EP1881743A2

EP1881743A2 - Lighting apparatus

Info

Publication number: EP1881743A2
Application number: EP07013491A
Authority: EP
Inventors: Shimizu Keiichi; Hashimoto Sumio; Ono Keisuke; Nishiie Mitsuhiko; Moriyama Takayoshi; Hiramatsu Takuro; Nakanishi Akiko; Toda Masahiro; Higuchi Kazunari
Original assignee: Toshiba Lighting and Technology Corp
Current assignee: Toshiba Lighting and Technology Corp
Priority date: 2006-07-10
Filing date: 2007-07-10
Publication date: 2008-01-23
Also published as: EP1881743A3; JP2013235847A; CN101106856A; CN101106856B

Abstract

A lighting apparatus is provided, which has a not lowered light output and a long life even service time is prolonged. The lighting apparatus includes a light source having a phosphor and a resin including the phosphor, and having a characteristic that as a provided electric power is increased, a decreased rate of a lumen maintenance factor is increased, and an electric-to-optical conversion efficiency is reduced; a radiation element, directly or indirectly disposed on the light source; a power source, capable of changing the electric power supplied to the light source; and a controller, reducing the electric power provided to the light source at an initial period, and making the provided electric power increase as a function of time.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a lighting apparatus such as a light emitting diode (LED).

