Timepiece with light emitting device

A timepiece comprises a display including a light emitting element. A detector detects ambient light around the timepiece and a switch is switchable into first and second operating modes. When the switch is in the first mode the light emitting element is illuminated at a first brightness level when the detected ambient light is below a predetermined level and the light emitting element is not illuminated when the detected ambient light is above the predetermined level. When the switch is in the second mode, the light emitting element is illuminated at a second brightness level which is greater than the first brightness level.

BACKGROUND OF THE INVENTION 
1. [Field of Industrial Application] 
The present invention relates to a timepiece with a light emitting device, 
in which a light emitting element is mounted on the display portion (e.g., 
hands, letters or clockface) of the timepiece. 
2. [Prior Art] 
There exists in the prior art a timepiece with a light emitting device, in 
which a light emitting element such as an EL (Electro Luminescence) 
element is mounted on the display portion (e.g., hands, letters or 
clockface) of the timepiece so that it may be easily observed even when 
the surroundings are dark as in the nighttime. 
In this timepiece with the light emitting device, the brightness of the 
light emitting element is as low as possible so that the power consumption 
may be minimized. 
3. [Problems to Be Solved] 
In the aforementioned timepiece with the light emitting device of the prior 
art, the illumination of the light emitting element cannot be sufficiently 
recognized even if it is demonstrated when the surroundings are bright as 
in the daytime. If the brightness of the light emitting element is so 
increased that it can be sufficiently recognized even in the daytime, the 
power consumption is accordingly increased to raise a disadvantage that 
the battery runs out within a short time. 
SUMMARY OF THE INVENTION 
The present invention has been conceived so as to solve the above-specified 
problems of the prior art and has an object to provide a timepiece with a 
light emitting device, in which the illumination of the light emitting 
element can be sufficiently recognized even when the surroundings are 
bright.

[EMBODIMENTS] 
The present invention will be described in the following in connection with 
its embodiments with reference to the accompanying drawings. 
EMBODIMENT 1 
FIG. 1 shows a first embodiment of the present invention. 
In FIG. 1, reference numeral 1 designates a light emitting element which is 
disposed on the display portions of a timepiece such as the hands of the 
timepiece, the letters or numerals indicating the time, or the face of the 
timepiece and which is composed of EL elements EL1, EL2 and EL3. Numeral 2 
designates light detecting means for detecting the brightness around the 
timepiece. This light detecting means is composed of a photoconductive 
cell such as CdS (i.e., cadmium sulfur). Numeral 3 designates switching 
means for switching a first mode, in which the light emitting element 1 is 
caused to illuminate with a predetermined brightness when in the darkness 
where the brightness of the light detected by the light detecting means 2 
is lower than a predetermined brightness and not to illuminate when in the 
brightness where the detected brightness is higher than a predetermined 
brightness, and a second mode in which the light emitting element 1 is 
caused to illuminate more brightly than the illumination in the darkness 
of the first mode. 
The EL elements used in the light emitting element 1 have to be driven with 
an AC voltage of several tens of volts or more so that they may be caused 
to illuminate. In the present embodiment, resistors R1 and R2, capacitors 
C1, C2, Ca and Cp, a transformer TR, a transistor T1 and the EL elements 
EL1, EL2 and EL3 constitute altogether a blocking oscillator for driving 
the EL elements used in the light emitting element 1 with the AC voltage. 
Usually, the DC voltage (of about 3 V) of a DC power source DC using a 
battery is converted into an AC voltage (of an effective value of 40 to 80 
V) having a frequency of several hundred Hz, which is applied to the EL 
elements. 
The capacitor Ca connected between the transformer TR and the EL elements 
EL1, EL2 and EL3 is effective for the blocking oscillator to oscillate 
stably even if a leakage is caused between the two electrodes of the EL 
elements EL1, EL2 and EL3. The capacitance of the capacitor Ca is 
preferably five or more times as large as the parallel capacitance of the 
EL elements EL1, EL2 and EL3. Despite this fact, however, the capacitor Ca 
may be omitted if there is no fear of leakage between the two electrodes 
of the EL elements EL1, EL2 and EL3. 
The capacitor Cp connected in parallel with the EL elements EL1, EL2 and 
EL3 is used to drop the frequency for the alternate drive to thereby 
elongate the lifetimes of the EL elements EL1, EL2 and EL3 (It is 
generally said that the lifetimes of the EL elements are inversely 
proportional to the drive frequency). 
