EP2649364B1

EP2649364B1 - Bulb - shaped led light source

Info

Publication number: EP2649364B1
Application number: EP11790589.3A
Authority: EP
Inventors: Takahiro Konomoto; Takashi Noguchi; Takashi Osawa
Original assignee: Osram GmbH
Current assignee: Osram GmbH
Priority date: 2010-12-10
Filing date: 2011-11-23
Publication date: 2015-07-15
Anticipated expiration: 2031-11-23
Also published as: WO2012076339A1; EP2649364A1; JP5628017B2; CN103261778A; JP2012124124A; CN103261778B

Description

[Technical field]

The present invention relates to bulb-shaped LED light sources.

[Background art]

In bulb-shaped light sources an outer tube globe lowers the intrinsic transmittance and from the point of view of luminous efficacy is thus counterproductive, but LEDs (light emitting diodes) have a high luminance and are thus dazzling when used for general lighting, and to suppress this it is known to arrange in front of an LED light source an opal outer tube globe having a light diffusing effect.
For example, Figure 7 is a cross sectional view showing a conventional LED bulb 200. The objective of the LED bulb 200 is to provide an LED bulb with which white light can be obtained with uniform luminance over a wide area of illumination using a simple configuration, and with which the light distribution pattern can be altered simply, which can be connected directly to an ordinary commercial power supply and which is compatible with commonly used incandescent light bulbs.
The LED bulb 200 comprises a cover 202 which is provided at one end with a metal cap 201 and which widens in a trumpet shape toward an opening at the other end, an outer tube globe 205 having a light diffusing layer 206 on its inner surface and fitted to the opening of the cover 202, a substrate 203 provided inside a substantially spherical body 207 formed from the cover 202 and the outer tube globe 205, and LED elements 204 mounted onto the outer surface of the substrate 203 facing the outer tube globe 205. Further, the outer tube globe 205 may also comprise a uniform material (such as acrylic) having a light diffusing effect.
Further, the substrate 203 is plate-shaped and parallel to the outer surface of the opening of the cover 202. In other words, a plurality of LED elements 204 are arranged on the planar substrate 203 (see for example Patent literature article 1).

[Prior art literature]

[Patent literature]

[Patent literature article 1] Japanese Patent Kokai 2001-243807 . US2010/0277067 discloses a bulb-shaped LED light source of the prior art.

[Summary of the invention]

[Problem to be resolved by the invention]

