Light emitting device and driving method thereof

A driving method of a light emitting device including visible light emitting elements is provided. In a first visible light communication mode, a first portion of the visible light emitting elements is driven and a second portion of the visible light emitting elements is idled for the first portion of the visible light emitting elements having a first current density. In a second visible light communication mode, each of the visible light emitting elements is driven so as to have a second current density. An illumination brightness difference of the light emitting device between the first visible light communication mode and the second visible light communication mode is smaller than 15%.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan application serial no. 104138846, filed on Nov. 23, 2015. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND OF THE DISCLOSURE

1. Field of the Disclosure

The disclosure relates to a light emitting device and a driving method thereof.

2. Description of Related Art

Application of solid-state light emitting elements such as light emitting diodes (LEDs) has become increasingly widespread, all such as the light source modules of display panels, the lighting devices used in everyday life, the indicating lights in public spaces are becoming more and more common to employ the light emitting diodes (LEDs) as a light source. In addition, along with the rapid development of communication technology, light emitting diodes are also employed in the application of wireless signal transmission, especially, the light emitting diodes used for illumination can be applied in technology of visible light communication (VLC).

The light emitting diodes of this sorts of solid-state light emitting elements have the advantages of low power consumption, fast response, long life, suitable for mass production, etc., so quite suitable for being applied to the light emitting devices for lighting. However, if these sorts of light emitting devices are to be applied in the visible light communication, many requirements are still required. For instance, in general, the dimensions of the light emitting diodes of the light emitting devices for lighting are comparatively larger. Taking a square light emitting diode as an example, the side length thereof may be several millimeters (mm). Therefore, the generated parasitic capacitance due to the dimension of the light emitting diode itself comparatively larger, and it may affect the signal transmission efficiency. In addition, if the operating current of the light emitting diode is increased in order to improve the signal modulation bandwidth, then it would apt to the shortened lifetime and poor stability of the components due to the heat accumulation. Therefore, it is not easy to use the light emitting devices for lighting as visible light communication media.

SUMMARY OF THE DISCLOSURE

The driving method of light emitting device of the disclosure may used for driving a light emitting device including a plurality of visible light emitting elements. In a first visible light communication mode, a first portion of the visible light emitting elements is driven and a second portion of the visible light emitting elements is idled, such that the first portion of the visible light emitting elements has a first current density. In a second visible light communication mode, each of the visible light emitting elements is driven so that each of the visible light emitting elements has a second current density, and the first current density is larger than the second current density. The illumination brightness difference of the light emitting device between the first visible light communication mode and the second visible light communication mode is smaller than 15%.

The light emitting device of the disclosure includes a plurality of first visible light emitting elements and a plurality of second visible light emitting elements. Each of the first visible light emitting elements has a first illumination area, and each of the second visible light emitting elements has a second illumination area. The first illumination area is smaller than the second illumination area, and the first visible light emitting elements and the second visible light emitting elements are arranged side by side. In the first visible light communication mode, the first visible light emitting elements are driven and the second visible light emitting elements are idled. In the second visible light communication mode, each of the first visible light emitting elements and the second visible light emitting elements is driven. The illumination brightness difference of the light emitting device between the first visible light communication mode and the second visible light communication mode is smaller than 15%.

The light emitting device of the disclosure includes a plurality of first visible light emitting elements and a plurality of second visible light emitting elements. Each of the first visible light emitting elements has a first current carrying capacity. Each of the second visible light emitting elements has a second current carrying capacity. The first current carrying capacity is larger than the second current carrying capacity, and the first visible light emitting elements and the second visible light emitting elements are arranged side by side. In the first visible light communication mode, the first visible light emitting elements are driven and the second visible light emitting elements are idled. In the second visible light communication mode, each of the first visible light emitting elements and the second visible light emitting elements is driven. The illumination brightness difference of the light emitting device between the first visible light communication mode and the second visible light communication mode is smaller than 15%.

