The present invention relates to a lighting device. Background Art

With the development of LED illumination techniques, more and more people use an LED lighting device as a light source for applications to various environments. As for a lighting de ^¬ vice with a fixed light source, the characteristics of light emitted by the light source are generally set, for example, spectral power distribution, CCT, CRI, and so on. However, in many specific application environments such as hotels, malls, or residential buildings, it may be desired to tune the hue of the output light of the lighting device, espe ^¬ cially the CCT, to change the lighting atmosphere according to the need or the mood of people, for example, the lighting device emits a warm white light when a user spends his lei- sure time, while the lighting device emits a cool white light when a user studies and works.

In the prior art, a single color LED is generally provided, for example, a phosphor cover is provided for a blue LED to mix light. US 2009/0103293 Al discloses a lighting device, wherein a plurality of phosphor covers are provided for gen ^¬ erating emitted light with different CCT. In such a light ^¬ ing device an additional accommodation space needs to be pro ^¬ vided for part of unused phosphor covers, and the CCT is not uniform across the lighting surface or can merely be tuned non-continuously . US 7942540 B2 discloses an illumination device for mixing light for an LED with a phosphor cover, wherein the phosphor covers arranged alternatively are in ^¬ serted into the lighting device in the form of sidewalls to adjust the CC . However, such a lighting device needs a lar- ger accommodation part for the inserted phosphor covers, and the manufacturing and inserting processes are relatively com ^¬ plicate .

Summary of the Invention

In order to solve the technical problems above, the present invention provides a lighting device, which is easy to manu ^¬ facture and compact in structure and may obtain a uniform, continuous adjustable CCT on a lighting surface.

The lighting device according to the present invention comprises a circuit board with at least one LED chip mounted thereon, sidewalls extending from the circuit board, a phos ^¬ phor cover supported on the sidewalls, the circuit board, the phosphor cover, and the sidewall define a cavity accommodat ^¬ ing at least one LED chip, characterized in that, the light ^¬ ing device further comprises at least one optical member ar- ranged in the cavity, and the optical member has an adjust ^¬ able reflectivity to adjust the spectral power distribution of emitted light through the phosphor cover and/or the CCT of the emitted light.

The concept of the present invention lies in, instead of pro- viding a plurality of phosphor covers capable of realizing different light mixing effects to adjust the spectral power distribution and/or CCT, using an optical member in combination with one single phosphor cover to perform adjustment of the light through the phosphor cover. To be specific, at least part of light emitted by an LED chip and excited light generated by the phosphor cover are incident on the optical member, and the amount of light emitted by an LED chip and excited light generated by the phosphor cover, reflected by the optical member to the phosphor cover, is controlled by the adjustable reflectivity of the optical member. Thus, the proportion of light with different wavelengths emitted through the phosphor cover can be controlled, viz. the spectral power distribution and/or CCT of the emitted light can be controlled. In a preferred embodiment according to the present invention, the reflectivity of the optical member can be adjusted in a range from a full reflection state to a reflection state fi ^¬ nally to a non-reflection state. The optical members is con ^¬ sidered to be in the full reflecting state when its reflec- tivity is higher than 90% and in the non-reflecting state when its reflectivity is between 0% and 10%. In this way, the light incident on the optical member, especially the excited light, may be reflected, transmitted, or absorbed so as to realize the continuous adjustment of the CCT. Preferably, the reflectivity of the optical member in the reflection state is adjusted in a first range from 10% to 20% and in a second range from 80% to 90%.

In a preferred embodiment according to the present invention, the optical member has a plurality of regions, the plurality of regions having different reflectivities. Preferably, there are a plurality of the optical members, the plurality of the optical members having reflectivities different from each other.

In a preferred embodiment according to the present invention, the optical member is disposed on the circuit board and/or on inner surfaces of the sidewalls. The area where the excited light is reflected and transmitted is increased by increasing the area of the optical member, which may control and adjust the CCT of light from the lighting device more accurately.

In a preferred embodiment according to the present invention, the reflectivity of the optical member is adjusted by chang ^¬ ing a supply voltage of the optical member. The voltage ex ^¬ ternally applied to the optical member may be adjusted to ad ^¬ just the reflectivity of the optical member.