With such an LED bulb 200, light emitted from the LED elements 204 illuminates the outer tube globe 205, and in some areas light from a plurality of LED elements 204 overlaps, while other parts are outside the illuminated area. In other words, there is a problem of non-uniform brightness.
Further, because the LED elements 204 are arranged on the same substrate 203 facing in the same illumination direction, the light distribution characteristics are completely different from an electric bulb or bulb-shaped fluorescent lamp even though the shape of the commercial product looks the same as an electric bulb, as the emitted light is concentrated in only one direction, as with a spotlight, perpendicular to the surface of the substrate 203. Conventionally, if used as a replacement light source in a lighting fixture in which the light source was an incandescent light bulb, there is a drawback in that the illumination intensity distribution of the whole room changes significantly, and typically ceilings and walls become extremely dark compared with the situation prior to replacement.
Further, when used as a light source for a downlight, distribution of light to the walls is not considered particularly important, so there is a tendency for the light distribution to be concentrated along the axis such that the directly-downward illumination intensity is the same as that of an incandescent light bulb. In this case, the component of the distributed light that is perpendicular to the central axis, being readily diffused and prone to loss at the outer tube globe 205, is reduced in relative terms, so the luminous efficacy is increased, but only the center of the light emitting surface has a high luminance, the luminance uniformity ratio on the surface of the outer tube is reduced, and there is thus a drawback in that non-uniformity occurs, in addition to which the problem that walls are dark also becomes more marked.
Further, having an extremely large value of n (the number of LED elements 204, where n is a natural number) would appear to solve the abovementioned problems. However in practice it is not possible to arrange a large number of LED elements 204 on the surface of the substrate 203, which has a limited surface area, in addition to which saleability would be reduced in terms of cost, and further the temperature would become too high, reducing the operating life of the LED elements 204 and greatly sacrificing a feature of the LED namely its long operating life characteristic.
Increasing the diffusion of the outer tube globe 205 and reducing its transmittance would improve the luminance uniformity ratio, but this would result in a reduction of the luminous efficacy of the lamp itself.
A factor that influences the luminous efficacy is that with a diffusion filter (outer tube globe 205) perpendicular to the optical axis of the illuminating light almost all of the light enters and passes through the filter medium while being attenuated. This is called the in-line transmittance. However, if light enters the filter obliquely, with an angle between its optical axis and the filter, then a portion of the light is reflected without entering the filter medium. In the case of the LED bulb 200, light reflected within the outer tube globe 205 is further reflected multiple times, and is separated into light that is illuminated out of the outer tube globe 205 and light that is lost within the outer tube globe 205. In other words, with an outer tube globe 205 having portions that are not perpendicular to the optical axis, the internal loss increases as the portion with a low incident angle increases, and the overall luminous efficacy decreases. Therefore, if a plurality of LEDs with a narrow light distribution angle are arranged in a planar fashion and a planar diffusion panel is installed perpendicular to all of the LED optical axes then the abovementioned loss will be reduced, but its performance as an alternative to an incandescent light bulb will be impaired.
If use of LED bulbs 200 becomes more widespread in the future and products are developed with a wide range of light distribution patterns then users will be able to select a product according to the application. However, currently due to the constraints of cost, selling price and sales volume, realistically products are not available with a wide range of light distribution patterns, and the main design strategy is for the directly-downward illumination intensity to be equivalent to that of existing incandescent light bulbs. We investigated balancing the elements "directly-downward illumination intensity", "distribution to walls" and "luminance uniformity ratio of the light source itself (degree of absence of non-uniform luminance)" to be optimal for practical use. Thus the aim is to widen the range of application by optimizing the method of distribution of the current total amount of light, without increasing the intrinsic efficiency of the LED elements 204, and without adding light distributed to the walls while maintaining the directly-downward illumination intensity.
The present invention aims to overcome problems such as those mentioned above by providing a bulb-shaped LED light source with which the luminance uniformity ratio on an outer tube globe similar to an incandescent light bulb is improved, in other words with which the occurrence of light non-uniformities can be reduced, without reducing efficiency.
Further, while it would be possible to conceive of a design means whereby a plurality of LED elements are used and the light distribution angle of each is varied as appropriate, employing this method would result in an industrially complex process, and even if the total number of LED elements used were the same there would be a plurality of different types, and thus the ability to mass produce would be reduced, cost would increase, and lead times for preparing materials would increase, and it was thus a premise that this method would not be employed.
Further, a method has also be conceived whereby the optical axis of each LED is varied without changing the light distribution angle, and this has been commercialized by our company as Parathom Classic A, but this method also has a problem from an industrial point of view in that the LEDs cannot be installed directly on the surface of a single substrate, and it was thus not included in our investigation.
Therefore, in resolving the current problem, the design method to be employed was limited to a design in which all of the LED elements have the same light distribution angle, eliminating the need for complex identification or distinct usage of LED elements, and in which the LED elements are installed with the same illumination direction on a substrate, and in which all of the optical axes are in a direction perpendicular to the surface of the substrate.
Here, the design should preferably be such that there is uniform distribution of light in the lower hemisphere, and also a similar distribution of light in the upper hemisphere, but realistically LED elements do not yet exist that would be able to satisfy such demands, and our aim was thus a design whereby light distribution in the lower hemisphere is as uniform as possible, and whereby directly-downward illumination intensity is distributed to some extent.
Further, the in-line transmittance of the outer tube globe was set to be approximately 90%. However, this transmittance is a phenomenon that is essentially independent of the present invention, and the advantages of the present invention are not limited to 90%.
As shown in Figure 8, if the light intensity on the central axis of an LED element is defined as 100%, then the light distribution angle is the two-dimensional angle from the central axis to the angle at which the light intensity has reduced to 50% of the value on the central axis, where said angle is the angle from the central axis as viewed from the luminescent center of the LED. In other words it is the angle on both sides of the central axis at which the light intensity has reduced to 50%. Therefore, although in practice a small amount of light illuminates outside of this area, the light distribution area is defined here as the area inside the light distribution angle of the LED, in order for design verification to be unambiguous.