DESCRIPTION OF THE EMBODIMENTS

FIG. 1is a schematic view of a light emitting device according to an exemplary embodiment of the disclosure. As shown inFIG. 1, the light emitting device100includes a plurality of visible light emitting elements110, and the visible light emitting elements are arranged side by side. In the embodiment, the visible light emitting elements110are arranged in an array of 6 rows and 4 columns, but in other embodiments the array may be composed of a different number of rows and columns. The so-called arranging side by side in the disclosure is not limited to that the components are arranged in two directions perpendicular to each other. In particular applications, the plurality of visible light emitting elements110may be arranged along tracks such as concentric circles, radial, Z shape, and so on. In other words, arranged side by side in the disclosure means that the visible light emitting elements110are arranged in a manner of not blocking each other's light emitting surface.

In the embodiment, each of the visible light emitting elements110is a visible light emitting diode adapted to emit a light with the visible light wavelength range, for example the wavelength is between 400 nm and 700 nm, however may also emit a light beyond the visible wavelength range, such as infrared light wavelength range. The visible light emitting elements110are semiconductors specifically, the material thereof includes Group III elements, Group V elements, and so on. The visible light emitting elements110may also be solid-state light emitting elements. In addition, in the disclosure, the dimensions or the illumination areas of the visible light emitting elements110may be different. The illumination area of each visible light emitting element110may be determined by the semiconductor material of LED dies, and it is not necessarily complete. In some embodiments, each of the visible light emitting elements110may be constituted by an LED die having a plurality of mesa structures, and the illumination areas of the visible light emitting elements110are determined by these mesas.

FIG. 2Ais a schematic view of the light emitting device ofFIG. 1in the first visible light communication mode. Referring toFIG. 2A, the visible light emitting elements110of the light emitting device100may be divided into a plurality of groups U, wherein each group U includes four visible light emitting elements110, and respectively numbered as visible light emitting elements110A, visible light emitting elements110B, visible light emitting elements110C, and visible light emitting elements110D. In the disclosure, the driven visible light emitting elements110are shown with thin-dot-filled patterns.

As shown inFIG. 2A, in the first visible light communication mode, merely a portion (called first portion) of the visible light emitting elements110are driven and another portion (called second portion) of the visible light emitting elements110are idled. Specifically, in each group U ofFIG. 2A, in the first visible light communication mode, the visible light emitting elements110A are driven and taken as the first portion of the visible light emitting elements110. Similarly, in the first visible light communication mode, the visible light emitting elements110B,110C,110D of each group U are idled and taken as the second portion of the visible light emitting elements110. In this time, each of the first portion of the visible light emitting elements110, i.e., each of the visible light emitting elements110A of each group U, has a first current carrying capacity. In addition, in the first visible light communication mode, the light emitting device100emits light through the driven visible light emitting elements110A.

The larger the current density of the light emitting device100, the larger the signal transmission bandwidth in the application of light communication may be provided. In the embodiment, since the visible light emitting elements110driven in the first visible light communication mode has a larger first current density, the visible light emitting elements110driven in the first visible light communication mode may provide a larger bandwidth in transmission signal. Therefore, the light emitting device100not only may provide lighting function, but also may provide a signal transmission function with a high bandwidth, thereby serving as a device capable of both lighting and light communication. In addition, in the second visible light communication mode, although the current density of the visible light emitting elements110are comparatively lower, the light emitting device100may perform signal transmission for providing light communication function depending on the circumstances. Namely, no matter whichever the light communication mode is, the light emitting device100may provide a light communication function, and the light emitting device100has the first signal transmission bandwidth in the first visible light communication mode which is larger than the second signal transmission bandwidth in the second visible light communication mode.

