JPH0290453A - Low pressure mercury vapor discharge lamp - Google Patents

Abstract

PURPOSE:To eliminate brightness difference at the starting and achieve uniform brightness for whole area by reducing the resistance value per unit length of a heater at the region, where the light transmissivity due to the film thickness of a phosphor film is 25-40%, as compared to the other region. CONSTITUTION:In case where the surrounding atmosphere is at a low temperature, a current is supplied to a heater 20 to heat a bulb 6. The evaporation of sealed-in mercury is promoted and a predetermined vapor pressure is obtained, so that when a lamp 5 is turned on the light flux is built up rapidly and transition to stable lighting is achieved. In this case, a phosphor film 15 of the fluorescent lamp 5 has uneven thickness, and at the linear parts 8a, 8b of the bulb 6, the light transmissivity is 25-40% and the maximum brightness is obtained, but at the bent part 7 of U-shaped structure, the film thickness is thinner due to the bending process so that the brightness is somewhat lower. Accordingly, at the bent part 22a of a heater 20, the width W1 of a mesh heater 21 is made smaller to make the resistance value larger so as to make the heating value larger, and to the contrary, the width W2 at the linear part 22b is made larger than W1. In this way, the mercury vapor pressure is raised at the bent part 7 of the fluorescent lamp 5 to increase the brightness.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a low-pressure mercury vapor discharge lamp with improved start-up characteristics during lamp operation, particularly in a cold atmosphere.

(Prior technology) Liquid crystal meters used in automobile instrument panels display light on the liquid crystal surface by shining light from the back of the liquid crystal. A lighting device is needed that can illuminate the entire liquid crystal surface with uniform brightness.

Conventionally, this type of backlight includes a hot cathode or cold cathode fluorescent lamp housed as a light source in a casing that has a reflective surface on its inner surface, and the light from this lamp is reflected by the reflective surface and then exits from the opening of the casing. A lighting device that emits light is used.

When a hot cathode or cold cathode fluorescent lamp is used as the above light source, these fluorescent lamps have superior luminous efficiency, generate less heat, and have a longer lifespan than incandescent lamps.Moreover, they have a long discharge path, so their light emitting area is small. It has the advantage that it is large and the light distribution can be easily made uniform. In addition, in the case of a fluorescent lamp, it is easy to configure the discharge path into a curved shape, such as a U-shape or a W-shape, and the light-emitting surface becomes wider in plan, making it easier to uniformly illuminate a display surface with a predetermined spread. There are also advantages.

However, when a low-pressure mercury vapor discharge lamp, typically a fluorescent lamp, is turned on in a low ambient temperature,
The mercury vapor pressure sealed inside the bulb is low, so it is dark.
Moreover, it takes a long time for the mercury vapor pressure to increase and reach a predetermined brightness. That is, when the lamp is turned on in an extremely cold atmosphere, it takes a long time for the luminous flux to rise.

Automotive instrument panels are around +40°C to -30°C.
Therefore, when a fluorescent lamp is used as a backlight light source, it is necessary to take measures against the luminous flux rise characteristics.

In order to improve the rise time of the luminous flux, methods of heating the fluorescent lamp with a heater are being considered.

Such a heater is attached to the outer surface of the fluorescent lamp, and when the ambient atmosphere is low, it heats the bulb to increase the mercury vapor pressure, making it possible to obtain a predetermined brightness in a short time.

(Problems to be Solved by the Invention) However, when a heater is attached to the outer surface of a fluorescent lamp, the following problems occur if the heat generation performance of the heater is uniform along the axial direction of the lamp.

That is, in a fluorescent lamp, the thickness of the phosphor coating applied to the inner surface of the bulb may not be uniform over the entire surface.

In other words, in the case of a straight tube type bulb, the phosphor is applied to the inner surface by keeping the bulb in a vertical position and flowing a solution of phosphor powder from the top opening. Therefore, the film thickness tends to be thicker on the lower end side than on the upper end side.

In addition, in the case of a U-shaped bent bulb, a phosphor coating is formed on the straight bulb before the bulb is bent, and then the phosphor film is bent. The thickness of the body coat tends to become thinner.

