JPH10199480A - Lighting system and display device having the system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To quicken brightness standing at low temperature, eliminate use of a heater for starting, simplify constitution, and reduce cost by adequately setting the dimension of a glass tube of a florescent part, and setting a heat capacity per length of the glass tube in the specified value or lower. SOLUTION: A display device 100 comprises a transmission type display element 8 such as a liquid crystal display element, and a lighting system 110 which illuminates the display element 8 from the back side and has a small heat capacity, high heat cold cathode fluorescent tube 1. In the small heat capacity, high heat cold cathode fluorescent tube 1, the thickness dt of a glass tube to the inner diameter da=0.20cm of the glass tube is set thin, for example to dt=0.03cm, and heat capacity per length (1cm) of the glass tube of 0.035Wsec/ deg.C is obtained. By making the heat capacity of the glass tube small, the glass tube is quickly heated by heat energy generating by emission of gas sealed, and brightness standing at low temperature is quickened.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a lighting device having a cold cathode fluorescent tube and a display device provided with the same.

[0002]

2. Description of the Related Art Conventionally, in a liquid crystal display device such as a display device of a vehicle-mounted navigator, a vehicle-mounted television, or a vehicle-mounted meter, a direct-type backlight or an edgelight-type lighting device has been widely used. A cold cathode fluorescent tube is used as a light source of a lighting device for these liquid crystal display devices. Cold-cathode fluorescent tubes have the advantages of higher luminous efficiency, less heat generation, longer life, moreover, a thin shape and a better luminance (luminous flux) distribution than incandescent lamps.

[0003] However, the conventional general cold-cathode fluorescent tube has a problem that its characteristics are affected by the ambient temperature. This is because the characteristics of the conventional cold cathode fluorescent tube depend on the vapor pressure of mercury sealed therein. The most significant influences are low-temperature luminance (luminous flux) rising characteristics (starting characteristics) and low-temperature luminance. For example, lighting devices for vehicles are used in a wide temperature range from about 40 ° C. to 30 ° C. below freezing (tropical or polar). The conventional cold cathode fluorescent tube described above has an ambient temperature of about 4
The luminous efficiency is maximized at 0 ° C, and there is no practical problem in a temperature range of about 5 to about 40 ° C. However, when used at a low temperature, for example, at around 30 ° C. below freezing, there is a problem that it takes a long time to reach a predetermined luminance or it is difficult to light.

In order to improve the luminance rise at low temperatures and the luminance at low temperatures, Japanese Patent Application Laid-Open No. 63-224140 discloses a self-temperature control type heating element for increasing the surface temperature of a cold cathode fluorescent tube. It discloses a configuration provided around a fluorescent tube. Japanese Patent Application Laid-Open No. 7-43680 discloses that a heater for warming a cold cathode fluorescent tube is provided, and the surface temperature of the cold cathode fluorescent tube is constantly measured using a temperature detecting element and a temperature detecting circuit. Is disclosed to control the power supplied to the heater by controlling the power.

Further, as another method, a method has been proposed in which the current flowing through the cold cathode fluorescent tube is increased only at the start of lighting to improve the rise of luminance at low temperatures. For example, Japanese Unexamined Patent Publication No. Sho 61-74298 discloses a configuration provided with a control means for increasing the cold cathode fluorescent tube current from a rated value for a certain period of time within a luminance rising period from lighting.

Further, Japanese Patent Application Laid-Open No. 59-60880 discloses a method of increasing the cutoff current of a switch circuit for a certain period of time from the time of starting to increase the energy of a cold cathode fluorescent tube.

[0007]

However, the above-mentioned prior art has the following problems.