In the first visible light communication mode, the light emitting device100is not limited to emit light by driving the visible light emitting elements110A as shown inFIG. 2A. For example,FIG. 2BthroughFIG. 2Dare schematic views showing various embodiments of the light emitting device in the first visible light communication mode, and the reference number of each component shown inFIG. 2BthroughFIG. 2Dis the same as that shown inFIG. 2A. InFIG. 2B, in the first visible light communication mode, the light emitting device100may drive the visible light emitting elements110B of each group U, and such that the visible light emitting elements110A,110C,110D of each group U are idled. InFIG. 2C, in the first visible light communication mode, the light emitting device100may drive the visible light emitting elements110C of each group U, and such that the visible light emitting elements110A,110B,110D of each group U are idled. InFIG. 2C, in the first visible light communication mode, the light emitting device100may drive the visible light emitting elements110D of each group U, and such that the visible light emitting elements110A,110B,110C of each group U are idled. Overall, in the light emitting device100, as long as a portion of the visible light emitting elements110are driven and a portion of the visible light emitting elements110are idled, this mode is taken as the first visible light communication mode mentioned in the disclosure. For instance, in the first visible light communication mode, inFIG. 2AthroughFIG. 2D, for four visible light emitting elements110of each group U, there may be two of them being driven and another two of them being idled, or three of them being driven and another one of them being idled.

For instance,FIG. 2EtoFIG. 2Fare schematic views of the light emitting device ofFIG. 1in the first visible light communication mode. InFIG. 2EtoFIG. 2F, the visible light emitting elements110of the light emitting device100are divided into a plurality of groups U1to U6, and each of the groups U1to U6includes four visible light emitting elements110. In the first visible light communication mode, the visible light emitting elements110of at least one group among the groups U1to U6are driven while the visible light emitting elements110of other groups are idled in the light emitting device100. TakingFIG. 2Eas an example, the first visible light communication mode is shown as the visible light emitting elements110of the group U1are driven while the visible light emitting elements110of the groups U2to U6are idled. TakingFIG. 2Fas an example, the first visible light communication mode is shown as the visible light emitting elements110of the group U2are driven while the visible light emitting elements110of the groups U1and U3to U6are idled. In other embodiments, the first visible light communication mode may be the visible light emitting elements110of the group U3being driven while the visible light emitting elements110of the groups U1, U2and U4to U6being idled, the visible light emitting elements110of the group U4being driven while the visible light emitting elements110of the groups U1to U3, U5, U6being idled, the visible light emitting elements110of the group U5being driven while the visible light emitting elements110of the groups U1to U4and U6being idled, or the visible light emitting elements110of the group U6being driven while the visible light emitting elements110of the groups U1to U5being idled. In other words, in the first visible light communication mode, the driven visible light emitting elements110may be concentratedly arranged as shown inFIG. 2EandFIG. 2F, and alternatively, the driven visible light emitting elements110may be separately disposed and not concentratedly arranged as shown inFIG. 2AthroughFIG. 2D. No matter whichever way the first visible light communication mode is performed, the visible light emitting elements110driven in this mode are taken as the first portion while the visible light emitting elements110idled are taken as the second portion.

FIG. 3is a schematic view of the light emitting device ofFIG. 1in the second visible light communication mode. Referring toFIG. 3, in the second visible light communication mode, each of the visible light emitting elements110is driven, such that each of the visible light emitting elements110has a second current density. In this time, the illumination brightness of the light emitting device100is emitted by all of the visible light emitting elements110.

In the embodiment, no matter in the first visible light communication mode or in the second visible light communication mode, the same rated current may be input to the light emitting device100. In this time, in the first visible light communication mode shown in any ofFIG. 2AthroughFIG. 2F, only a portion of the visible light emitting elements110are driven while all of the visible light emitting elements110are driven in the second visible light communication mode shown inFIG. 3. Therefore, the first current density of each visible light emitting element110driven in the first visible light communication mode is larger than the second current density of each visible light emitting element110driven in the second visible light communication mode. For example, in the first visible light communication mode, the first current density of the driven visible light emitting elements110may be larger than 70 A/cm2. In comparison, in the second visible light communication mode, the second current density of each of the driven visible light emitting elements110may be smaller than 70 A/cm2.

The whole illumination area of the visible light emitting elements110driven in the first visible light communication mode is smaller than the whole illumination area of the visible light emitting elements110driven in the second visible light communication mode. Nevertheless, under different current densities, the illumination brightness of a single visible light emitting element110driven in the first visible light communication mode may be larger than the illumination brightness of a single visible light emitting element110driven in the second visible light communication mode. Therefore, for the overall light emitting device100, when operated under two different light communication modes, the illumination brightness of the light emitting device100may substantially be the same.