[Means of overcoming the problem]

The bulb-shaped LED light source according to the present invention is a bulb-shaped LED light source being a light source of a type that has a built-in lighting circuit and can be lit using a commercial power supply, emitting light over a range of approximately 2nSt (steradian), using LED (light emitting diode) elements as a light source, having an electric bulb-shaped appearance, and not having a wide light distribution like that of an electric bulb, and being an alternative light source to an incandescent light bulb having an E or B metal cap, and further having an outer tube globe in front of the LED light source in imitation of an incandescent light bulb, characterized in that:

at least n (a natural number of 4 or more) LED elements are arranged within the outer tube globe on the same surface of a substantially planar substrate;
each LED element has a light distribution angle of at least 60° and 120° or less, and the central axis of the light distribution angle is perpendicular to the surface of the substantially planar substrate;
the light distribution areas inside the light distribution angle within which each LED element illuminates light onto the inner surface of the outer tube globe are made to overlap;
and a part, including on the inner surface of the outer tube bulb on the central axis of the lamp, of the overlap comprises n overlapping light distribution areas, and the n overlapping light distribution areas comprise at least 10% and no more than 80% of the inner surface of the outer tube globe.

The bulb-shaped LED light source according to the present invention is characterized in that the area not included in the light distribution area of any of the LED elements is less than 30% of the inner surface of the outer tube globe.

[Advantages of the invention]

With the bulb-shaped LED light source according to the present invention, by employing the abovementioned configuration it is possible to improve the luminance uniformity ratio on the outer tube globe without reducing the efficiency, in other words to reduce the occurrence of light non-uniformities.

[Brief explanation of the figures]

[Figure 1] is a diagram showing mode of embodiment 1, being a side elevation (a) and a front elevation (b) of a bulb-shaped LED light source 100.
[Figure 2] is a diagram showing mode of embodiment 1, being a diagram showing the light distribution characteristics of a bulb-shaped LED light source.
[Figure 3] is a diagram showing mode of embodiment 1, being a schematic drawing showing the light distribution area on the outer tube globe when the number of LED elements n = 3.
[Figure 4] is a diagram showing mode of embodiment 1, being a schematic drawing showing the light distribution area on the outer tube globe when the number of LED elements n = 4.
[Figure 5] is a diagram showing mode of embodiment 1, being a schematic drawing showing the light distribution area on the outer tube globe when the number of LED elements n = 5.
[Figure 6] is a diagram showing the design parameters and evaluation results for comparative examples 1 to 7 and embodiments 1 to 4.
[Figure 7] is a cross sectional view of a conventional LED bulb 200.
[Figure 8] is a diagram defining the light distribution angle of an LED element.

[Mode of embodying the invention]

Mode of embodiment 1.

Figure 1 to Figure 6 are diagrams showing mode of embodiment 1, where Figure 1 is a side elevation (a) and a front elevation (b) of a bulb-shaped LED light source 100; Figure 2 is a diagram showing the light distribution characteristics of a bulb-shaped LED light source; Figure 3 is a schematic drawing showing the light distribution area on the outer tube globe when the number of LED elements n = 3; Figure 4 is a schematic drawing showing the light distribution area on the outer tube globe when the number of LED elements n = 4; Figure 5 is a schematic drawing showing the light distribution area on the outer tube globe when the number of LED elements n = 5; and Figure 6 is a diagram showing the design parameters and evaluation results for comparative examples 1 to 7 and embodiments 1 to 4.
As shown in Figure 1, the bulb-shaped LED light source 100 is provided with a metallic heat dissipation component 2 which is provided at one end with a metal cap 1 and which widens in a trumpet shape toward an opening at the other end. It comprises the heat dissipation component 2, an outer tube globe 5 having a light diffusing layer 6 on its inner surface and fitted to the opening of the cover 2, a substrate 3 provided inside a substantially spherical body 7 formed from the heat dissipation component 2 and the outer tube globe 5, and LED elements 4 mounted onto the outer surface of the substrate 3 facing the outer tube globe 5.
The bulb-shaped LED light source 100 in the present mode of embodiment has the following characteristics.