In a preferred embodiment according to the present invention, the optical member is electrically connected to the circuit board to receive a supply voltage. The circuit board of the lighting device may supply power for the optical member to adjust the supply voltage of the optical member, thereby ad ^¬ justing the reflectivity of the optical member according to different voltages.

In a preferred embodiment according to the present invention, the LED chip is a blue LED chip, a first part of blue light of the LED chip passes through gaps between phosphor particles of the phosphor cover and emerge, a second part of blue light interacts with the phosphor particles to produce yellow light, and a third part of blue light is incident on the cir ^¬ cuit board and/or the sidewalls. The first part of blue light emitted by the blue LED chip toward the phosphor cover does not interact with the phosphor particles and is emitted directly through the phosphor cover. The second part of blue light is interacted and mixed with the phosphor particles to form warm yellow light. The third part of blue light emitted by the blue LED chip may strike the circuit board and/or the sidewalls . In a preferred embodiment according to the present invention, a first part of yellow light of the yellow light generated by the second part of blue light emerge through the phosphor cover, and mixed with the emitted first part of blue light into white light. A second part of yellow light is reflected back to the inside of the enclosed cavity, for example, being reflected back to the circuit board and/or the sidewalls. The amount of third part of blue light and the amount of the second part of yellow right, which is reflected to the phos ^¬ phor cover, may be controlled via the optical member arranged on the circuit board and/or the sidewalls.

In a preferred embodiment according to the present invention, when the optical member is not in the non-reflection state, the second part of yellow light and the third part of blue light are at least partly reflected by the optical member to the phosphor cover. In said state, the optical member has the properties of a mirror and is capable of reflecting some ^¬ what the second part of yellow light and the third part of blue light according to the requirements of the application environments, allowing the light to be emitted through the phosphor cover.

In a preferred embodiment according to the present invention, the non-reflection state is full transmission state. Prefera ^¬ bly, the optical member is designed as a liquid crystal screen. The optical member may certainly be other devices with adjustable reflectivity, for example, a multilayered film or the like manufactured by an Mg-Ni alloy, compounds of transition metal elements or compounds of rare earth ele ^¬ ments. The optical member may be designed as a liquid crystal screen with optical characteristics, the light reflectivity of which is, for example, greater than 87% in a full reflec ^¬ tion state; the transmissivity of which is, for example, greater than 87% in a full transmission state; and the trans- missivity and reflectivity of which are, for example, both 43% in a translucence state.

In a preferred embodiment according to the present invention, when the optical member is in the full transmission state, the second part of yellow light and the third part of blue light pass through the optical member and are incident on the circuit board and/or the sidewalls. In said state, the opti ^¬ cal member has light transmission properties similar to glass, allowing the second part of yellow light and the third part of blue light to be transmitted directly through the op ^¬ tical member as much as possible to reach the sidewalls and/or the circuit board.

In a preferred embodiment according to the present invention, the side walls are made of a light absorbing material. The sidewalls may be, for example, formed of a black porous mate ^¬ rial or the sidewalls may be coated with a light absorbing coating, the second part of yellow light and the third part of blue light pass through the optical member and is incident on the sidewalls and are absorbed high efficiently. In a preferred embodiment according to the present invention, the non-reflection state is full absorption state. Prefera ^¬ bly, the optical member is made of any one of the Mg ₂ iHx, Mg ₂ CoHx and Mg ₂ FeHx. This can be achieved by choosing different material and choosing different power supply. In a preferred embodiment according to the present invention, when the optical member is in the full absorption state, the second part of yellow light and the third part of blue light are absorbed.

In a preferred embodiment according to the present invention, the optical member has a plurality of regions, and these re ^¬ gions have different reflectivities. For example, the re ^¬ flectivity of the area with the optical member provided on the inner surface of the sidewall may be different from that of the area with the optical member provided on the circuit board. Thus, the desired optical effect may be obtained.