Description of Related Art

Conventionally, a lighting apparatus as follows is provided. In order to modify the lowering of the light output because of the long time variation of a fluorescent lamp, or the lowering of the light output resulted from adhered dirt because of long time using, a service time after the replacement of the lamp is cumulatively kept, and the light is adjusted in a manner of increasing a light adjusting amount with the increase of the service time (for example referring to Reference 1, Japan Patent Publication Number HE9-97683 ).
Here, the light adjusting amount refers to a proportion of the electric power supplied to the lamp and a normal value. During the initial period of using, for example lighting is performed with a light adjusting amount of 70% of the normal value, and as the service time is increased, the light adjusting amount is increased, so as to prevent the lowering of the light output because of the long time variation of the lamp and to approximately stabilize the light output of the lamp. The control is performed to make the light adjusting amount achieve 100% (full) when the service life of the lamp is approached, the light adjusting amount is made to be relatively small when the lamp is started to be used, for example, 70% of the normal value as described above, so as to obtain an effect of saving 30% of the energy.
Even when the lamp is replaced, it is implemented according to the following manner, that is, after the lamp is replaced, the light adjusting amount is immediately set to a proportion of the light output approaching the service life versus the normal light output (for example about 70%). As the service time of the lamp goes by, the light output is increased, when the service life is approached, the light output of the lamp is made to be approximately 100%, in this manner, the light output of the lamp is stabilized for a long time (for example referring to Reference 2, Japan Patent Publication Number 2000-315589 ).
Here, the reasons of the lowering of the light output of the fluorescent lamp is as a function of time is that, the deterioration of the phosphor forming the fluorescent lamp, and the reducing of electronic radioactive substance etc. But under a situation of a light emitting element having the phosphor and a resin such as resin including the phosphor, the deterioration of the resin etc. also becomes a problem other than the phosphor.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to provide a lighting apparatus, which has a not lowered light output and a long life even service time is prolonged.
In order to realize the objective, an aspect of the present invention relates to a lighting apparatus, which includes: a light source, comprising a phosphor and a resin, and having a characteristic that as a provided electric power is increased, a decreased rate of a lumen maintenance factor is increased, and an electric-to-optical conversion efficiency is lowered; a radiation element, directly or indirectly disposed on the light source; a power source, capable of changing an electric power supplied to the light source; and a controller, reducing the provided electric power to the light source at an initial period, and increasing the provided electric power as a function of time.
According to the present invention, since the light source itself has the characteristic that as a provided electric power is increased, a decreased rate of a lumen maintenance factor is increased, and an electric-to-optical conversion efficiency is lowered, and the controller has the characteristic of reducing the provided electric power to the light source at the initial period and increasing the provided electric power as a function of time, a stabilized light output is maintained for a long time, so as to realize the long life of the light source.
Particularly, after the light source is started to be used, a relatively low provided electric power is applied from the power source according to a signal from the controller, so as to emit a predetermined relative low light output corresponding to the provided electric power from the light source. Next, as the service time of the light source goes by, the provided electric power gradually increasing according to the signal from the controller is applied to the light source. Therefore, after the light source is started to be used, the provided electric power of the power source is reduced, and further the radiation element is used to dissipate the heat of the light source, such that resins, such as the resin including phosphor and the resin reflector, will not suddenly exposed in a high temperature. Thereby the deterioration due to the heat towards the resin at the initial period can be reduced, and the lowering of the light output because of the deterioration of the resin can be restrain, and particularly the serious deterioration of the resin reflector (frame) due to heat at the initial period can be restrain
Therefore, after considering the provided electric power immediately applied after the light source is started to be used, and the lowering degree of the electrical-to-optical conversion efficiency of the light source with the increasing of the provided electric power, the proportion of the increased the provided electric power of the power source according to the signal of the controller is appropriately controlled to stabilize the light output of the light source for a long time and to realize the long life of the light source. Also, after a predetermined time, the controller maintains the provided electric power to a designed power or reduces the increased rate of the provided electric power, and reduces the deterioration of the light emitting apparatus to ease the rising curve of the provided electric power. Therefore, the deterioration of the light emitting apparatus due to the increase of the provided electric power (amount) can be reduced.
That is, as the operating temperature is lowered (raised), the electrical-to-optical conversion efficiency is increased (reduced). Therefore, in this aspect, if the operating temperature of the light source is reduced to a lower temperature, the light source itself has high light output for a long time. With the functional effect, the entire lighting apparatus can maintain the stabilized light output for a long time, and can realize the long life.
