2 meters. The tilt angles are chosen so the light cones from one group of LEDs with the same viewing angles overlap the light cones from the next group of LEDs. So the light cones from LEDs 6a overlaps with the light cones from LEDs 6b; and the light cones from LED 6b overlaps the light cones from LED 6c and so on. As a result, the light cones from LEDs 6a, 6b, 6c, 6d and 6e creates a smooth continuous lighting for the intended area, just like the continuous lighting from a fluorescent tube.

[33] The viewing angles and tilt angles are described here to help explain the concept of the invention and are not meant to be the only solution or restricting the invention in any manner. Although the LEDs with larger viewing angles have smaller tilt angles, and LEDs with smaller viewing angles have larger tilt angles, the reverse is also possible. It is also possible to have one and the same viewing angle for all the LEDs, although the resulting LED might not be as efficient. Also, although only two LEDs per cross-section are described here, other numbers such as one or three LEDs per cross-section are also possible. The LEDs can also be staggered in its positioning in the lateral or longitudinal direction, such that the left and right LEDs are half spacing apart instead of being in line. Also, although in FIG 3, it shows 3 LEDs grouped together for each LED housing and tilt angle, it is done for simplicity and clarity and is not meant as a restriction. More likely, there will be more LEDs for larger tilt angles than smaller tilt angles.

[34] The LED tube uses less power and provides more light to the area required. Referring to FIG. 5, the graph 60 (not to scale and for illustration purpose only) now includes the illuminance level of the invented LED tube represented by curve 70. Curve 70 provides more light (higher illuminance level) and is more spread out as compared to curve 64 (fluorescent light) and is much better than the current LED tube as represented by curve 65. The area illuminated by the invented LED tube between displacements 71 and 72 meets the minimum lighting level as indicated by the line 63.

[35] The advantage of this new LED tube is that it can replace existing fluorescent tubes, without concern that certain areas between two existing lamps will be darker than before. For new lighting installations, the LED tubes can be placed further apart than existing LED tubes. In both cases, it translates into energy and material savings.

[36] Another aspect which lighting designers sometimes need to meet is uniformity level, which is the minimum lighting level divided by the maximum lighting level. Curve 73 represents the illuminance level of another LED tube, but with a different number of LEDs, viewing angles and tilt angles. Tilt angles with small discrete angle increments will make the lighting levels smoother, although more difficult to manufacture. For example, instead of having LEDs with tilt angles of 60 and 70 degrees, we can have LEDs with tilt angles of 60, 62, 64 66 68 and 70 degrees. Curve 73 provides much better uniformity levels than the other light tubes within the areas required. Many other illuminance curves are possible by changing the number of LEDs, type of LEDs, their viewing angles and tilt angles. Mode for Invention

[37] Other modes of invention exist. Depending on the need, various configurations using the concept above can be used.

[38] If the LED tube above is mounted 2.5 meters above the floor, it provides good illumination for a rectangular area 2 meters wide and 9 meters long. This is useful for walkways or corridors. For wider areas, such as 5 meters wide, LEDs with larger viewing angles can be used. Alternatively, some LEDs can tilt in the same planes as the length of the tube. The other LEDs can tilt in the planes perpendicular to the length of the tube, or tilt in a combination of both planes.

[39] If the LED tubes are to be placed nearer, such 6 meters apart, then the design can be simplified. Instead of installing the LEDs with 9 tilt angles (-70, -60, -40, -20, 0, 20, 40, 60 and 70 degrees), only two tilt angles, such as -20 degrees and +20 degrees, are sufficient. Again depending on the need, if the area to be lighted is not symmetrical about the centre of the LED tube, non- symmetrical tilt angles can be used. For example, the LED tube can have LEDs with tilt angles such as -10, 0, 30 and 50 degrees so as to achieve non-symmetrical lighting.

[40] Other than traditional through-hole LEDs, which have two legs, other new LEDs have been developed. There are Piranha LEDs, which have four legs (two positive and two negative), and surface mount LEDs, which have six legs (three positive and three negative) or more. The new LEDs are much brighter than traditional LEDs and can be used in place of the traditional LEDs if desired. Some new LEDs produce diffused lighting. Such LEDs can also be used and installed with various tilt angles. If the area to be lighted is far and small, LEDs lens can be used in conjunction with such LEDs to focus the light. White LEDs, single color LEDs, or full color LEDs can also be used with this invention.

[41] So far, the LEDs tubes described are hollow and longitudinal. Solid tubes whereby the LEDs are cast in are also possible. Circular tubes can also be used. Referring to FIG. 6, it shows part of a circular LED tube 20. The LEDs 21 and 22 within are tilted so as to achieve the required illumination. The number of LEDs, their viewing angles, tilt angles, electrical design, method of securing and so on can be similar and to the longitudinal tubes and will be obvious to those skilled in the art.

[42] Thus far, the design has been geared towards using existing fluorescent tube sockets.

However, for new installations, this is no longer a constraint. The end caps can be of a different design. Instead of two end caps, one end cap would be sufficient. In such a case, both the positive and negative electrical connectors will be at only one end, which is the end with the end cap. Further, the design can deviate from a full hollow tube. FIG. 7 shows the cross-section of an alternative design LED tube. The cross- section is similar to that in FIG. 4c, comprising the top part 2a, the LEDs 6c mounted onto PCB 7c and fit into LED housing 8c, except it does not comprise the bottom part 2b. The bottom part does absorb some light as the light emitted from the LEDs pass through it. Hence without it, the LED tube will be even brighter.

[43] The concept of this invention can also be extended to LED bulbs. Referring to FIG. 8

, it shows the LED bulb 30 with a threaded end cap 31, which provides the positive and negative electrical connections and fits into an electrical bulb socket, an opaque body 32 to conceal the electrical components (not shown), and a transparent or translucent head 33 for light to pass through. It further comprises a LED housing 34, which fixes the tilt angles of the LEDs 35, 36 and 37. The LED bulb 30 being not longitudinal allows the LEDs 35, 36 and 37 to be placed in a generally forward all round direction. Of course, as before, the number of LEDs, their viewing angles and tilt angles can be determined based on needs. Many other types of sockets or configurations are available and will be obvious to those skilled in the art. The light generated is more spread out than conventional LED bulbs, which use LEDs with only one viewing angle and the LEDs all point in the same direction. The invented LED bulb can be designed to replace incandescent light bulbs, compact fluorescent light bulbs or existing LED bulbs.

[44] While the present invention has been explained by reference to the preferred embodiments described above, it will be appreciated that the embodiments are only illustrated as examples to assist understanding of the present invention and are not meant to be restrictive on its scope. In particular, the scope, ambit and spirit of this invention are meant to include the general principles of the invention as inferred or exemplified by the embodiments described above. More particularly, variations or modifications which are obvious or trivial to persons skilled in the art, as well as improvements made on the basis of the present invention, should be considered as falling within the scope and boundary of the present invention.

[45] Furthermore, while the present invention has been explained by reference to LED tube and LED bulb, it should be appreciated that the invention can apply, whether with or without modifications, to other types LED lighting without loss of generality. Industrial Applicability

[46] This invention allows for the replacement of existing fluorescent tubes with LED tubes. This will reduce energy usage. This invention can also be used in new installations, and be placed further apart than existing LED tubes, thereby saving resources.