In the method of using a self-temperature control heating element or a heater to heat a cold cathode fluorescent tube, the method itself is in close contact with the surface of the cold cathode fluorescent tube and blocks the light beam of the cold cathode fluorescent tube. However, there is a problem that the loss of light is large and the amount of illumination light is reduced. In addition, there is a problem that when the control circuit of the heater malfunctions, thermal runaway of the heater occurs. Further, since related parts including the heater itself and the control circuit are required in addition to the conventional constituent parts, the cost is greatly increased. In addition, extra power (typically several tens of watts) to be supplied to the heater is required, and the load on the battery is reduced especially when lighting a lighting device of a car whose battery temperature is below freezing in winter. Of course, the effect on the car itself cannot be ignored.

In the method of improving cold start by increasing the current of the cold cathode fluorescent lamp for a certain period of time from the start, a current larger than the rated value flows at the start, so that the cold cathode fluorescent tube is greatly damaged and the cold cathode fluorescent lamp is damaged. There is a problem that the life of the tube is shortened. In addition, this method does not have a sufficient effect of improving the luminance rise at a low temperature as compared with the above-described method using a heater, and is often used in combination with a method using a heater.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a lighting device having excellent operating characteristics at low temperatures and a display device using the lighting device. It is in.

[0011]

The lighting device of the present invention has a cold cathode fluorescent tube having a heat capacity per unit length (1 cm) of the glass tube of the fluorescent portion of 0.035 Wsec / ° C. or less. The above object is achieved by the above.

A structural factor time constant τ s given by a product of a heat capacity (Wsec / ° C.) C and a thermal resistance (° C./W) R per unit length (1 cm) of the glass tube of the fluorescent portion of the cold cathode fluorescent tube. Is 11 seconds or less, and R = (Ts−T) / ｛(Vc
cft−Vp) · Iccft / L｝, and Vccft
Is a fluorescent tube voltage (Vrms), Vp is a fluorescent tube electrode voltage drop (Vrms), Iccft is a fluorescent tube current (Arms),
L is the length of the fluorescent tube (cm), T is the ambient temperature (° C), Ts
Is the saturated tube wall temperature (° C.), and is preferably the temperature when the temperature of the tube wall of the cold cathode fluorescent tube reaches a steady state with the cold cathode fluorescent tube turned on.

The cross-sectional area of the glass tube of the cold cathode fluorescent tube is Dt.
(Mm ^2), Dg the filling gas cross sectional area (mm ^2), when the glass tube inner diameter ^{da (mm 2), Dt /} Dg <2 / d
More preferably, the relational expression a is satisfied.

The calorific value Wv (W) per unit volume (1 cm ³ ) of the glass tube of the fluorescent portion of the cold cathode fluorescent tube and the fluorescent tube current Iccft (mArms) are Wv / Icc.
It is preferable to satisfy the relationship of ft ≧ 0.5.

The time constant τ at which the luminance of the cold cathode fluorescent lamp rises is from −10 ° C. of the lighting start ambient temperature T (° C.) to +2.
In the range of 5 ° C., τ ≦ −0.0006T ³ +0.0
It is preferable to satisfy the relationship of 288T ² −0.4668T + 26.8.

The pre-exponential factor A (percentage of the saturated relative luminance to the pre-exponential factor A 0) of the luminance rise characteristic of the cold cathode fluorescent tube is within the range of A ≧ 0.
It is preferable to satisfy the relationship of 92T + 60.

[0017] It is preferable that the activation energy of the cold cathode fluorescent tube in the ambient temperature range of the lighting start of the exponential factor is 3.0 kcal / mol or less.

9 of the total surface area of the fluorescent portion of the cold cathode fluorescent tube
Preferably, 5% or more is in contact with air, and 50% or more of the light from the cold cathode fluorescent tube is used for illumination.

It is preferable that a selective polarizing sheet is further provided on the light emission side of the cold cathode fluorescent tube.

In the operating state, a constant current may be supplied to the cold-cathode fluorescent tube, and a temperature detector for detecting an ambient temperature of the cold-cathode fluorescent tube, and a temperature detected by the temperature detector And a calculating device for setting a predetermined tube current based on the current, and the tube current supplied to the cold cathode fluorescent tube may be controlled based on the lighting start ambient temperature.