For example, when the light source comprise a light emitting diode (LED), the light source is used under a low operating temperature, so as to prevent the deterioration etc. of the resin used during installation, and particularly prevent the deterioration of the resin reflector. Also, for the light source, when an organic electro-luminescence (organic EL) element is used to replace the LED, similarly the deterioration of the used organics or resin (for example photosensitive resin) is prevented during the light source installation.
In other aspects of the present invention, the controller can generate a reference signal, for example a reference voltage, for controlling the light output of the light source. The controller reduces the reference signal (for example the reference voltage) at the initial period, and increases the reference signal (for example the reference voltage) as a function of time. In this case, the above-mentioned control is more simply performed on the light source.
Also, in another aspect of the present invention, the controller generates the reference signal according to a cumulative lighting time. In this case, the control as described above can be more simply performed on the light source.
Also, the controller further has a control signal table. In the control signal table the cumulative lighting time corresponds to a signal value. The controller outputs the reference signal corresponding to the signal value. In this case, the light source is controlled by the expected time series. When the cumulative lighting time exceeds the expected lighting time (e.g., the specified predetermined time), the controller reduces the output of the reference signal to the predetermined output, and the light output of the light source becomes a disappearing status or becomes a weak light output. Here, the weak light output is sufficiently weak to a recognizable degree to recognize, for example, the moment at the end of or just before the life time of the lighting apparatus (light source). In this case, it is reported that the lighting apparatus (light source) reaches the life time or is in a stage before reaching the life time, so the replacing period of the lighting apparatus (light source) can be known. Also, when the cumulative lighting time exceeds the expected lighting time (e.g., the final predetermined time), the controller stop the output of the reference signal and the light output of the light source. In this case, after the lighting apparatus reached the life time, the emitting is quickly terminated.
Also, the controller further has a modifying means for modifying the output fluctuation corresponding to the power source voltage. In this case, the output fluctuation resulted from the fluctuation of the power source voltage is modified, so the fluctuation of the light output is reduced. Also, the light source is a light emitting diode including a resin reflector and a light emitting element. The resin reflector has a depressed portion, and the light emitting element is disposed in the depressed portion. In this case, particularly since the serious deterioration of the resin reflector due to heat at the initial period is reduced, the lowering of the light output of the lighting apparatus with the LED can be reduced. When the decreased rate of the lumen maintenance factor reaches the predetermined value due to the deterioration of the resin reflector, for example, the decreased rate of the lumen maintenance factor is going to become ease and reach a predetermined value, the controller maintains the provided electric power to a designed power or reduces the increased rate of the provided electric power. In this case, the varying of the provided electric power as a function of the time series matches with the deterioration period of the resin reflector. That is to say, the period in which the decreased rate of the lumen maintenance factor becomes smaller due to the deterioration of the resin reflector can be accord with the period that the provided electric power maintains to a designed power or the increased rate of the provided electric power is reduced. Therefore the deterioration of the resin reflector can be reduced more effectively, and the irradiation can be performed more effectively.
In view of the above, according to the present invention, a lighting apparatus with long life is provided, wherein the light output is not deteriorated even the service time is prolonged
In order to make the aforementioned and other objects, features and advantages of the present invention comprehensible, preferred embodiments accompanied with figures are described in detail below.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
FIG. 1 is a construction view of an embodiment of a lighting apparatus according to the present invention, wherein an LED is used as a light source.
FIG. 2 is a view of an example of the whole circuit of the lighting apparatus according to the present invention.
FIG. 3 is a diagram of an example of the reference voltage generated by the controller of the lighting apparatus according to the present invention.
FIG. 4 is another example of the whole circuit of the lighting apparatus according to the present invention.
FIG. 5 is an example of the relation between the cumulative lighting time and the provided electric power.
FIG. 6 is another example of the relation between the cumulative lighting time and the provided electric power.
FIG. 7 is another example of the relation between the cumulative lighting time and the provided electric power.
FIG. 8 is another example of the relation between the cumulative lighting time and the provided electric power.
FIG. 9 is a schematic diagram of the relation of the deterioration of the resin reflector with respect to the cumulative lighting time and time series of the provided electric power.
FIG. 10 is another example of the whole circuit of the lighting apparatus according to the present invention.
FIG. 11 is a diagram of an example showing the dependence between a lumen maintenance factor and a lighting time of the light source portion of the lighting apparatus according to the present invention.
FIG. 12 is a schematic diagram showing the dependence of the light output and the lighting time of the light source portion of the lighting apparatus according to the present invention.
FIG. 13 is a schematic diagram showing the relation between the provided electric power and the electrical-to-optical conversion efficiency of the light source of the lighting apparatus according to the present invention.
FIG. 14 is a schematic diagram showing the dependence of the light output and the lighting time of the light source portion of the lighting apparatus according to the present invention.