On the other hand, in a fluorescent lamp, the light transmittance changes depending on the thickness of the phosphor coating. In other words, if the phosphor film is too thin, the ability to convert ultraviolet rays into visible light will be low, resulting in darkness; if the phosphor film is too thick, it will block the converted visible light. action occurs, and in this case it also becomes dark.

Therefore, it has been conventionally believed that the thickness of the phosphor film is the brightest when the light transmittance thereof is 25 to 40%, and this is also supported by experience.

However, as described above, since the thickness of the phosphor coating formed on the inner surface of the bulb is not uniform, an imbalance in brightness occurs throughout the lamp.

In other words, the light transmittance depending on the thickness of the phosphor coating is 25 to 4.
It is bright in the 0% area, and dark outside this area.

This difference in brightness is not noticeable when the lighting is stable, but
There is a problem in which there is a noticeable difference in brightness and darkness when the lamp starts up.

The present invention aims to provide a low-pressure mercury vapor discharge lamp that quickly starts up the dark part at the time of startup, eliminates the difference in brightness, and provides uniform brightness throughout.

[Structure of the invention]

(Means for Solving the Problems) The present invention provides that the resistance value per unit length of the heater is determined by the thickness of the phosphor film deposited on the inner surface of the bulb by 25% by the light transmittance.
The resistance value in the ~40% region is lower than that outside this region.

(Function) According to the present invention, in a dark place where the light transmittance is outside the range of 25 to 40%, the resistance value per unit length of the heater increases, so that this place is heated more strongly than in a bright place. Therefore, the vapor pressure in the darkened area at startup is promoted to rise, and the luminous flux rises quickly, so that the difference in brightness and darkness can be eliminated.

(Example) The present invention will be described below based on an example shown in FIGS. 1 and 2.

In the figure, 1 is a casing, which is made of synthetic resin such as polycarbonate, and is shaped like a quadratic curve in cross section. A partition protrusion 2 is integrally formed in the center of the bottom surface of the sink 1 along the longitudinal direction. As shown in FIG. 2, this protrusion 2 has a substantially triangular cross section.

The entire bottom surface and protrusion 2 of the casing 1 are made into a reflective surface 3.

A cold cathode fluorescent lamp 5 is accommodated in such a casing 1 . In this embodiment, a U-shaped cold cathode fluorescent lamp 5
is used.

That is, 6 is a valve bent into a U shape,
This valve 6 has straight portions 8a and 8b at both ends of a U-shaped bent portion 7, which are substantially parallel to each other.

Cold cathode type electrodes 9a are provided at the ends of these straight portions 8a and 8b.
.

9b is sealed, and a base 10a and a fob are attached.

A phosphor coating 15 shown in FIG. 2 is formed on the inner surface of the bulb 6, and a predetermined amount of mercury and a starting rare gas such as argon or xenon are sealed inside the bulb 6. ing.

Although not shown, the thickness of the phosphor coating 15 formed on the inner surface of the bulb 8 is the same as that of the straight portion 8a of the bulb 6.

In 8b, the coating is applied so that the light transmittance is the highest brightness of 25 to 40%, whereas in the U-shaped bent part 7, the film thickness becomes thinner due to the bending process, and the brightness decreases slightly. are doing.

A heater 20 is attached to such a fluorescent lamp 5. The heater 20 has a sheet shape, for example, and
It is formed along the pipe axis of the valve 6, that is, in a U-shape opposite to the valve shape, and is attached to the lower surface of the valve 6 toward the bottom surface of the casing 1.

Although not shown in detail, the heater 20 of this embodiment is formed by a mesh heater 21 formed by chemically etching a thin conductive plate made of stainless steel or the like into an elongated mesh body.

In this case, the width W1 of the mesh heater 21 is reduced at the portion facing the U-shaped bent portion 7 of the valve 6, that is, the bent portion 22a of the heater, and the portion facing the straight portions 8a, 8b of the valve 6. That is, the width W2 of the linear portions 22b and 22b of the heater is made larger than the width W1. In a heater, when the thickness is the same, increasing the width increases the cross-sectional area, resulting in a lower current resistance value per unit length.
In contrast, in the linear portions 22b and 22b of the heater, the current resistance value per unit length is set to be low and the amount of heat generated is small. .