For example, the illumination brightness difference of the light emitting device100between the first visible light communication mode and the second visible light communication mode is smaller than 15%. In other words, if the illumination brightness of the light emitting device100in the first visible light communication mode is X and the illumination brightness of the light emitting device100in the second visible light communication mode is Y, then the illumination brightness difference of the light emitting device100between the first visible light communication mode and the second visible light communication mode is V=(X−Y)/X, wherein |V|<15%, or |V|<10%, or even |V|<5%. In addition, the illumination wavelength difference of the light emitting device100between the first visible light communication mode and the second visible light communication mode is smaller than 2 nm, or even smaller than 1 nm. Therefore, even though alternately operated in these two visible light communication modes, the light emitting device100may still provide a stable illumination brightness, the users may not feel that the illumination brightness of the light emitting device100changes due to different driving modes. Accordingly, in the case that the light emitting device100is applied in the lighting field, it is unlikely to occur flickering problem.

In the embodiment, the visible light emitting elements110with current carry capacity sufficient to withstand the first current density may be driven in the first visible light communication mode and provides dual function of both lighting and visible light communication. If the visible light emitting elements110A of each group U are the only ones having a larger current carrying capacity sufficient to withstand the first current density, then every time when the first visible light communication mode is performed, the performing way shown inFIG. 2Awill be performed. However, in a case that all of the visible light emitting elements110of the light emitting device100have sufficient current carrying capacity, the light emitting device100may choose any one of the performing ways to perform the first visible light communication mode. In addition, in a case that the light emitting device100repeatedly performs the first visible light communication mode a plurality of times, then different portions of the visible light emitting elements110may be driven in the first visible light communication mode when performed at different times. For example, in the actual operation of the light emitting device100, first any one of the performing ways shown inFIG. 2AthroughFIG. 2Dmay be performed in the first visible light communication mode, next another way of the performing ways shown inFIG. 2AthroughFIG. 2Dmay be performed in the first visible light communication mode. As such, in the first visible light communication mode which is performed at different times, different visible light emitting elements110may be driven, facilitating the light emitting device100to slow down the phenomenon of aging or damage due to long-term use. In other words, the alternately driving different visible light emitting elements110in the first visible light communication mode performed at different times may facilitate to extend the life-time of the light emitting device100and improve the reliability of the light emitting device100.

FIG. 4Ais a schematic flowchart of a driving method of a light emitting device according to an exemplary embodiment of the disclosure. Referring toFIG. 4A, the driving method of the embodiment may be used for driving the light emitting device100ofFIG. 1or any kind of light emitting device of the disclosure. The driving method of the disclosure includes alternately performing the step10and the step20. The step10is the step which performs the first visible light communication mode and the signal transmission. In this time, any driving method ofFIG. 2AthroughFIG. 2For other similar driving methods may be used for driving the light emitting device100. In the step10, only a portion of the visible light emitting elements110are driven while the other portion of the light emitting elements110are idled. When the light emitting device100is operated by a rated current, the driven visible light emitting elements110have a larger current density, and a signal transmission with a higher bandwidth may be provided. The step20is the step which performs the second visible light communication mode. At this time, all of the visible light emitting elements110are performed, namely the method shown inFIG. 3is used to operate the light emitting device100. In the second visible light communication mode, since the driven visible light emitting elements110have a smaller current density, signal transmission may not be performed in the step20. In other words, in one embodiment, along with the light emitting device100emitting light, it is possible to select to perform signal transmission only in the period when the first visible light communication mode is performed. In addition, when the step10is repeatedly performed, it is possible that different visible light emitting elements110of the light emitting device100are driven, optionally, so as to reduce the possibility of early damage of the visible light emitting elements110.