DESCRIPTION OF EMBODIMENTS

In the following, other features and advantages of the present invention are illustrated based on the most preferred aspect for implementing the present invention. In addition, in this embodiment, a situation of using LED as the representative lighting apparatus is illustrated.
FIG. 1 is a construction view of an embodiment of a lighting apparatus according to the present invention, wherein an LED is used as the light source. An LED lamp 10 as shown in FIG. 1 has an LED chip 12 used as a light emitting element. The LED chip 12 can use, for example, blue light emitting LED chip or ultraviolet light emitting LED chip etc. The LED chip 12 is carried on a circuit pattern 15 disposed on a predetermined base member 13 with an electric insulation layer 14 positioned there-between.
The base member 13 is formed by flat plates of Al, Ni, and glass epoxy etc. with thermal diffusivity and rigidity. The circuit pattern 15 is made of alloy of Cu and Ni, and Au, etc, and is divided into an anode-side circuit pattern 15a and a cathode-side circuit pattern 15b. In the LED chip 12, a bottom surface electrode is carried and electrically connected to one of the circuit patterns 15a and 15b, for example, to the anode-side circuit pattern 15a. In the other aspect, an upper surface electrode is electrically connected to the other one of the circuit patterns 15a and 15b, for example, the cathode-side circuit pattern 15b through a bonding wire 16.
A frame 18 is disposed on the substrate 13, and forms a depressed portion 17 of a cone-trapezoid shape facing upward and having a gradually increased diameter. The LED chip 12 is disposed in the depressed portion 17. The depressed portion 17 is formed as the cone-trapezoid shape having, for example, a bottom surface diameter of 2.0-4.0 mm, an upper surface diameter of 1.5-4.5 mm, and a depth of 0.5-1.0 mm. The frame 18 is made of, for example, polybutylene terephthalate (PBT), polyphthalamide (PPA), and Polycarbonate (PC) etc.
In the depressed portion 17 with the LED chip 12 disposed, a phosphor-containing resin layer 19 made of transparent heat-hardening resin containing phosphor is disposed. The LED chip 12 is sealed in the depressed portion 17 by using the phosphor-containing resin layer 19. An injection apparatus such as a dispenser is used to inject the transparent liquid heat-hardening region mixed with the phosphor in the depressed portion 17 with the LED chip 12 disposed, and heat hardening is performed by using the following method, so as to form the phosphor-containing resin layer 19.
In addition, in the drawing, an upper end face of the phosphor-containing resin layer 19 and an upper end of the depressed portion 17 are made to be on the same horizontal plane, but it is not particularly limited here.
The phosphor-containing resin layer 19 seals the LED chip 12 in the depressed portion 17, and serves as the light emitting portion. That is, the phosphor contained in the phosphor-containing resin layer 19 is excited by the light emitted from the LED chip 12, such as blue light or ultraviolet, so as to emit visible light.
The transparent liquid heat-hardening resin used to form the phosphor-containing resin layer 19 includes silicone rubber, silicone resin, and epoxy resin etc. The phosphor contained in the heat-hardening resin as described above is not particularly limited, and is appropriately selected according to the objective such as a light emitting color of the LED lamp 10.
For example, when the blue light emitting LED chip 12 is used to obtain a white light emitting, mainly a yellow color system phosphor emitting the light between yellow light and orange light is used. In order to improve the color rendering properties and etc., red light emitting phosphor can also be used besides the yellow color system phosphor. For the yellow color system phosphor emitting the light between yellow light and orange light, for example, Yttrium Aluminum Garnet (YAG) phosphor such as RE₃(Al,Ga)₅O₁₂:Ce phosphor (RE represents at least one selected from Y, Gd, and La, and the same as follows), and silicate phosphor such as AE₂SiO₄:Eu phosphor (AE is alkaline earth elements such as Sr, Ba, or Ca) can be used.
When the ultraviolet light emitting LED chip 12 is used to obtain the white light emitting, mainly a red, green, blue (RGB) phosphor is used. For the blue light emitting phosphor, halophosphate phosphor such as AE₁₀(PO₄)₆Cl₁₂:Eu phosphor, or aluminate phosphor such as (Ba,Mg)Al₁₀O₁₇:Eu phosphor, can be used. For the green light emitting phosphor, aluminate phosphor such as (Ba,Mg)Al₁₀O₁₇:Eu,Mn phosphor can be used. For the red light emitting phosphor, oxysulfide phosphor such as La₂O₂S:Eu phosphor can be used.
Further, the phosphor can also be replaced, according to the composition, nitride system phosphor (e.g. E₂Si₅N₈:Eu), nitrogen oxide system phosphor (e.g. Y₂Si₃O₃N₄:Ce), sialon system phosphor (e.g. AEx(Si,Al)₁₂(N,O)₁₆:Eu) and etc. capable of obtaining various light emitting colors can be applied. In addition, the LED lamp 10 is not limited to the white light emitting lamp, and can also be constructed to have the light emitting color besides white. When the LED lamp 1 is used to obtain the light emitting color besides white, for example the intermediate color light emitting, various phosphor can be appropriately used according to the objective light emitting color.
The phosphor can be any one of dispersion type and sedimentation type phosphor.
Next, FIG. 2 shows an example of the whole circuit construction of the lighting apparatus according to the present invention including the LED lamp 10 as shown in FIG 1.
As shown in FIG. 2, the lighting apparatus of the present invention has the LED lamp 10, a power source 20, and a controller 30.
The power source 20 has a rectifier DB, such as a diode bridge performing a full wave rectification on an alternating current (AC) power source 21, such as a commercial power source, and uses a direct current obtained after using a smoothing condenser C1 to smooth an output voltage of the rectifier DB as the power source. A transistor T1 is connected to an end side of the smoothing condenser C1. The transistor T1 is controlled by a driving circuit 22. Further, the power source 20 includes a series circuit formed by a diode D1, an inductor L1 and a condenser C2, and forms a buck chopper circuit.
The driving circuit 22 turns the transistor T1 on or off. When the transistor T1 is turned on, energy is stored in the condenser C2 through the inductor L1. When the transistor T1 is turned off, the energy stored in the condenser C2 is supplied to the light source portion 10. In this manner, the electric power is supplied to the light source portion 10, so as to maintain the lighting.