The lighting device of the present invention has a temperature detecting step of detecting an ambient temperature of the cold cathode fluorescent tube, and a step of setting a predetermined tube current based on the temperature detected by the temperature detector. In this case, the light-emitting device may be driven by a method including a step of controlling a tube current supplied to the cold-cathode fluorescent tube on the basis of the ambient temperature at which the lamp is started.

A display device according to the present invention includes:
Having a transmissive display element that receives light from the lighting device,
Thereby, the above object is achieved. In one embodiment, the transmissive display device is a liquid crystal display device.

The operation of the present invention will be described below.

The cold cathode fluorescent tube provided in the lighting device of the present invention has a smaller heat capacity than a conventional cold cathode fluorescent tube. The energy applied to the cold cathode fluorescent tube is released not only as light emission but also as heat.Therefore, by reducing the heat capacity of the cold cathode fluorescent tube, the heat generated from the cold cathode fluorescent tube itself is used to cool the cold cathode fluorescent tube. The cathode fluorescent tube can be heated quickly.

Further, since the cold cathode fluorescent tube provided in the lighting device of the present invention generates a larger amount of heat than the conventional cold cathode fluorescent tube, the cold cathode fluorescent tube is heated quickly.

Further, by providing the polarization selective reflection sheet, light emitted from the cold cathode fluorescent tube can be efficiently used for illumination.

[0027]

Embodiments of the present invention will be described below. FIG. 1 shows a display device 100 according to the present invention. FIG.
(A) is a schematic diagram of the display device 100 and the display device 10.
0 includes a lighting device 110 and a transmissive display element (for example, a liquid crystal display element) 8.

FIG. 1B is a cross-sectional view of the illumination device 110 of the display device 100 taken along line 1B-1B. Lighting device 110
Are a small heat capacity high heat type cold cathode fluorescent tube 1 described later, a reflection sheet 2, a light guide 3, a diffusion sheet 4, a prism sheet (for example, a 3M BEF sheet) 5, a selective polarization reflection sheet 6, and a diffusion sheet. The seat 7 is provided. The difference between the lighting device 110 of the present invention and the conventional lighting device is that the lighting device 110 has the small heat capacity and high heat generation type cold cathode fluorescent tube 1 and the selective polarization reflection sheet 6.

The small heat capacity, high heat generation type cold cathode fluorescent tube 1 is a cold cathode fluorescent tube having a smaller heat capacity and a larger calorific value than a conventional cold cathode fluorescent tube. In the configuration shown in FIG. 1, most of the surface of the fluorescent portion of the cold cathode fluorescent tube 1 is in contact with air, and is thereby sufficiently insulated from other components. The feature of high heat generation with a small heat capacity of 1 is fully utilized. In order to obtain a sufficient heat insulating effect, it is necessary to reduce the total surface area of
Preferably 5% or more is in contact with air, about 98%
More preferably, at least% are in contact with air. Further, it is preferable from the viewpoint of utilization efficiency that 50% or more of the light from the cold cathode fluorescent tube 1 is guided to the light guide 3 and used for illumination. The arrangement of the cold cathode fluorescent tubes 1 is determined in consideration of light use efficiency and heat insulation.

The selective polarization reflection sheet 6 may be disposed between the diffusion sheet 4 and the prism sheet 5, and the diffusion sheet 7 may be omitted. Further, the selective polarization reflection sheet 6 can be omitted depending on the application. When a display element that uses only specific linearly polarized light, such as a liquid crystal display element, is used, the luminance can be improved by using the selective polarization reflection sheet 6.

Hereinafter, features of the illumination device and the display device of the present invention will be described in detail. The lighting device and the display device of the present invention are not limited to the above-described configurations, and as will be understood from the following description, components having individual characteristics can be used individually according to the application.

