Light emitting device for AC power operation
View Patent ↗Disclosed is an improved light-emitting device for an AC power operation. An AC light-emitting device according to the present invention employs a variety of means by which light emission time is prolonged during a ½ cycle in response to a phase change of an AC power source and a flicker effect can be reduced. For example, the means may be switching blocks respectively connected to nodes between the light emitting cells, switching blocks connected to a plurality of arrays, or a delay phosphor. Further, there is provided an AC light-emitting device, wherein a plurality of arrays having the different numbers of light emitting cells are employed to increase light emission time and to reduce a flicker effect.
1. A light emitting device, comprising:
a light emitting diode (LED) chip comprising a plurality of light emitting cells electrically connected in series, in parallel, or in series-parallel; and
a transparent member covering the LED chip, the transparent member comprising a first phosphor and a second phosphor,
wherein the first phosphor is a delay phosphor configured to be excited by light emitted from the light emitting cells to emit light in a visible light range,
wherein the first phosphor has a longer decay time than the decay time of the second phosphor,
wherein the light emitting cells are configured to be periodically turned on and off during an operation of the light emitting device,
and wherein the first phosphor is configured to emit light for a first period of time after the light emitting cells are turned off, and wherein the second phosphor is configured to emit light for a second period of time after the light emitting cells are turned off, the first period being longer than the second period.
2. The light-emitting device of claim 1 , wherein the second phosphor has a decay time less than 1 msec, wherein the decay time is a time taken to reach 10% of an initial value after the light emitted from the light emitting cells is blocked.
3. The light-emitting device of claim 2 , wherein the LED chip is configured to emit blue light, and the light emitting device is configured to emit white light through mixing the blue light with light in the visible light range emitted from the delay phosphor and light in the visible light range emitted from the second phosphor.
4. The light-emitting device of claim 3 , wherein the second phosphor is configured to emit light of yellow or green ranges.
5. The light-emitting device of claim 2 , wherein the LED chip is configured to emit ultraviolet light, and the light emitting device is configured to emit white light through mixing light in the visible light range emitted from the delay phosphor with light in the visible light range emitted from the second phosphor.
6. The light-emitting device of claim 5 , wherein the second phosphor comprises one of red, green and blue phosphors.
7. The light-emitting device of claim 1 , wherein the delay phosphor has a decay time of 1 msec or longer, wherein the decay time is a time taken to reach 10% of an initial value after the light emitted from the light emitting cells is blocked.
8. The light-emitting device of claim 1 , wherein the delay phosphor has a decay time of 8 msec or longer, wherein the decay time is a time taken to reach 10% of an initial value after the light emitted from the light emitting cells is blocked.
9. The light-emitting device of claim 1 , further comprising a bridge rectifier.
10. The light-emitting device of claim 9 , wherein the bridge rectifier comprises diodes, and the diodes comprise the light emitting cells.
11. The light-emitting device of claim 1 , wherein the light emitting cells are separate from a growth substrate.
12. The light-emitting device of claim 1 , wherein the first phosphor is configured to emit light during substantially the whole period while the light emitting cells are off, and wherein the second phosphor is configured to emit light during substantially the whole period while the light emitting cells are on and to not emit light during substantially the whole period while the light emitting cells are off.