In addition, a current-voltage converting circuit 23 is disposed in the power source 20. After the electric power (current) supplied to the light source portion 10 is converted to the voltage, it is guided to an error amplifying circuit of the controller as shown as follows.
The controller 30 has a cumulative lighting time keeping circuit 31 and a functional circuit 32. The cumulative lighting time keeping circuit 31 counts the totalized lighting time (cumulative lighting time) beginning from the lighting of the light source portion 10. The functional circuit 32 forms a corresponding predetermined reference voltage Vs from the counted cumulative lighting time, and supplies the predetermined reference voltage Vs to the error amplifying circuit 33.
The reference voltage Vs is supplied by the time series as shown in Fig. 3. That is, at the initial period of the beginning of the lighting of the light source portion 10, the reference voltage Vs is supplied with a relatively low value, and the value is raised as the cumulative lighting time increases.
In the error amplifying circuit 33, a voltage value from the power source 20 is compared with the reference voltage Vs from the controller 30, so as to make the voltage value from the power source 20 be the same as the reference voltage Vs from the controller 30, and to transmit a predetermined signal to the driving circuit 22 of the power source 20. According to the signal, the driving circuit 22 turns the transistor T1 on or off, and makes the voltage value supplied to the light source portion 10 be substantially the same as the reference voltage Vs. In this manner, a voltage (electric power) corresponding to the reference voltage Vs is supplied to the light source portion 10, so as to perform the lighting operation with the voltage (electric power) based on the reference voltage Vs.
In the above example of the circuit construction, the reference voltage Vs supplied to the error amplifying circuit 33 as a function of time series is as shown in FIG 3. That is, a relatively low provided electric power the same as the relatively low reference voltage Vs from the controller 30 is applied from the power source 20 immediately after the light source portion 10 is started to be used (lighting). In this manner, the light source portion 10 emits a predetermined relatively low light output corresponding to the provided electric power. Next, as the using (lighting) time of the light source portion 10 goes by, the reference voltage Vs of the controller 30 is increased. Therefore, the power source 20 applies the gradually increased provided electric power to the light source portion 10. Therefore, in this case, the light output is modified by, for example, a controller recorded in the Reference 2, Japan Patent Publication Number 2000-315589 .
Further, in the above example of the circuit construction, after the light source portion 10 such as the LED lamp as shown in FIG. 1 is started to be used, a relatively low provided electric power is applied from the power source 20 according to a signal from the controller 30. In this manner, the light source portion 10 emits a predetermined relatively low light output corresponding to the provided electric power. Next, as the service time of the light source goes by, a gradually increased provided electric power is applied to the light source according to the signal from the controller.
In this manner, after the light source portion 10 is started to be used, the provided electric power from the power source 20 is reduced, and the heat of the light source portion 10 is dissipated by a radiation element. Therefore, the sudden exposure of the resin, such as the resin reflector 18 and a resin layer 19 including the phosphor, under the high temperature can be reduced, and the deterioration of the resin due to heat at the initial period can also be reduced, and particularly the serious deterioration of the resin reflector 18 due to heat at the initial period can be reduced. Therefore, the lowering of the light output due to the deterioration of the resin can be reduced.
Therefore, considering the provided electric power applied after the light source portion 10 is started to be used, and the lowering degree of the electrical-to-optical conversion efficiency of the light source with the increase of the provided electric power, the proportion of the increased provided electric power of the power source 10 according to the signal of the controller 30 is appropriately controlled, thereby stabilizing the light output of the light source 10 for a long time and realizing the long life of the light source.
That is, as the operating temperature is lowered (raised), the electrical-to-optical conversion efficiency is increased (reduced). Therefore, if the operating temperature of the light source portion 10 is reduced to a relative low temperature, the light source itself has high light output for a long time. With the functional effect, the entire lighting apparatus can maintain the stabilized light output for a long time, and can realize the long life.
Next, FIG. 4 is another example of the whole circuit of the lighting apparatus according to the present invention. Also, repeated description of the items described in the above example of the circuit construction is omitted. As shown in FIG 4, being difference from the conventional example of the circuit construction, the example of the circuit construction does not have the current-voltage converting circuit 23 and the error amplifying circuit 33, and performs an open loop control instead of a feedback control. The controller 30 can adopt the relation of the provided electric power (W) and the cumulative lighting time (H) as a function of time series in various forms. For example, the controller 30 can uses the functional circuit 32 to convert the cumulative lighting time calculated by the cumulative lighting time keeping circuit 31 to the signal (reference signal) S corresponding to the cumulative lighting time, and the reference signal S is supplied to a driving circuit 22a of the power source 20. In the driving circuit 22a, the transistor T1 is turned on or off according to the reference signal S, thereby specifying the voltage (electric power) to be supplied into the light source portion 10, i.e., the provided electric power.