(Small Heat Capacity Cold Cathode Fluorescent Tube) The lighting device of the present invention includes a cold cathode fluorescent tube having a small heat capacity. The small-heat-capacity cold-cathode fluorescent tube suppresses heat energy generated inside the cold-cathode fluorescent tube from being released to the outside, so that the cold-cathode fluorescent tube itself can be rapidly heated.

Normally, the heat energy emitted by the cold cathode fluorescent tube itself is absorbed and propagated by the glass tube forming the cold cathode fluorescent tube, and is not effectively used for heating the cold cathode fluorescent tube. This is because the heat capacity of the glass tube forming the conventional cold cathode fluorescent tube is too large for the calorific value of the cold cathode fluorescent tube.

By reducing the heat capacity of the glass tube used for the cold cathode fluorescent tube, the glass tube warms up quickly,
It is possible to quickly warm the inside of the cold cathode fluorescent tube. In the small-heat-capacity cold-cathode fluorescent tube of the present invention, the heat capacity C per unit length (1 cm) of the glass tube is represented by the following equation (1), and the heat capacity C is 0.035 Wsec. / ℃
Refers to the following. In particular, the inner diameter da of the glass tube is preferably 0.20 cm or less.

[0035]

C = 4.2 · (π / 4) · {(db ² −da ² ) · s1 · δ1} (1) where C is the heat capacity (Wsec / ° C.) of the glass tube. db
Is the outer diameter of the glass tube (cm), da is the inner diameter of the glass tube (c
m), s1 is the specific heat of the glass material (cal / g · ° C.), δ
1 represents the density (g / cm ³ ) of the glass material, respectively.

Table 1 below shows typical values of the glass tube of the cold cathode fluorescent tube used in the present invention and the conventional glass tube. The numerical values in Table 1 indicate the numerical values per unit length (1 cm) of the glass tube, but in the experiment, the distance between the electrodes was 1 unit.
A 5 cm glass tube was used.

[0037]

[Table 1] Characteristic value Present invention Conventional example C (Wsec / ° C) 0.0290 0.0526 C (cal / ° C) 6.92E-3 1.25E-2 db (cm) 0.26 0.30 da (cm) 0. 20 0.20 Glass thickness (cm) 0.03 0.05 s1 (cal / g. ° C.) 0.14 0.14 δ1 (g / cm ³ ) 2.28 2.28 As shown in Table 1. The heat capacity C of the cold cathode fluorescent tube of the present invention
Is about 55% of the heat capacity of the conventional cold cathode fluorescent tube, which is very small. As a result, the cold cathode fluorescent tubes themselves are efficiently heated by the heat generated by the cold cathode fluorescent tubes during startup,
The rising characteristic of the luminance is improved.

The preferable heat capacity range of the cold cathode fluorescent tube used in the present invention can be expressed by a simpler relational expression. Regarding the cross section of the cold cathode fluorescent tube, the cross-sectional area of the cold cathode fluorescent tube in which gas is sealed is defined as Dg (determined by the inner diameter of the glass tube), and the cross-sectional area of the glass tube of the cold cathode fluorescent tube is defined as Dt (outside of the glass tube). If the cold cathode fluorescent tube has the same Dg (if the amount of heat energy generated from the sealed gas is the same), it is better to use a cold cathode fluorescent tube with a small Dt. The heat generated from the cold cathode fluorescent tube itself can be efficiently used to warm the tube itself. That is, Dt / D
It is more advantageous to use a cold cathode fluorescent tube having a small value of g.
Table 2 shows these parameters for the cold cathode fluorescent tubes shown in Table 1.

[0039]

[Table 2] The present invention Dg (mm ² ) 3.14 3.14 Dt (mm ² ) 2.167 3.925 Dt / Dg 0.69 1.25 The cold cathode fluorescent tube used in the present invention is a Dt / Dg. Those having a value of 1.0 or less are preferred. This relationship is Dt / Dg
It can be generalized to the relationship of <2 / da (in mm). Furthermore,
It is preferable that the surface area of the glass tube is small in order to reduce the heat energy loss caused through the surface of the glass tube of the cold cathode fluorescent tube. Further, the glass tube is preferably insulated by air without contacting other members.