Brief Description of the Drawings

The accompanying drawings constitute a part of the present Description and are used to provide further understanding of the present invention. Such accompanying drawings illustrate the embodiments of the present invention and are used to de ^¬ scribe the principles of the present invention together with the Description. In the accompanying drawings the same components are represented by the same reference numbers. As shown in the drawings:

Fig. 1 is a view of a first embodiment of a lighting device according to the present invention in cross-section, wherein the optical member is in a full reflection state;

Fig. 2 is a view of a second embodiment of a lighting device according to the present invention, wherein the optical member is in a non-reflection state; and

Fig. 3 is a wavelength-radiation power diagram of a lighting device according to the present invention in the case where merely the reflectivity of the optical member mounted on the circuit board is changed and other conditions are the same.

Detailed Description of the Embodiments

Fig. 1 is a view of a first embodiment of a lighting device according to the present invention in cross-section. As shown, the lighting device may be, for example, in the form of cylinder, cuboid or cube, comprising a phosphor cover 3 as a top surface, a circuit board 2 as a bottom surface and sidewalls 4 defining a cavity R with the phosphor cover 3 and the circuit board 2. In the enclosed cavity R, at least one blue LED chip 1 is mounted on the circuit board, the LED chip 1 emits a first part of blue light Bl and a second part of blue light B2 toward the phosphor cover 3, and the LED chip 1 further emits a third part of blue light B3 toward the side- walls 4. In the lighting device according to the present in ^¬ vention, the phosphor cover 3 is formed of a light transmis- sive material such as PC, PMMA, doped with phosphor particles 6; and the sidewalls 4 are made of a light absorbing mate- rial, for example made of a black porous material, or the sidewalls 4 may be coated with a light absorbing coating.

In order to realize the control of the CCT of the lighting device, viz. controlling and adjusting the spectral power distribution of the emitted light passing through the phos- phor cover 3, an optical member 5 with adjustable reflectivity is provided at one side facing the enclosed cavity R of the sidewalls 4 and/or the circuit board 2 in the present in ^¬ vention. Preferably, around the LED chip 1 on the circuit board 2 there is mounted such optical member 5, which is, for example, a liquid crystal screen with optical characteris ^¬ tics. Such optical member 5 is electrically connected to the circuit board 2 and the reflectivity of the optical member 5 is adjusted by providing different voltages via the circuit board 2, for example, gradually adjusting from a full reflec- tion state to a non-reflection state. The optical member 5 is considered to be in the full reflecting state when the re ^¬ flectivity of the optical member 5 is between 90% and 100% ; The optical member 5 is considered to be in the non- reflection state when the reflectivity of the optical member 5 is between 0% and 10% _o The reflectivity of the optical mem ^¬ ber 5 in the reflection state may be adjusted between a first range from 10% to 20% and a second range from 80% to 90%. In this embodiment, the first range from 10% to 20% may be con ^¬ sidered to be one low reflectivity range and the second range from 80% to 90% may be considered to be one high reflectivity range . Fig. 1 illustrates a first embodiment of the lighting device according to the present invention when the optical member 5 is in a full reflection state. The first part of blue light Bl of the blue LED chip 1 passes directly through gaps be ^¬ tween the phosphor particles 6 of the phosphor cover 3 to be emitted outward, therefore, the emitted light does not acti ^¬ vate the phosphor particles 6 to generate yellow light but remains as blue light; meanwhile, the second part of blue light B2 of the blue LED chip 1 is also emitted into the phosphor cover 3, however, different from the first part of blue light 1, the second part of blue light B2 activates the phosphor particles 6 to generate yellow light. A first part of yellow light Yl generated passes through the phosphor cover 3 to be emitted outward and mixed with the first part of blue light Bl to form white light, while the second part of yellow light Y2 is reflected back to the inside of the en ^¬ closed cavity R and strike directly the optical member 5 pro ^¬ vided on the sidewall 4 and/or the circuit board 2. The LED chip 1 further emits the third part of blue light B3 directly striking the sidewalls 4 and the third part of blue light B3 occupied a small portion of total blue light. Since the op ^¬ tical member 5 is adjusted herein to a reflection state by a control voltage outputted by the circuit board 2, the optical member 5 may be regarded as a mirror. The optical member 5 reflects the second part of yellow light Y2 and the third part of blue light B3 with a reflectivity of, for example, greater than 85 %. Therefore, the effect of almost full re ^¬ flection may be realized in the cavity R, and a large amount of yellow light is finally reflected and is emitted outward after passing through the phosphor cover 3 substantially without loss, such that the proportion of the yellow light in the final emitted light is relatively high so as to obtain a relatively low CCT .