Also, in the example of the circuit construction, the controller 30 has a control signal table making the cumulative lighting times correspond with the signal values as a function of time series. For example, the control signal table is pre-stored in a memory portion (not shown) of the functional circuit 32, and the cumulative lighting time keeping circuit 31 is used to count the cumulative lighting time. A calculation portion (not shown) of the functional circuit 32 extracts the reference signal S corresponding to the cumulative lighting time from the control signal table of the memory portion. A signal output portion (not shown) of the functional circuit 32 supplies the reference signal S to the driving circuit 22a. In the driving circuit 22a, the transistor T1 is turned on or off corresponding to the reference signal S, thereby specifying the voltage (electric power) to be supplied into the light source portion 10, i.e., the provided electric power. Also, when the cumulative lighting time reaches a plurality of preset specified times, the changeable predetermined reference signal S is supplied to the driving circuit 22a according to the control signal table.
The relation of the cumulative lighting time and the provided electric power as a function of time series is shown as follows. In FIG. 5, the provided electric power is increased in a certain proportion as the cumulative lighting time goes by, after the expected cumulative lighting time is reached, the provided electric power is maintained to a designed power. In the example of FIG. 6, as the cumulative lighting time goes by, the provided electric power is increased in stages (stage by stage) with a predetermined interval, after the expected cumulative lighting time is reached, the provided electric power is maintained to a designed power. In the example of FIG. 7, for example in the relation of the cumulative lighting time and the provided electric power of FIG. 6, when the predetermined cumulative lighting time (predetermined specified time) is reached, the provided electric power nearly becomes zero. In the example of FIG. 8, for example in the relation of the cumulative lighting time and the provided electric power, when the predetermined cumulative lighting time (final specified time) is reached, the provided electric power is zero. Therefore, by specifying the relation of the cumulative lighting time and the provided electric power, under the condition of FIG. 5, after the predetermined cumulative lighting time is reached, the provided electric power is maintained to a designed power, so the early deterioration of the light emitting apparatus due to the increase of the provided electric power (amount) can be reduced. Under the condition of FIG. 6, the provided electric power is increased in stages, so the light output can be maintained constant in a certain period. Also, under the condition of FIG. 7, the replacing period of the light source portion (LED lamp) can be known. Under the condition of FIG. 8, the light emitting of the light source portion (LED lamp) reaching the life is stopped. Also, the form of the increasing of the provided electric power relative to the cumulative lighting time is not limited to the forms of FIGs. 5 and 6. Also, when the predetermined accumulative lighting time in FIGs. 7 and 8 is reached, the form of reducing the provided electric power (till nearly zero) or stopping is not limited to the form of FIG 6, and the form of FIG 5 is also available.
Next, the relation of the deterioration of the resin reflector 18 and the provided electric power by the time series is illustrated. FIG 9 is a schematic diagram of the relation of the deterioration of the resin reflector with respect to the cumulative lighting time and time series of the provided electric power. Dashed line indicates the relation of the cumulative lighting time of the resin reflector 18 and the decreased rate of the lumen maintenance factor of the lighting apparatus 1. Real line indicates the relation of the cumulative lighting time and the provided electric power. As shown by the dashed line of FIG 9, the resin reflector 18 is quickly deteriorated due to heat at the initial period, and the lumen maintenance factor is greatly reduced. It is discovered by the present inventors that the decreased rate of the lumen maintenance factor eases (small) as a function of time, and in the predetermined cumulative lighting time, the lumen maintenance factor is approximately converged to a constant value (i.e., the decreased rate approaches zero). Therefore, for example, a construction can be formed, in the construction, when the decreased rate of the lumen maintenance factor becomes ease and reaches the predetermined value (i.e., predetermined threshold value, e.g., Taof FIG. 10) due to the deterioration of the resin reflector 18, the provided electric power can be maintained to a designed power or the increased rate of the provided electric power is reduced. According to the above construction, the varying of the provided electric power as a function of time series is made to accord with the deterioration period of the resin reflector 18. That is to say, the characteristic of the resin reflector can be pre-mastered, so as to easily control the light output to be constant. Also, the predetermined value (predetermined threshold value) can be properly determined, for example according to the decreased rate of the lumen maintenance factor varying with time due to the deterioration of the resin reflector 18, and according to the life time of the lighting apparatus etc..
Next, FIG. 10 is another example of the whole circuit of the lighting apparatus according to the present invention. Also, the repeated description of the described items in the above example of the construction of the circuit is omitted. As shown in FIG 10, the controller 30 of the lighting apparatus has a power source fluctuation modifying (compensating) circuit 34 for modifying the fluctuation of the power source current. The power source fluctuation modifying (compensating) circuit 34 is parallel with an AC power source AC21, and is disposed in series with the driving circuit 22a. When the power source voltage of the AC power source AC21 is altered, the reference signal S flowing towards the driving circuit 22a is changeable, so as to modify (compensate) the fluctuation of the power source voltage. Particularly, for example, the power voltage when the power source is not altered (before compensation) is represented by V₀, the reference signal is represented by So. When the power source voltage becomes V₁ because of the fluctuation of the power source, by a reference signal S₁ (the reference signal So is modified to be the reference signal S₁) satisfying, for example, the following equation $V$ $_{0} / V_{1} = k * S_{1} / S_{0}$