Next, the result of the study on the thermal resistance R of the glass tube will be described. The thermal resistance R of the glass tube is represented by the following equation (2).

[0041]

R = 1 / K (2) K = (hw + hr · ηo) · π · db (theoretical formula) K = {(Vccft−Vp) · Iccft / L} / (Ts−T) ( Where R is the thermal resistance (° C./W) and K is the thermal conductivity (W /
° C), hw is the heat dissipation coefficient by convection (W / ° C
m ² ), hr is the heat dissipation coefficient due to radiation (W / ° C.
m ² ), η o is the ratio of that of the material to the radiation coefficient of the perfect black body, db is the outer diameter (cm) of the glass tube, Vccf
t is the fluorescent tube voltage (Vrms), Vp is the fluorescent tube electrode voltage drop (Vrms), and Iccft is the fluorescent tube current (Arm).
s) and L are the length (cm) of the fluorescent tube, Ts is the saturated tube wall temperature (° C), and T is the ambient temperature (° C). Saturated tube wall temperature Ts
The term “temperature” refers to a temperature when the temperature of the tube wall of the cold cathode fluorescent tube reaches a steady state with the cold cathode fluorescent tube turned on. In general, it is impossible to find K from the above theoretical formula,
K was determined based on the above empirical formula.

With respect to the glass tube having a db of 0.26 cm shown in Tables 1 and 2, Vp is 150 V and L is 16.5 c
When m and T are 25 ° C., the thermal resistance R is calculated by the above equation (2).
Table 3 shows the results obtained by changing Vccft, Iccft, and T using the empirical formula (1).

For a glass tube with a db of 0.30 cm, K is a heat dissipation coefficient hw due to convection of -1 / 1 / db of db.
Since it is proportional to the fourth power, K according to the above theoretical equation is db
Since it is proportional to the (3/4) power of (outer diameter of glass tube), it was obtained by multiplying an experimental value for db of 0.26 cm by a conversion coefficient of 1.113. The results are shown in Table 3.

[0044]

[Table 3]

As is apparent from the results in Table 3, the thermal conductivity of the cold cathode fluorescent tube of the present invention is smaller than that of the conventional cold cathode fluorescent tube by 10% or more, and it is difficult to radiate heat. That is, it can be seen that when the calorific value from the cold cathode fluorescent tube is the same, the cold cathode fluorescent tube itself can be more efficiently heated.

Next, the result of the study on the time constant of the rise of the luminance of the cold cathode fluorescent tube will be described. Time constant τs of rise of glass tube per unit length (1cm)
Is given by Equation (3) shown in (Equation 3) using the heat capacity C and the heat resistance R per unit length (1 cm) of the glass tube. Since this time constant is a time constant determined by the structure of the cold cathode fluorescent tube, it is particularly represented as a structure factor time constant τs.

[0047]

Τs = C · R (3) Table 4 shows the results obtained for the above-described cold cathode fluorescent tubes of the present invention (db is 0.26 cm) and the conventional example (db is 0.30 cm). Show

[0048]

[Table 4] Present invention db = 0.26 db = 0.30 τs (sec) 9.08 14.77 C (Wsec / ° C) 0.00291 0.00526 R (° C / W) 312.3 280.5 The value of R is , From the value of K in Table 3. As is clear from the results in Table 4, τs of the cold cathode fluorescent tube according to the present invention was
It can be seen that has a structure that is much shorter than the conventional example and is easily heated. The τs of the cold cathode fluorescent tube suitably used in the present invention is preferably 11 sec or less.

Regarding the present invention and the conventional cold cathode fluorescent tube,
Actual brightness rise time constant τ at various ambient temperatures
FIG. 2 and Table 5 show the results obtained (actual measurement values, unit seconds). This τ is called an actual measurement time constant. In FIG. 2, τh,
τj indicates actual measurement time constants of the cold cathode fluorescent tubes of the present invention and the conventional example, respectively.