FIG. 4Bis a schematic flowchart of a driving method of a light emitting device according to an exemplary embodiment of the disclosure. Referring toFIG. 4B, the driving method of the embodiment may be used for driving the light emitting device100ofFIG. 1, and including alternately performing the step12and the step22. The step12is the step which performs the first visible light communication mode and the first signal transmission. In this time, any driving method ofFIG. 2AthroughFIG. 2For other similar driving methods may be used for driving the light emitting device100. In the step12, only a portion of the visible light emitting elements110are driven while the other visible light emitting elements110are idled, thus the driven visible light emitting elements110has a higher current density, and may provide the first signal transmission. In addition, the step22is the step which performs the second visible light communication mode and the second signal transmission, for example, the method shown inFIG. 3is used for driving the light emitting device100, that is all the of the visible light emitting elements110are driven. Under the operation of the rated current, the current density of the driven visible light emitting elements110is smaller compared to that of the first visible light communication mode. Therefore, the second signal transmission performed in the step22has a smaller bandwidth. In other words, in the embodiment, the light emitting device100may also perform signal transmission while emitting light, but the first signal transmission bandwidth of the first signal transmission performed in the first visible light communication mode is larger than the second signal transmission bandwidth of the second signal transmission performed in the second visible light communication mode. In one embodiment, the visible light emitting elements110which perform the second signal transmission in the second visible light communication mode may be the same as the visible light emitting elements110which perform the first signal transmission in the first visible light communication mode. Alternatively, in one embodiment, it is selectable that the visible light emitting elements110which perform the first signal transmission in the first visible light communication mode do not perform signal transmission in the second visible light communication mode, but only provides lighting function. In addition, when the step12is repeatedly performed, it is possible that different visible light emitting elements110of the light emitting device100are driven, optionally, so as to reduce the possibility of early damage of the visible light emitting elements110.

FIG. 5is a schematic view of a light emitting device according to another exemplary embodiment of the disclosure. Referring toFIG. 5, the light emitting device200includes a plurality of first visible light emitting elements212and a plurality of second visible light emitting elements214, and the first visible light emitting elements212and the second visible light emitting elements214are arranged side by side. Each of the first visible light emitting elements212has a first light emitting layer, each of the second visible light emitting elements214has a second light emitting layer, and a material of the first light emitting layer is different from a material of the second light emitting layer. For example, the illumination wavelength of the first light emitting layer of the first visible light emitting elements212is in an infrared light wavelength range. In the embodiment, each of the first visible light emitting elements212has a first illumination area A1, each of the second visible light emitting elements214has a second illumination area A2, and the first illumination area A1is smaller than the second illumination area A2. Specifically, the first illumination area A1is a polygonal area, and the side length L1of the first illumination area A1is, for example, larger than or equal to 5 μm and smaller than 1 mm. The second illumination area A2may also be a polygonal area, and the side length L2of the second illumination area A2may be several times of the side length L1. The light emitting device200may use the driving method similar to the driving method of the light emitting device100for driving, so as to provide a lighting function and a signal transmission function. In other words, the light emitting device200uses any method shown inFIG. 4AandFIG. 4Bfor driving.

Specifically, the light emitting device200may use two modes for driving, for example, the first visible light communication mode and the second visible light communication mode.FIG. 6Ais a schematic view of the light emitting device ofFIG. 5in the first visible light communication mode, andFIG. 6Bis a schematic view of the light emitting device ofFIG. 5in the second visible light communication mode. As shown inFIG. 6A, in the first visible light communication mode, only the first visible light emitting elements212are driven, while the second visible light emitting elements214are idled in the light emitting device200. As shown inFIG. 6B, in the second visible light communication mode, each of the first visible light emitting elements212and the second visible light emitting elements214is driven.

In the first visible light communication mode, each visible light emitting element212has a first current density, and in the second visible light communication mode, each of the first visible light emitting elements212and the second visible light emitting element214has a second current density. In addition, the first current density is larger than the second current density. Therefore, the illumination brightness of a single first visible light emitting element212driven in the first visible light communication mode may be larger than the illumination brightness of a single first visible light emitting element212driven in the second visible light communication mode. Nevertheless, the whole illumination area of the first visible light emitting elements212and the second visible light emitting elements214driven in the second visible light communication mode is larger than the whole illumination area of the first visible light emitting elements212driven in the first visible light communication mode. Therefore, the illumination brightness difference of the light emitting device200between the first visible light communication mode and the second visible light communication mode is smaller than a degree that the users may feel. In other words, in either of the visible light communication modes, the light emitting device200may provide a substantially equal rated output power.