(in the equation, k is a specified coefficient),
the power source fluctuation modifying (compensating) circuit 34 can modify (compensate) the fluctuation of the power source voltage. Therefore, the power source fluctuation modifying (compensating) circuit 34 can be used to modify the fluctuation of the power source current, so as to make the light output become a constant value.
FIG. 11 is a diagram of an embodiment showing the dependence between a lumen maintenance factor and a lighting time of the light source portion 10. In this embodiment, for example the light source having the lighting time dependence (reducing) of the lumen maintenance factor as shown in FIG. 11 can be used. It is known from FIG 11 that in the full time, as the electric power (current) supplied to the light source is larger, the lumen maintenance factor is reduced (particularly, in FIG. 11, in the same lighting time, the current value is increased to 20 mA to 60 mA, so the lumen maintenance factor is reduced). That is to say, as the provided electric power (current) is increased (for example, the current value is increased from 20 mA to 60 mA), the decreased rate of the lumen maintenance factor is increased.
In addition, it is known that in this embodiment, as the electric power (current) supplied to the light source is increased, the heat is increased, and the ambient temperature is raised. Therefore, as shown in FIG.11, the light source having the following characteristic is preferably used, i.e., the light source with the electrical-to-optical conversion efficiency lowered as the operating temperature is raised. When the light source is the LED lamp with the construction as shown in FIG. 1, the deterioration of the resin used in the LED lamp, such as the resin layer 19 containing the phosphor and the resin reflector (frame) 18, and especially the resin reflector 18 due to heat generated by long time using of the light source, can be reduced. For example, due to the deterioration the resin reflector 18 yellows and the reflecting surface thereof is deteriorated particularly in the initial period. Therefore, the reflecting rate is lowered, and the light extraction efficiency is lowered as well. Therefore, the reflecting surface of the resin reflector 18 is particularly deteriorated in the initial period. Because of the effect of the difference of a heat conductivity of the resin reflector 18 and a heat conductivity of the resin layer 19 containing the phosphor, it is presumed that the reflecting surface is more easily affected by the heat.
FIG. 12 is a schematic diagram showing the dependence of the light output and the lighting time of the light source according to the phenomenon mentioned above. It is known from FIG. 11 that if as the lighting time goes by, the light source is set to reach the life when, for example, the light beam (light output) is reduced to 70% at the initial period, the conventional light source reaches the life at the time T1. However in this embodiment, at the initial period of the lighting, the light beam (light output) of the light source is preset to, for example, 70%. Therefore, the life of the light source is prolonged to T2.
FIG. 13 is a schematic diagram showing the relation between the provided electric power and the electrical-to-optical conversion efficiency of the light source. In FIG. 13, the real line indicates the condition when the operating temperature is low, and the dashed line indicates the condition when the operating temperature is high. It is known from FIG. 13 that as the provided electric power is increased (reduced), the electrical-to-optical conversion efficiency is reduced (increased), but the lower the operating temperature is, the higher the conversion efficiency is. Therefore, as shown in FIG 14, if the operating temperature of the light source is reduced to a relatively low temperature, the light source itself has high light output for a long time. With the functional effect, the life of the light source is prolonged to T3 longer than T2.
The present invention is illustrated in detail according to the specific embodiment in the above, but the present invention is not limited to the specific embodiment without departing from the scope of the present invention, and various derivations or alternations can be performed.
For example, in the specific embodiment, LED is mainly used as the light source for the illustration. Definitely, light sources other than the LED can also be used, for example, the organic EL.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.