[0050]

[Table 5] Ambient temperature (° C.) of the present invention Conventional example db = 0.26 db = 0.30 −20 −10 30.0 48.0 0 21.8 43.3 25 18.0 34.5 As is clear from the results in Table 5, the present invention It can be seen that the cold cathode fluorescent tube of the present invention has a shorter τ compared to the conventional example, and is heated in a short time. As described above, τs can be used for relative evaluation of the luminance rise characteristics of the cold cathode fluorescent tube, but the value of τs in Table 4 is different from the value of τ in Table 5, and It can be seen that the actual time constant of the luminance rise cannot be accurately evaluated only by the structure.

In FIG. 2, the range of the time constant τ suitably used for the cold cathode fluorescent tube of the present invention was determined. FIG. 2 shows a preferable boundary curve of τ obtained based on a curve (curve fitting) obtained by approximating a measured value by a third-order polynomial. Area below this boundary curve (τ ≦ −0.0006)
^{T 3 + 0.0288T 2 -0.4668T + 26.8} , T
Is preferably ambient temperature / ° C.).

Further, the result of studying the dependence of τ of the cold cathode fluorescent tube on the ambient temperature will be described below. The time dependency I (t) of the brightness of the cold cathode fluorescent lamp at the time of rising is expressed by the following equation (4).

[0053]

I (t) = A · {1−exp (−t / η · C · R)} + B · t (4) η = τ / C · R where I (t) is , The luminance of the cold cathode fluorescent tube at time t (cd / m ² ), A is the saturation luminance at the ambient temperature at the start of lighting (cd / m ² ), and η is a coefficient indicating the above-mentioned relationship between τ and τs. Indicates the present invention ηj is a conventional example, and B
Is the brightness increase rate coefficient (cd / m ² sec) of the cold cathode fluorescent tube.
c). Table 6 shows the results obtained for the above-described cold cathode fluorescent tubes of the present invention and the conventional example.

[0054]

[Table 6] Present invention db = 0.26 Conventional example db = 0.30 Ambient temperature (° C.) ηh ηj -20 -10 3.3 3.2 0 2.4 2.9 25 2.0 2.3 As is clear from the results in Table 6. , Η also vary with temperature.

Next, the pre-exponential factor A in the above equation (4)
Temperature dependence was studied. The pre-exponential factor A is expressed by the following equation (5), and the activation energy ΔE
I asked.

[0056]

A = A0 · exp (−ΔE / kb · T) (5) where A0 is a pre-exponential factor of saturation relative luminance, ΔE is activation energy (kcal / mol), and kb is Boltzmann. The constant, T, is the lighting start ambient temperature (° C.).

The experimental results, their Arrhenius plots, and ΔE obtained therefrom indicate the activation energies shown in FIGS. 3, 4, 7 and 8, respectively. The value in the table is A
Expressed as a percentage of 0.

[0058]

[Table 7] T (° C.) The present invention Ah Aj (conventional example) -20 50% -10 61% 14% 0 71% 25 92% 68%

[0059]

[Table 8] Present Invention Conventional Example ΔE (kcal / mol) 2.0 7.0 As can be seen from the above results, the activation energy of the cold cathode fluorescent tube according to the present invention is much smaller than that of the conventional example,
It can be seen that it has stable thermal characteristics over a wide temperature range. Further, as a result of various studies, the activation energy of the cold cathode fluorescent tube suitably used in the present invention is from −10 ° C.
3.0 kcal / mol at an ambient temperature of + 25 ° C.
The following is preferred. The pre-exponential factor A preferably satisfies A ≧ 0.92T + 60 within the above temperature range.

FIGS. 5 and 6 show the results of measuring the luminance rise characteristics of the cold cathode fluorescent tubes of the present invention and the conventional example at various ambient temperatures. As evident from these figures,
It can be seen that the luminance rise characteristics of the lighting device of the present invention are much better than those of the related art.