In the transformer TR, the connection a - c or b -c constitutes a primary 
side, a connection c - d constitutes a secondary side, and a connection e 
- f constitutes a ternary side. 
Next, the switching of the switching means 3 and the light emitting states 
of the light emitting element 1 accompanying the changes in the amount of 
the light detected by the light detecting means 2 will be described in the 
following. (A) In the operation when the switching means 3 is set in the 
first mode (i.e., when the switch is set at AT1): 
When the switching means 3 is set in the first (auto-) mode in which the 
light emitting state of the light emitting element 1 is automatically set 
in accordance with the brightness around the timepiece, the following 
operations are accomplished in accordance with the brightness of the light 
detected by the light emitting element 2. 
First of all, the following operations are accomplished when the brightness 
of the light detected by the light detecting means 2 is lower than a 
predetermined brightness (of several luxes in the present embodiment). 
The photoconductive cell used as the light detecting means 2 has its 
resistance raised to a high value to turn on a transistor T2 so that a 
transistor T3 is accordingly turned on. As a result, the transformer TR 
has its connection a - c constituting the primary side to apply the 
predetermined AC voltage (e.g., 50 V) to the EL elements EL1, EL2 and EL3 
so that the light emitting element 1 illuminates with a low luminance. 
Next, the following operations are accomplished when the brightness of the 
light detected by the light detecting means 2 is higher than a 
predetermined brightness. 
The photoconductive cell used as the light detecting means 2 has its 
resistance dropped to a low level to turn off the transistor Tr2 so that 
the transistor T3 is also turned off. As a result, no current flows to the 
primary side of the transformer TR to apply no AC voltage to the EL 
elements EL1, EL2 and EL3 so that the light emitting element 1 does not 
illuminate. (B) In the operation when the switching means 3 is set in the 
second mode (i.e., when the switch is set at DM1): 
When the switching means 3 is set in the second mode (i.e., the 
demonstration mode) in which the light emitting element 1 is caused to 
illuminate with a high luminance, the following operations are 
accomplished. 
The transformer TR has its connection b - c constituting the primary side. 
Since the number of turns of the primary side is smaller than that of the 
foregoing operation (A), the EL elements EL1, EL2 and EL3 are fed with a 
higher AC voltage (e.g., 75 V) than that of the operation (A) so that the 
light emitting element 1 illuminates with a high luminance. In the present 
embodiment, as is apparent form FIG. 1, the light emitting element 1 
illuminates with the high luminance independently of the brightness of the 
light detected by the light detecting means 2. 
Since, in this mode, the light emitting element 1 illuminates highly 
brightly even if the surroundings are bright as in the daytime, the 
illumination of the light emitting element 1 can be recognized without 
fail. This highly bright emission is effective especially when the light 
emitting element 1 is caused to demonstrate in the bright surroundings. 
Here, generally speaking, it is known in the art that the emission 
luminance of an EL element is proportional to the frequency of the AC 
drive. Thus, when the switching means 3 is set in the first (auto-) mode 
described in the foregoing item (A), the connection x -y of FIG. 1 is 
electrically shorted to connect the capacitor Cp in parallel with the EL 
elements EL1, EL2 and EL3 so that these elements EL1, EL2 and EL3 may be 
alternatively driven with a low frequency. When, on the other hand, the 
switching means 3 is set in the second mode (i.e., the demonstration mode) 
described in the foregoing item (B), the connection x - y of FIG. 1 is 
electrically opened to disconnect the capacitor Cp so that the EL elements 
EL1, EL2 and EL3 are driven with the AC voltage of high frequency. In 
these ways, too, it is possible to control the low- and high-luminance 
illuminations by the EL elements EL1, EL2 and EL3. At this time, it is not 
always necessary to increase or decrease the number of turns of the 
primary side for each mode. 
In the present embodiment, the modes may be suitably switched, as follows. 
The switching means is usually set at the first (auto-) mode so that the 
light emitting elements may automatically illuminate with the low 
luminance when the surroundings are dark (or in the darkness). When the 
surroundings are bright (or in the brightness), the switching means is 
desirably set at the second mode (i.e., the demonstration mode) so that 
the light emitting elements may illuminate with the high luminance. As a 
result, in the normal state, the light emitting elements can illuminate 
automatically with the low luminance only in the darkness to reduce the 
power consumption. If necessary, moreover, another setting can be so made 
that the light emitting elements may illuminate with the high luminance. 
Thus, the socalled "demonstration function" can be performed with an 
excellent visibility even when the surroundings are bright. 