(1) The light source is LED elements 4 (light emitting diodes).
(2) It has a bulb-shaped appearance (see Figure 1).
(3) It does not have a wide light distribution like that of an electric bulb, and is a light source with a built-in lighting circuit which can be lit using a commercial power supply, emitting light over a range of approximately 2n StRad (steradian).
(4) It is an alternative light source to an incandescent light bulb having an E metal cap such as an E26 metal cap or an E17 metal cap, or a B metal cap, as prescribed in JIS C7709-1, and is further a bulb-shaped LED light source 100 having an outer tube globe 5 in front of the LED light source in imitation of an incandescent light bulb.
(5) At least n (a natural number of four or more) LED elements 4 are arranged in a planar fashion on a substrate 3 within the outer tube globe 5.
(6) Each LED element 4 has a light distribution characteristic (light distribution angle) of at least 60° and 120° or less (see Figure 2 and Figure 8 for details of the light distribution angle). It should be noted that with an LED element 4 of 120° or more, the light distribution angle is wide and the illuminating angle is too wide for a light source employing an outer tube globe 5, since although there is no serious problem relating to non-uniform brightness, on the other hand the losses at the outer tube globe 5 are large, the efficiency as a light source is low, and it is difficult to increase the directly-downward illumination intensity.
(7) The light distribution areas of each of the LED elements 4, where the light is distributed over the inner surface of the outer tube globe 5, are arranged so as to overlap.
(8) The overlap includes a portion in which n light distribution areas overlap, and the portion in which n light distribution areas overlap constitutes at least 10% of the inner surface of the outer tube globe 5.
(9) The area not included in the light distribution area of any of the LED elements 4 (referred to as zero overlap hereinbelow) is less than 30% of the inner surface of the outer tube globe 5.

A survey of the causes of non-uniform brightness on the outer tube globe 205 of a conventional LED bulb 200, revealed that non-uniform brightness was generated for the following two reasons.

(1) Light emitted by a specific LED element 204 is illuminated at a specific angle, but the distance from each LED element 204 to the inner surface of the outer tube globe 205 within the area of illumination is different.
(2) There are areas in which the light illuminated from a plurality of LED elements 204 overlaps and areas in which it does not overlap.