(High heat generation type cold-cathode fluorescent tube) In order to ensure a sufficient luminance start-up at low temperatures, illumination using a cold-cathode fluorescent tube which generates a larger amount of heat than a conventional cold-cathode fluorescent tube. It can be solved by making the device. If the calorific value of the cold cathode fluorescent tube is increased, mercury in the cold cathode fluorescent tube is warmed and mercury vapor is significantly increased, and as a result, the brightness of the lighting device is increased. In order to increase this calorific value, roughly
There are two ways. The first method is to increase the gas pressure of the cold cathode fluorescent tube compared to the conventional one. Second
Is to increase the mixing ratio of the argon gas in the sealed gas in the cold cathode fluorescent tube.

The reason why the calorific value of the cold cathode fluorescent tube increases when the gas pressure of the cold cathode fluorescent tube is increased in the first method will be described below. The mean free path of the ionized atoms moving in the cold-cathode fluorescent tube is shortened, and the number of collisions between the atoms is increased as compared with the conventional cold-cathode fluorescent tube. As a result, the calorific value increases. In the present invention, the gas pressure is preferably about 100 Torr or more, and more preferably about 120 Torr or more.

In the second method, the reason why the heating value of the cold cathode fluorescent tube increases when the mixing ratio of the argon gas in the filling gas in the cold cathode fluorescent tube increases will be described below. Usually, a mixed gas of neon gas and argon gas is sealed in the cold cathode fluorescent tube. Since the argon gas is approximately twice as heavy as the neon gas in comparison with the neon gas, the heat generated when the argon gas collides is larger than the neon gas. Therefore,
By increasing the ratio of the argon gas, the calorific value of the cold cathode fluorescent tube can be increased.

In the present invention, the calorific value is increased by setting the ratio of argon gas / neon gas to about 40/60 or more. The gas pressure of the cold cathode fluorescent tube of the present invention shown in FIGS. 7 to 10 is 120 Torr, and the ratio of argon gas / neon gas is 40/60. The gas pressure of the conventional cold cathode fluorescent tube is 60 Torr, and the ratio of argon gas / neon gas is 5/95.

As shown in FIGS. 7 and 8, it is understood that the calorific value (per unit length and per unit volume) with respect to the tube current is superior to that of the conventional cold cathode fluorescent tube of the present invention. Preferred characteristics of the cold-cathode fluorescent tube suitably used in the present invention include a heating value per unit volume of Wv
(W), and when the fluorescent tube current is Iccft (mArms), it is preferable that Wv / Iccft ≧ 0.5. This corresponds to the upper part of the straight line in FIG.

FIG. 9 shows the relationship between the fluorescent tube current and the fluorescent tube voltage for the cold cathode fluorescent tube of the present invention and the conventional cold cathode fluorescent tube. It can be seen that the cold cathode fluorescent tube of the present invention has a higher fluorescent tube voltage than that of the conventional example. FIG. 10 shows the fluorescent lamp power consumption of the cold cathode fluorescent tube of the present invention and the conventional cold cathode fluorescent tube. As is clear from FIG. 10, the cold cathode fluorescent tube of the present invention consumes more power than the conventional one. As described above, since the cold cathode fluorescent tube of the present invention consumes a large amount of power in the positive column, it can be seen that the calorific value of the fluorescent portion due to gas is larger than that of the conventional cold cathode fluorescent tube.

(Control Method of Cold Cathode Fluorescent Tube) The control method will be described by taking, as an example, a case where the lighting device according to the present invention is applied to an in-vehicle display device. As described above, the cold-cathode fluorescent tube according to the present invention has excellent luminance rising characteristics, and therefore does not need to be boosted at the time of low-temperature startup as in the related art. However, by boosting, it is of course possible to further improve the luminance rise characteristics at low temperatures. In the following description, the case where boost is used together will be described.