Claims

A lighting apparatus (1), comprising:
a light source (10), including a phosphor and a resin (19), and having a characteristic that as a provided electric power is increased, a decreased rate of a lumen maintenance factor is increased, and an electric-to-optical conversion efficiency is lowered;

a radiation element, directly or indirectly disposed on the light source (10);

a power source (20), capable of supplying a variable electric power to the light source (10); and

a controller (30), reducing the provided electric power to the light source (10) at an initial period, and increasing the provided electric power as a function of time.
The lighting apparatus (1) according to claim 1, wherein the controller controls the provided electric power to stabilize a light output of the light source (10).
The lighting apparatus (1) according to claim 1, wherein the controller (30) maintains the provided electric power to a designed power or reduces an increased rate of the provided electric power as a function of time.
The lighting apparatus (1) according to any one of claims 1 to 3, wherein the light source (10) has a characteristic that as an operating temperature of the light source (10) is raised, the electrical-to-optical conversion efficiency is lowered.
The lighting apparatus (1) according to any one of claims 1 to 4, wherein the controller (30) generates a reference signal (S) for controlling a light output of the light source (10) and reduces the reference signal (S) at the initial period, and increases the reference signal (S) as a function of time.
The lighting apparatus according to any one of claims 1 to 5, wherein the controller generates a reference signal for controlling a light output of the light source according to a cumulative lighting time.
The lighting apparatus (1) according to any one of claims 1 to 6, wherein the controller (30) further comprises a control signal table in which a cumulative lighting time corresponds to a signal value, so as to output a reference signal (S) for controlling a light output of the light source (10), and the reference signals (S) corresponds to the signal value.
The lighting apparatus (1) according to any one of claims 1 to 7, wherein the controller (30) further comprises a modifying means for modifying an output fluctuation corresponding to a power source voltage.
The lighting apparatus (1) according to any one of claims 1 to 8, wherein the light source (10) is a light emitting diode comprising a resin reflector (18) and a light emitting element (12), wherein the resin reflector (18) has a depressed portion (17), and the light emitting element (12) is disposed in the depressed portion (17).
The lighting apparatus (1) according to claim 9, wherein the controller (30) maintains the provided electric power to a designed power or reduces an increased rate of the provided electric power when a decreased rate of the lumen maintenance factor reaches a predetermined value due to a deterioration of the resin reflector (18).