Such a mesh heater 21 is laminated and reinforced with resin sheets 23 from both sides.

The heater 20 is mounted in close contact with the bulb 6 of the fluorescent lamp 5. When attaching the heater 20 closely to the bulb 6, it may be bonded with adhesive, but a transparent heat-shrinkable tube (not shown) is placed over the heater 20 and the bulb 6, and the whole is heated to make it heat-shrinkable. The heater 20 can also be held in close contact with the outer surface of the valve 6 by shrinking the tube.

Such a fluorescent lamp 5 is housed in the casing 1 with its straight portions 8a and 8b being substantially parallel to the bottom surface of the casing. In this case, the substantially parallel straight parts Ba and 8b of the U-shaped valve 6 are arranged along the protrusion 2, and the protrusion 2 is interposed between these straight parts 8a and 8b, that is, the protrusion 2 is installed so as to divide the space between the two adjacent straight parts 8a and 8b.

The fluorescent lamp 5 has caps 10a at both ends,
The lOb portion is attached to the casing 1 by being fitted into fixing notches 11a and llb formed in the side wall 4 of the casing 1 and fixed by appropriate means such as adhesive.

A light diffusing and transmitting plate 12 is attached to the upper opening of the casing 1 . This light diffusing and transmitting plate 12 is made of acrylic resin or the like and has a milky white color and has a light diffusing effect. A portion 13 is formed.

The thickness of this thick wall portion 3 gradually becomes thinner as it moves away from the valve 6.

The operation of the lighting device having such a configuration will be explained.

When the surrounding atmospheric temperature is low, the heater 20 is energized to heat the bulb 6. Then, the evaporation of the encapsulated mercury is promoted and a predetermined vapor pressure is reached, so that when the lamp 5 is turned on, the luminous flux quickly rises and stable lighting is achieved.

In this case, the thickness of the phosphor coating 15 of the fluorescent lamp 5 is not uniform, and the straight portions 8a and 8b of the bulb 6 have the highest brightness with a light transmittance of 25 to 40%. In the U-shaped bent portion 7, the film thickness is thinner due to the bending process, and the brightness is slightly lowered.

This difference in brightness is not noticeable when the lighting is stable, but
There is a clear brightness and darkness when the lamp starts up, and this is a noticeable problem.

On the other hand, in this embodiment, the width wl of the mesh heater 21 is made small in the bent part 22a of the heater 20, and therefore the resistance value is increased to increase the amount of heat generated. In 22b, its width W
2 is made larger than the above-mentioned width W1 to lower the resistance value and the amount of heat generated.

Therefore, in the valve 6, the bent portion 7 is heated at a greater rate by the heater 20 than the straight portions 8a and 8b, which promotes an increase in the mercury vapor pressure in the bent portion 7.

Therefore, at the bent portion 7, the amount of ultraviolet radiation is increased and the brightness of this portion increases, so that the brightness of the entire lamp along the axial direction becomes uniform.

In particular, the difference in brightness and darkness at the time of lamp startup is eliminated, and problems such as conspicuous differences are eliminated.

In this way, when the fluorescent lamp 5 is turned on, the light emitted from the lamp 5 is directed directly and after being reflected by the reflective surface 3 to the opening of the casing l, and the light emitted from the lamp 5 is directed to the opening of the casing l. The light is diffused by the diffuser-transmitting plate 12 and irradiated to the outside.

In this case, since the reflective surface 3 of the casing 1 has a quadratic curved surface, the light reflected by the reflective surface 3 has approximately equal brightness at the opening of the casing 1. Since the protrusion 2 is interposed between the substantially parallel straight parts 8a and 8b of the U-shaped bulb 6, the protrusion 2 reflects the light emitted from the straight parts 8a and 8b, respectively. The light is reflected upward to increase the brightness on the light diffusing and transmitting plate 12.