EMBODIMENT 2 
FIG. 2 shows another embodiment of the present invention. 
In FIG. 2, the numerals and symbols identical to those of FIG. 1 have the 
same functions as those of the foregoing embodiment excepting those as 
will be described in the following. Therefore, these are fundamentally 
similar to those of the first embodiment so that their descriptions will 
be omitted. 
The switching of the switching means 3 and the light emitting states of the 
light emitting element 1 accompanying the changes in the amount of the 
light detected by the light detecting means 2 will be described in the 
following. 
(C) In the operation when the switching means 3 is set in the first mode 
(i.e., when the switch is set at AT2): 
The functions and operations at this time are similar to those of the 
aforementioned case (A) of the first embodiment, and their descriptions 
will be omitted. 
(D) In the operation when the switching means 3 is set in the third mode 
(i.e., when the switch is set at DM2): 
The following operations are accomplished when the switching means 3 is set 
in the third mode (i.e., the demonstration mode) in which the light 
emitting element 1 is caused to illuminate with a high or low brightness. 
First of all, the following operations are accomplished when the brightness 
of the light detected by the light detecting means 2 is higher than a 
predetermined brightness (e.g., several luxes in the present embodiment). 
Since the photoconductive cell used as the light detecting means 2 has its 
resistance reduced to a low level, the transistor T2 is turned off so that 
the transistor T3 is also turned off. Since, moreover, a transistor T4 is 
also off, a transistor T5 is turned on by the actions of resistors R8 and 
R9. As a result, the transformer TR has its b - c connection constituting 
the primary side, the number of turns of the primary side is smaller than 
that of the mode (C) so that the EL elements EL1, EL2 and EL3 are fed with 
a higher AC voltage (e.g., 75 V) than that of the foregoing mode (C) to 
cause the light emitting element 1 to illuminate with a high luminance. 
Next, the following operations are accomplished in the darkness when the 
brightness of the light detected by the light detecting means 2 is lower 
than a predetermined brightness. 
The photoconductive cell used as the light emitting means 2 has its 
resistance raised to a high level to turn on the transistor T2 so that the 
transistor T3 is turned on. As a result, the transistor TR has its a- c 
connection constituting the primary side to apply a predetermined AC 
voltage (e.g., 50 V) to the El elements EL1, EL2 and EL3 so that the light 
emitting element 1 illuminates with a low luminance. 
Since, in this mode, the light emitting element 1 illuminates highly 
brightly even if the surroundings are bright as in the daytime, the 
illumination of the light emitting element 1 can be recognized without 
fail. This highly bright emission is effective especially when the light 
emitting element 1 is caused to demonstrate in the bright surroundings. 
When, on the contrary, the surroundings are dark as in the night, the 
illumination of the light emitting element 1 can also be recognized 
without fail even if its luminance is low. Thus, the power consumption can 
be reduced by causing the light emitting element 1 to illuminate with a 
low luminance. 
(E) In the operation when the switching means 3 is normally set in the 
illuminating mode (i.e., when the switch is set at ON): 
In this mode, the light emitting element 1 is always caused to illuminate 
with a low luminance independently of the brightness of the light detected 
by the light detecting means 2. 
In the present mode, as is apparent from FIG. 2, the transformer TR has its 
connection a - c constituting the primary side independently of the 
brightness of the light detected by the light detecting means 2. As a 
result, the predetermined AC voltage (e.g., 50 V) is applied to the EL 
elements EL1, EL2 and EL3 so that the light emitting element 1 illuminates 
with a low luminance. 
(F) In the operation when the switching means 3 is normally set in the 
non-illuminating mode (i.e., when the switch is set at OFF): 
In the present mode, as is apparent from FIG. 2, no current flows to the 
primary side of the transformer TR to apply no AC voltage to the EL 
elements EL1, EL2 and EL3 so that the light emitting element 1 does not 
illuminate at all times. 
In the present embodiment, it is not necessary to set the aforementioned 
(E) (the normally illuminating mode) of (F) (the normally non-illuminating 
mode). 
In the present embodiment, the switching means may normally be set at the 
first (auto-) mode so that the light emitting element may illuminate with 
the low luminance when the surroundings become dark (in the darkness). 
When the surrounding are bright (in the brightness), the switching means 
may be set, if necessary, to the third mode (i.e., the demonstration mode) 
to cause the light emitting element to illuminate with the high luminance. 