Fig. 2 is a view of a second embodiment of a lighting device according to the present invention when the optical member 5 is in a non-reflection state. The optical member 5 is gradu- ally adjusted via the control voltage outputted by the cir ^¬ cuit board 2 to a translucence state and finally adjusted to a non-reflection state as shown by Fig. 2. Herein, the optical member 5 has, for example, a transmissivity of greater than 84%, thus, the optical member 5 may be approximately re- garded as light transmissive glass. The second part of yel ^¬ low light Y2 and the third part of blue light B3, passing through the surface of the optical member 5, are further emitted to the circuit board 2 or to the sidewall 4 behind the optical member 5, almost without reflection and block. Based on the light absorbing property of the sidewalls 4, the third part of blue light B3 and the second part of yellow light Y2 are almost fully absorbed. In this case, a large amount of the yellow light is absorbed and cannot be emitted, such that the proportion of the yellow light in the emitted light is relatively low, thereby obtaining a relatively high CCT.

In this embodiment, the optical member 5 may alternatively be in the full absorption state. The third part of blue light B3 and the second part of yellow light Y2 are almost fully ab ^¬ sorbed by the optical member 5 directly, through the adjust ^¬ ing of the control voltage of the optical member 5. Prefera- bly, the optical member is made of any one of the Mg ₂ iHx, Mg ₂ CoHx and Mg ₂ FeHx.

Certainly, during the adjustment process of the optical mem ^¬ ber 5 from the full reflection state to the translucence state finally to the non-reflection state, the second part of yellow light Y2 is absorbed more and more, whereby the CCT of the white light generated by the lighting device through mix ^¬ ing light may be continuously adjusted and controlled accord ^¬ ing to requirements of actual applications. In addition, the optical member 5 has a plurality of regions, and these re ^¬ gions have different reflectivities. For example, the re ^¬ flectivity of the area with the optical member 5 provided on the inner surface of the sidewall 4 may be different from that the reflectivity of the area with the optical member 5 provided on the circuit board 2. Thus, the desired optical effect may be obtained.

Fig. 3 is a wavelength-radiation power diagram of a lighting device according to the present invention in which the reflectivity of the optical member 5 mounted on the circuit board 2 is adjusted. The test result is based on a T8 tube. What is represented by a dotted line is an emitting spectrum when the optical member 5 mounted on the circuit board 2 is in a low reflection state (the reflectivity is about 80%) , wherein the CCT is 5507K and the CRI is 89. What is repre ^¬ sented by a solid line is an emitting spectrum when the opti- cal member 5 mounted on the circuit board 2 is in a high re ^¬ flection state (the reflectivity is about 99%) , wherein the CCT is 5053K and the CRI is 87.2. As may be seen from said diagram, since the wavelength of the blue light is generally between 420 to 480 nm and the wave ^¬ length of the yellow light is generally between 500 to 680 nm, the peak region on the left side of the diagram repre ^¬ sents the blue light part, and the peak region on the right side of the diagram represents the yellow light part. When the reflectivity of the optical member is increased, the blue light peak is increased by 10%, and the yellow light peak is increased by 25%. And the width of the spectral line of yellow light is greater than the width of the spectral line of blue light, thus, the CCT of the emitted light will be lowered .

The above is merely preferred embodiments of the present in ^¬ vention but not to limit the present invention. For the per ^¬ son skilled in the art, the present invention may have vari ^¬ ous alterations and changes. Any alterations, equivalent substitutions, improvements, within the spirit and principle of the present invention, should be covered in the protection scope of the present invention.

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List of reference signs

1 LED chip

2 circuit board

3 phosphor cover

4 sidewalls

5 optical member

6 phosphor particles

R cavity

Bl first part of blue light

B2 second part of blue light

B3 third part of blue light

Yl first part of yellow light

Y2 second part of yellow light