Further, since the thick part 13 is formed on the inner surface of the light diffusing and transmitting plate 12, the thick part 13 faces directly above the bulb 6, and this thick part reduces the amount of light transmitted. As the distance from the wall increases, the wall thickness decreases, increasing the amount of light transmitted.

Because of this, uneven brightness over the entire surface of the light diffusing and transmitting plate 12 is eliminated.

Note that since the heater 20 is attached to the lower surface of the bulb 6, even if the heater 20 blocks some light, there is no problem as long as it is oriented in this direction.

Note that the present invention is not limited to the above embodiments.

That is, the heater 20 is not limited to a laminate heater in which the mesh heater 21 is laminated with a resin sheet 23, but may be a printed resistor heater, a linear heater, or the like.

Therefore, the heater is not restricted in shape or material.

Furthermore, the heater 20 is not limited to being attached directly to the bottom surface of the valve 6, but may be arranged along the shape of the valve 6 by being fixed to the bottom surface of the casing 1, as shown in FIG. It's okay.

In the case of the above embodiment, the thickness of the phosphor coating is such that the light transmittance is 25 to 40 in the straight portions 8a and 8b of the bulb 6.
%, and the U-shaped bent portion 7 is made thinner than this. Therefore, the bent portion 22a of the heater 20 has a high resistance value per unit length, and the straight portions 22a and 22b are made thinner. Although the resistance value per unit length was lowered in the above example, the thickness of the phosphor coating can be controlled during manufacturing, so contrary to the above, the U-shaped bent portion 7 has a light transmittance of 25 to 40%. On the other hand, the thickness of the film may be thicker on the straight portions 8a and 8b, and in such a configuration, the heater 2
0, the straight portions 22b and 22b have the bent portion 2
The difference in brightness can be resolved by increasing the resistance value and increasing the amount of heat generated compared to 2a.

Further, the present invention is not limited to U-shaped fluorescent lamps, and may be applied to W-shaped or ring-shaped fluorescent lamps, as well as straight-tube fluorescent lamps, as described above. Since a difference occurs, the present invention can be applied.

As mentioned above, in the present invention, the resistance value of the heater is not determined based on whether the thickness of the phosphor coating is thick or thin, but is determined based on whether the light transmittance is in the range of 25 to 40%. If the film is out of this range, the resistance value of the heater increases regardless of whether the film is thick or thin.

Furthermore, the present invention is not limited to cold cathode fluorescent lamps, but may also be applied to hot cathode fluorescent lamps.

〔Effect of the invention〕

As explained above, according to the present invention, due to the difference in the thickness of the phosphor coating, the resistance value per unit length of the heater is increased in dark areas where the light transmittance is outside the range of 25 to 40%. As a result, this area is heated strongly, which promotes a rise in vapor pressure in the area that becomes dark at startup, and the luminous flux rises quickly, making it possible to achieve the same brightness as the dark area mentioned above. It is possible to eliminate the difference in brightness and darkness.

[Brief explanation of the drawing]

1 and 2 show one embodiment of the present invention, FIG. 1 is an exploded perspective view of the entire lighting device, FIG. 2 is a sectional view of the assembled state, and FIG. 3 is another embodiment of the present invention. It is a sectional view showing an example. ■... Casing, 3... Reflective surface, 5... Cold cathode fluorescent lamp, 6... Bulb, 7... Bent portion of bulb, 8a. 8b... Straight portion of bulb, 9as 9b... Cold cathode, 12... Light diffusing and transmitting plate, 20... Heater, 21...
...Mesh heater, 22a...Bent part of heater, 2
2b... Straight line part of the heater. Applicant's agent Patent attorney Takehiko Suzue

Claims (1)

[Claims] In a low-pressure mercury vapor discharge lamp in which a heater is attached along the axial direction of the bulb and the heater heats the bulb to promote an increase in mercury vapor pressure, a phosphor coated on the inner surface of the bulb. Light transmittance depending on film thickness is 25-4
A low-pressure mercury vapor discharge lamp characterized in that in a region of 0%, the resistance value per unit length of the heater is lower than in locations outside this region.