As a result, in the normal state, the light emitting elements can 
illuminate automatically with the low luminance only in the darkness to 
reduce the power consumption. If necessary, moreover, another setting can 
be so made that the light emitting elements may illuminate with the high 
luminance. Thus, the so-called "demonstration function" can be performed 
with an excellent visibility even when the surroundings are bright. In 
case, on the other hand, the switching means is set to the third mode 
(i.e., the demonstration mode) when the surroundings are dark as in the 
night, the light emitting element illuminates with the low luminance so 
that the power consumption can be reduced to a lower value than that of 
the foregoing first embodiment (in which the light emitting element always 
illuminates with the high luminance in the demonstration mode 
independently of the brightness of the surroundings). 
Incidentally, the switching means can be set to the "normally 
non-illuminating mode" in the bedtime of night and to the third mode, when 
the time is to be confirmed in the bedtime, so that the light emitting 
element may illuminate with the low luminance. 
EMBODIMENT 3 
FIG. 3 shows a third embodiment of the present invention. 
In FIG. 3, the numerals and symbols identical to those of FIG. 1 have the 
same functions as those of the first embodiment excepting those as will be 
described in the following. Therefore, these are fundamentally similar to 
those of the first embodiment so that their descriptions will be omitted. 
The switching of the switching means 3 and the light emitting states of the 
light emitting element 1 accompanying the changes in the amount of the 
light detected by the light detecting means 2 will be described in the 
following. 
(G) In the operation when the switching means 3 is set in the fourth mode 
(i.e., when the switch is set at AT3): 
When the switching means 3 is set in the first (auto-) mode in which the 
light emitting state of the light emitting element 1 is automatically set 
in accordance with the brightness around the timepiece, the following 
operations are accomplished in accordance with the brightness of the light 
detected by the light emitting element 2. 
First of all, the following operations are accomplished when the brightness 
of the light detected by the light detecting means 2 is lower than a 
predetermined brightness (of several luxes in the present embodiment). 
In accordance with the brightness of the light detected by light detecting 
means 2', the resistance of photosensitive cell is changed such that it 
takes the larger value for the lower brightness. In accordance with the 
magnitude of the resistance, the bias voltage of a transistor T6 is 
changed. As is apparent from FIG. 3, the transformer TR has its connection 
a - c constituting the primary side which has its current changing with 
the conductivity of the transistor T6. Specifically, the current flowing 
through the transformer TR is reduced to the lower rate as the brightness 
of the light detected by the light detecting means 2 is the lower, so that 
the AC voltage to be applied to the EL elements EL1, EL2 and EL3 is 
reduced to drop the brightness of the light emitting element 1. 
Since, in this present mode, the light emitting element 1 is set to 
illuminate with the lower luminance in the darker surroundings of the 
timepiece, it can be caused to illuminate with the optimum brightness for 
the brightness of the surroundings so that the display of the timepiece 
can become obvious. 
Next, the following operations are accomplished in the brightness where the 
brightness of the light detected by the light detecting means 2 is higher 
than a predetermined brightness. 
The photoconductive cell used as the light detecting means 2 has its 
resistance dropped to a lower value to turn off the transistor T2 so that 
the transistor T6 is also turned off. As a result, no current flows to the 
primary side of the transformer TR, and the no AC voltage is applied to 
the EL elements EL1, EL2 and EL3 so that the light emitting element 1 does 
not illuminate. 
(H) In the operation when the switching means 3 is set in the fifth mode 
(i.e., when the switch is set at DM3): 
The following operations are accomplished when the switching means 3 is set 
in the second mode (i.e., the demonstration mode) where the light emitting 
element 1 is caused to illuminate with a high luminance. 
The transformer TR has its connection b - c constituting the primary side. 
Since the number of turns of the primary side resultantly becomes less 
than that of the aforementioned mode (G), the EL elements EL1, EL2 and EL3 
are fed with a higher AC voltage (e.g., 75 V) than the highest AC voltage 
(e.g., 50 V) supplied in the mode (G) so that the light emitting element 1 
illuminates with the high luminance. In the present embodiment, as is 
apparent from FIG. 3, the light emitting element 1 illuminates with the 
high luminance independently of the brightness of the light detected by 
the light detecting means 2. 
In the present mode, the light emitting element 1 illuminates with the high 
luminance even when the surroundings are bright as in the daytime, so that 
the illumination of the light emitting element 1 can be recognized without 
fail. This illumination is effective especially if the light emitting 
element 1 is caused to demonstrate when the surroundings are bright. 