It was found from the results of a series of surveys by the inventors that the effect of the former (1) was smaller that that of the latter (2) with regard to light non-uniformities.
It was further found from the series of surveys that if the light distribution overlaps symmetrically around a point then non-uniformities are relatively unobtrusive.
In order to improve the luminance uniformity ratio on the outer tube globe 5, the inventors investigated the latter (2). The results are shown in Figure 6. It should be noted that comparative example 1 (1) to comparative example 6 (6) and embodiments (7) to (9) in Figure 6 correspond to (1) to (9) in Figure 3 and Figure 4, and embodiment (11) corresponds to (11) in Figure 5. For comparative example 7 (10) in Figure 6, the corresponding schematic drawing showing the light distribution area on the outer tube globe 5 has been omitted. In the schematic drawing showing the light distribution area for comparative example 6 (6) in Figure 4 (6), the LED elements 4 arranged in positions on a concentric circle have been moved toward the center.
Light emitted from n LED elements 4 generates a maximum overlap of n overlapping light distribution areas. Depending on the arrangement of the LED elements 4 and the selected light distribution angle, the maximum number of overlaps may be less than n. Here, the distances between the LED elements 4 and the inner surface of the outer tube globe 5 only fall within an extremely limited range, and this cannot be a factor that causes a significant difference, so the luminance tends to depend on the number of overlapping light distribution areas rather than on differences in the distance from the LED elements 4 to the illuminated inner surface of the outer tube globe 5.
Further, cases in which the luminance gradually decreases from the center of the outer tube globe 5 toward its periphery tend not to be perceived as non-uniform luminance, in other words no discomfort was felt with regard to graduations in luminance. In the survey the luminance uniformity ratio was evaluated not by taking multiple measurements of luminance on the outer tube globe 5 of a single light source and assessing variations thereof quantitatively, but by means of a sensory evaluation relating to perceived non-uniform brightness when an actual light source is viewed, where the testers assigned X if discomfort was felt, Δ if some discomfort was felt, and O if there was no problem. The design standard was set as regions assigned 'O', being of a level satisfying the market.
Therefore in order to increase the luminance uniformity ratio, it is important to select LED elements 4 having a large light distribution angle, to use a large number n of LED elements 4 and to arrange them on the substrate 3 at the center of and/or on a circle concentric with the center of the substrate 3, and to make the zero overlap area narrow. On the other hand, in order to increase the directly-downward illumination intensity it is important for the light distribution layer with n overlaps to be provided on the axial line of the lamp (bulb-shaped LED light source 100). In order to increase the luminous efficiency of the whole lamp it is important to employ LED elements 4 having a light distribution angle that is as narrow as possible.
In order to achieve customer satisfaction by balancing these contradictory propositions, it is preferable for the number n (n is a natural number) of LED elements 4 to be at least four or more. As shown in Figure 3, if the number n of LED elements 4 is three, then LED elements 4 with an extremely wide light distribution angle are required, and thus losses within the outer tube globe 5 increase, and the luminous efficacy of the overall lamp (bulb-shaped LED light source 100) is unsatisfactory.
It was further found that, if the number n of LED elements 4 is three, then incorporating the luminance uniformity ratio and point symmetry into the design results in an arrangement such as that in Figure 3, in which the overlap in the central portion is a problem, and it is not possible to achieve a high directly-downward illumination intensity. Therefore n is preferably four or more. In the comparative example which uses 90° with n=3, a light distribution area is generated at the center having an overlap of n=3, but it was not possible to obtain both satisfactory luminance uniformity ratio and directly-downward illumination intensity at the same time.
If the illuminating angle is wide then it is easier to produce an n-overlap light distribution area, but on the other hand illumination losses inside the outer tube globe 5 increase, so a light distribution angle (θ₁ in Figure 2) of 120° or less is preferable. Also, if the illuminating angle is too narrow then it is difficult to generate an n-overlap area, and so the light distribution angle is preferably at least 60°.
Increasing the directly-downward illumination intensity is also an important design factor, and there should at least be an n-overlap light distribution area on the outer tube globe 5 on the center line of the lamp (bulb-shaped LED light source 100).
Further, a substantially satisfactory directly-downward illumination intensity cannot be obtained unless the n-overlap light distribution area on the outer tube globe 5 occupies at least 10% of the whole. Meanwhile, if the LED elements 4 are arranged in positions on a concentric circle then non-uniform brightness becomes less noticeable on visual observation.
For all the LED elements 4, use was made of typical white LED elements comprising blue LEDs combined with yellow phosphor, with each element having an output of 100lm and a rated power consumption of 1W. Then, five types were prepared, the only difference between them being the light distribution angle, using light distribution angles of 30°, 60°, 90°, 120° and 150°, and one element was arranged at the center of the 55mm diameter printed substrate 3 shown in Figure 1, and in some cases a plurality of LED elements 4 were arranged on a concentric circle from the center of the substrate 3 in symmetrical positions around said element, and bulb-shaped LED lamps (bulb-shaped LED light sources 100) of a type with an E26 metal cap were manufactured by way of experiment, and a comparative evaluation was performed.
No particular explanation is provided, but since the temperature of the substrate 3 rises, a sufficient heat dissipating medium is provided on the metal cap 1 side of the substrate 3. Further, a white glass outer tube globe 5 with a diameter of 60mm having an in-line transmittance of 90% comprising the outer tube globe 5 shown in Figure 1 coated on the inner surface with fine silica powder was employed in all of the experimental lamps.
In order to conduct a parametric comparison of the zero-overlap areas, trial products were created in which the proportion of the zero-overlap area was varied with the radius of the abovementioned concentric circle. The number n of LED elements 4 was different, but all were lit as rated. Of course, as the number n of LED elements 4 increases, the total luminous flux of the completed lamp also increases. However, in the present experiment the total luminous flux was not unified, but was standardized using the number n of LED elements 4 (in other words a relative assessment was performed by dividing by W). Therefore with one element a power of 1W was supplied to the LED elements 4 (note that power losses are not considered in the calculation), and a power of 5W was supplied if there were five elements.
In order to compare efficiency, the total luminous flux of the experimental lamps was measured using an integrating sphere and was presented as a relative value, where 100% is defined as the theoretical efficiency (unit: lm/W) when the outer tube transmittance is 0.9 and the number of LED elements 4 employed is n, given by: rated output 100 (lm/element) x n (elements) / n (W) x 0.9 (outer tube transmittance).
Of course a high efficiency is preferable, and we considered at least 90% to be satisfactory. Further, non-uniform luminance on the outer tube globe 5 is called the luminance uniformity ratio, and it is preferable for the luminance to be uniform across all points, but unlike a bulb-shaped fluorescent lamp having a fluorescent lamp as the light source, realistically a uniform luminance cannot be achieved on the outer tube globe 5 since the light sources are very small and have a high luminance, and also have a light distribution angle. The degree of satisfaction felt by the user varies depending on how uniform this can be made.
Further, with relation to the directly-downward illumination intensity, the experimental lamps were lit with their bases upwards, and the illumination intensity 1m below the lamp was measured using an illuminometer, and a value was obtained by dividing the measured illumination intensity by the total wattage of the lamp. In other words, if the 4W directly-downward illumination intensity using four LED elements 4 is 521, then the directly-downward illumination intensity is defined as 52 / 4 = 13 (lx/W). Typically a directly-downward illumination intensity of at least 10 (lx/W) is satisfactory. This of course increases roughly in proportion to the total power consumption of the lamp if the design is the same, so in order for the user to obtain the required directly-downward illumination intensity, the user will either adjust the wattage of the bulb-shaped LED lamp (bulb-shaped LED light source 100) or adjust the number of lamps used.
In the embodiment, one LED element 4 was arranged in the middle of the substrate 5, but this need not necessarily be arranged in the middle. Further, the transmittance of the outer tube globe 5 is not limited to 90%, and the material may also be a resin rather than glass. The LED elements 4 were arranged on a concentric circle for the purposes of comparison.