In the embodiment, the description that the illumination brightness difference of the light emitting device200between the first visible light communication mode and the second visible light communication mode is smaller than a degree that the users may feel means that, the illumination brightness difference of the light emitting device200between the first visible light communication mode and the second visible light communication mode is smaller than 15%. In other words, if the illumination brightness of the light emitting device200in the first visible light communication mode is X and the illumination brightness of the light emitting device200in the second visible light communication mode is Y, then the illumination brightness difference of the light emitting device200between the first visible light communication mode and the second visible light communication mode is V=(X−Y)/X, wherein |V|<15%, or |V|<10%, or even |V|<5%. In addition, the illumination wavelength difference of the light emitting device200between the first visible light communication mode and the second visible light communication mode is smaller than 2 nm, or even smaller than 1 nm.

In addition, in the first visible light communication mode, since the first density current of the first visible light emitting elements212is larger, the light emitting device200may provide a higher signal transmission bandwidth when performing signal transmission. In the second visible light communication mode, the signal transmission bandwidth provided by the light emitting device200may be comparatively lower. Therefore, when using the driving method ofFIG. 4Ato drive the light emitting device200, the light emitting device200may provide signal transmission function with a high bandwidth only in the first visible light communication mode. When using the driving method ofFIG. 4Bto drive the light emitting device200, the light emitting device200may alternately provide signal transmission function with a high bandwidth and signal transmission function with a low bandwidth during performing the lighting function. As such, the light emitting device200may be operated according to different requirements.

FIG. 6Cis a schematic view showing another embodiment of the light emitting device ofFIG. 5in the first visible light communication mode. InFIG. 6C, the light emitting device200may drive only a portion of the first visible light emitting elements212, and other portion of the first visible light emitting elements212and all of the second visible light emitting elements214are idled, in the first visible light communication mode. Additionally, when the first visible light communication mode is performed at different times, different first visible light emitting elements212may be driven. In other words, the first visible light emitting elements212may be driven in turn in the first visible light communication mode at different times. As such, the life time of the first visible light emitting elements212may be unlikely to decrease due to excessively frequent operating in high current density, for example, early damage is unlikely to occur.

In the embodiment ofFIG. 5, the arranging way of the first visible light emitting elements212and the second visible light emitting elements214is that, the second visible light emitting elements214are located at the center, and the first visible light emitting elements212surround the second visible light emitting elements214. However, the arranging way of the components of the disclosure is not limited. For example,FIG. 7is a schematic view of a light emitting device according to another exemplary embodiment of the disclosure. InFIG. 7, the light emitting device300includes a plurality of first visible light emitting elements312and a plurality of second visible light emitting elements314, wherein every four of the first visible light emitting elements312are arranged in 2×2 to form a group G, and the second visible light emitting elements314and the groups G are arranged alternately. The light emitting device300uses any method shown inFIG. 4AandFIG. 4Bfor driving. Specifically, in the first visible light communication mode, only a portion of the first visible light emitting elements312may be driven, and in the second visible light communication mode, all of the first visible light emitting elements312and all of the second visible light emitting elements314may be driven.

In the embodiments ofFIG. 5andFIG. 7, the first current carrying capacity of the first visible light emitting elements212and312may be larger than the second current carrying capacity of the second visible light emitting elements214and314. Therefore, the first visible light emitting elements212and312may be driven in the first visible light communication mode, and may not lead to damage due to the excessively high current density.

In the abovementioned embodiment, any one of the light emitting devices100through300may provide white light and is applicable in lighting field. At this time, a single visible light emitting element may include at least one light emitting diode chip and phosphor matched with the illumination wavelength of the light emitting diode chip. For example, the blue light emitting diode chip matched with yellow phosphor, or yellow-green phosphor. Alternatively, the blue light emitting diode and the red light emitting diode matched with yellow phosphor, or yellow-green phosphor. In addition, a single visible light emitting element may be composed of a plurality of light emitting diode chips optionally without phosphor. If the visible light emitting element includes a plurality of light emitting diode chips, the light emitting diode chips have different illumination wavelength ranges, thereby facilitating providing more kinds of signal transmission.