In the present embodiment, the switching means is normally set in the 
fourth (auto-) mode only in the darkness, so that the light emitting 
element may illuminate within a low-luminance region in accordance with 
the brightness of the surroundings, and in the fifth mode (i.e., the 
demonstration mode), if necessary, when the surroundings are bright (in 
the brightness), so that the light emitting element may illuminate with 
the high luminance. As a result, the light emitting element can be 
normally caused to illuminate in the lowluminance region only in the 
darkness in accordance with the brightness of the surroundings to reduce 
the power consumption. If necessary, moreover, the light emitting element 
can be set to illuminate with the high luminance so that the so-called 
"demonstration function" can be performed with an excellent visibility 
even if the surroundings are bright. 
Although the present invention has been described hereinbefore in 
connection with its first, second and third embodiments, it should not be 
limited to those embodiments. The following modifications can be attained 
according to the present invention. 
For example, the brightness of the light emitting element using the EL 
elements can also be controlled by changing not the amplitude of the AC 
voltage to be applied to the EL elements but the frequency of the AC 
voltage applied intermittently to the EL elements and changing the duty 
ratio. 
Moreover, the following functions can be effectively added to the timepiece 
equipped with the light emitting device according to the present 
invention. 
For example, the light emitting element is flashed with an arbitrary 
period. When the surroundings are so dark that the display of the 
timepiece cannot be observed, the light emitting element disposed in the 
display of the timepiece is caused to illuminate, as has been described 
hereinbefore. For the time recognition, it is not always necessary to 
cause the light emitting element to illuminate continuously, but the 
recognition can also be achieved by the flashing illumination with a 
suitable period. In these manners, the energy to be consumed by the light 
emitting element can be reduced. Incidentally, the flashing period may 
preferably be 1 to 2 seconds and can be achieved in an analog piece time 
by using motor driving pulse signals. 
[EFFECTS] 
(1) In the structure including switching means for switching a first mode, 
in which said light emitting element is caused to illuminate with a 
predetermined brightness when in the darkness where the brightness of the 
light detected by said light detecting means is lower than a predetermined 
brightness and not to illuminate when in the brightness where the detected 
brightness is higher than a predetermined brightness, and a second mode in 
which said light emitting element is caused to illuminate more brightly 
than the illumination in the darkness of said first mode, 
the light emitting element is normally enabled to illuminate automatically 
with a low luminance only in the darkness thereby to reduce the power 
consumption and, if necessary, to illuminate with a high luminance so that 
the so-called "demonstration function" can be achieved excellently visibly 
even if the surroundings are bright. 
(2) In the structure including switching means for switching a first mode, 
in which said light emitting element is caused to illuminate with a 
predetermined brightness when in the darkness where the brightness of the 
light detected by said light detecting means is lower than a predetermined 
brightness and not to illuminate when in the brightness where the detected 
brightness is higher than a predetermined brightness, and a third mode in 
which said light emitting element is caused to illuminate in the 
brightness more brightly than the illumination in the darkness in said 
first mode and in the darkness more darkly than the illumination in said 
brightness, 
the light emitting element is normally enabled to illuminate automatically 
with a low luminance only in the darkness thereby to reduce the power 
consumption and, if necessary, to illuminate with a high luminance so that 
the so-called "demonstration function" can be achieved excellently visibly 
even in the daytime. In case, moreover, the switching means is set in the 
third mode (i.e., the demonstration mode) when the surroundings are dark 
as in the nighttime, the light emitting element illuminates with the low 
luminance the power consumption can be reduced to a lower value than that 
of the foregoing first embodiment (in which the light emitting element 
always illuminates with the high luminance independently of the brightness 
of the surroundings). 
(3) In the structure including switching means for switching a fourth mode, 
in which said light emitting element is caused to illuminate the more 
darkly when in the darkness where the brightness of the light in 
accordance with the brightness of the surroundings detected by said light 
detecting means is lower than a predetermined brightness and not to 
illuminate when in the brightness where the detected brightness is higher 
than a predetermined brightness, and a fifth mode in which said light 
emitting element is caused to illuminate more brightly than the highest 
brightness of the illumination in said fourth mode, 
the light emitting element is normally enabled to illuminate with a low 
luminance only in the darkness in accordance with the brightness of the 
surroundings thereby to reduce the power consumption and, if necessary, to 
illuminate with a high luminance so that the so-called "demonstration 
function" can be achieved excellently visibly even if the surroundings are 
bright.