[Explanation of the reference numbers]

1 Metal cap, 2 Cover, 3 Substrate, 4 LED element, 5 Outer tube globe, 6 Light diffusing layer, 7 Substantially spherical body, 100 Bulb-shaped LED light source, 200 Bulb-shaped LED light source, 201 Metal cap, 202 Cover, 203 Substrate, 204 LED element, 205 Outer tube globe, 206 Light diffusing layer, 207 Substantially spherical body.

Claims

A bulb-shaped LED light source(100) being a light source of a type that has a built-in lighting circuit and can be lit using a commercial power supply, emitting light over a range of approximately 2nSt (steradian), using LED (light emitting diode) elements(4) as a light source, having an electric bulb-shaped appearance, and not having a wide light distribution like that of an electric bulb, and being an alternative light source to an incandescent light bulb having an E or B metal cap (1), and further having an outer tube globe (5) in front of the LED light source in imitation of an incandescent light bulb,
wherein,
at least n, n is a natural number of 4 or more, abovementioned LED LED elements(4) are arranged within the abovementioned outer tube globe(5) on the same surface of a substantially planar substrate(3);
characterized in that,
each LED element(4) has a light distribution angle of at least 60° and 120° or less, and the central axis of the abovementioned light distribution angle is perpendicular to the surface of the abovementioned substantially planar substrate(3);
the light distribution areas inside the abovementioned light distribution angle within which each LED element illuminates light onto the inner surface of the abovementioned outer tube globe(5) are made to overlap;
and a part, including on the inner surface of the abovementioned outer tube globe(5) on the central axis of the lamp, of the abovementioned overlap comprises n overlapping abovementioned light distribution areas, and the n overlapping abovementioned light distribution areas comprise
at least 10% and no more than 80% of the inner surface of the abovementioned outer tube globe(5).
The bulb-shaped LED light source as claimed in claim 1, characterized in that the area not included in the light distribution area of any of the abovementioned LED elements(4) is less than 30% of the inner surface of the abovementioned outer tube globe(5).