FIG. 8is a schematic view of the transmission signals of a light emitting device according to an exemplary embodiment of the disclosure. Referring toFIG. 8, each of the visible light emitting elements of the light emitting device includes three light emitting diode chips, and the three light emitting diode chips may be driven respectively. When the three light emitting diode chips emit different wavelength ranges respectively, the light of different light emitting diode chips may be distinguished due to the different wavelength ranges. In addition, when the illumination brightness or the switching frequencies during transmission of different light emitting diode chips are different, the light of different light emitting diode chips may also be distinguished. Therefore, the different light emitting diode chips may respectively provide corresponding channels for transmitting the first signal SG1, the second signal SG2and the third signal SG3.

In the four time sequences I, II, III and IV shown inFIG. 8, each of the time sequences I, II, III and IV may be divided into two time periods and each of the time sequences I, II, III and IV is not more than one sixtieth of a second, wherein one is for providing lighting function while the other one is for providing signal transmission function. In one embodiment, in the time period I-1, II-1, III-1or IV-1, the visible light emitting element may provide lighting function, while in the time period I-2, II-2, III-2or IV-2, the visible emitting element may provide signal transmission function. However, in other embodiments, the time period for providing signal transmission function may be earlier than the time period for providing lighting function. In addition, the first signal SG1, the second signal SG2and the third signal SG3are independent to each other, thus at least in the time period for providing signal transmission function, the first signal SG1, the second signal SG2and the third signal SG3may be synchronized with each other, not synchronized with each other, or partially synchronized with each other.

For instance, the first signal SG1has low level, low level, high level and high level in the time periods I-2, II-2, III-2and IV-2, respectively. The second signal SG2has high level, low level, high level and low level in the time periods I-2, II-2, III-2and IV-2, respectively. The third signal SG3has low level, high level, low level and high level in the time periods I-2, II-2, III-2and IV-2, respectively. As such, if the low-level bit information for transmitting is 0 and the high-level bit information for transmitting is 1, then the first signal SG1in the time sequences I to IV respectively transmits bit information of 0, 0, 1, 1, the second signal SG2in the time sequences I to IV respectively transmits bit information of 1, 0, 1, 0, and the third signal SG3in the time sequences I to IV respectively transmits bit information of 0, 1, 0, 1. In other embodiments, signals of different frequencies may be used and respectively transmits different bit information, and no need to distinguish the kind of the bit information desired to be transmitted by high level or low level. As such, the light emitting device may provide more channels to perform signal transmission, and signal transmission operation of different channels may be independently performed without affecting each other, thereby facilitating to realize multifunction technology.

In light of the foregoing, the driving method of the light emitting device of the embodiment of the disclosure includes the first visible light communication mode and the second visible light communication mode. The first visible light communication mode merely drives a portion of the visible light emitting elements and the driven visible light emitting elements have a larger current density. The second visible light communication mode merely drives all of the visible light emitting elements and the driven visible light emitting elements have a smaller current density. As such, in the first visible light communication mode, the light emitting device may provide signal transmission function with a higher bandwidth while providing lighting function at the same time. In the second visible light communication mode, the light emitting device may also provide signal transmission function with a lower bandwidth while providing lighting function at the same time. Therefore, the light emitting device of the disclosure has dual function which may take care of both lighting function and light communication function. Moreover, when the first visible light communication mode is performed at different times, different visible light emitting elements of the light emitting device of the disclosure may be driven in turn, facilitating to slow down the phenomenon of aging or damage of the visible light emitting elements due to driven in high current density. Therefore, the light emitting device of the disclosure has an ideal service life and reliability. Furthermore, the visible light emitting elements of the light emitting device may include a plurality of light emitting chips, and the light emitting chips may be operated independently and provide a plurality of transmission channels so as to achieve multifunction technology.