For example, the operation mode is selected according to the ambient temperature of the display device mounted on the vehicle. If the ambient temperature is significantly lower (e.g., around -30 [deg.] C.) than the temperature range controlled by air conditioning in the vehicle (e.g., around -30 [deg.] C.), a current higher than the rated current (e.g., 4 mA Arms) (e.g., 5 mA Arm).
s) for a short time. When the temperature is equal to or higher than the temperature range controlled by the air conditioning, the rated current may be supplied from the start.

This operation mode selection is executed, for example, by the control circuit system shown in FIG. 11 according to the flow shown in FIG. The ambient temperature is measured by a temperature detector provided near the display device, the arithmetic device receives the ambient temperature, determines the setting of the tube current, and sends a signal to the drive device so that the rated current or the boost current flows. give. The driving device that has received the signal starts operation so as to supply a predetermined tube current to the lighting device, and the cold cathode fluorescent tube is turned on.

(Selective Polarization Reflecting Sheet) The polarization direction of the light emitted from the illumination device is controlled, the polarization direction is changed to the optimal polarization direction for the display device, the light use efficiency is increased, and the system can have high brightness. There is a method. This method is roughly classified into two methods.

A first method is to use a selective polarization reflection sheet that reflects the S-polarized light component and transmits the P-polarized light component. For details of the structure, see JP-A-6-51399.
Is disclosed.

The second method is a method using a selective polarization reflection sheet and a λ / 4 plate that reflects left circularly polarized light components and transmits right circularly polarized light components. Details of the structure are disclosed in U.S. Pat. No. 5,506,704.

These sheets effectively contribute to an increase in luminance when the display device provided on the lighting device uses polarized light (for example, a liquid crystal display device).

[0074]

【Example】

(Example 1) As Example 1, a display element for displaying by utilizing polarized light is mounted on an illuminating device having the structure shown in FIG. 1 and not using the selective polarization reflection sheet 6, and is shown in Table 9 and FIG. As shown in FIG. 13A, the luminance rise characteristic at −30 ° C. when the current flowing through the cold cathode fluorescent tube having a small heat capacity and a high heat generation is fixed at 4.5 mArms is shown in FIG. Table 9
The following summarizes the cold cathode fluorescent tube current and the conditions for the presence or absence of the selective polarization reflection sheet in the examples and comparative examples.

(Embodiment 2) As Embodiment 2, a display device for displaying by using polarized light is mounted on an illuminating device using the selective polarization reflection sheet 6 using linearly polarized light in the structure of Embodiment 1, and As shown in FIGS. 9 and 13 (b), FIG. 13 (a) shows the luminance rise characteristics at −30 ° C. when the current flowing through the small heat capacity, high heat generation type cold cathode fluorescent tube is constant at 4.5 mArms. .

(Example 3) As Example 3, an illuminating device in which the selective polarization reflection sheet 6 using linearly polarized light used in Example 2 was replaced with a selective polarization reflection sheet using circularly polarized light was used.
-30 ° C. when a display element for displaying light using polarized light is mounted and the current flowing through the cold cathode fluorescent tube having a small heat capacity and a high heat generation is fixed at 4.5 mArms as shown in Table 9 and FIG. FIG. 13A shows the luminance rise characteristics at the time of FIG.
Shown in

Example 4 As Example 4, as shown in Table 9 and FIG. 13B, the tube current of the small heat capacity, high heat generation type cold cathode fluorescent tube in the structure of Example 1 was measured for one minute after the start of lighting. In the figure, the current of the cold cathode fluorescent lamp is slightly larger, 6.0 mArms.
The cold-cathode fluorescent tube current is 4.5 mAr for lighting for 1 minute or more.
-3 including the case where control to lower to ms was performed
FIG. 13A shows the luminance rise characteristics at 0 ° C.

Fifth Embodiment As a fifth embodiment, in the structure of the second embodiment, the current of the cold cathode fluorescent tube having a small heat capacity and a high heat generation is shown in Table 9.
As shown in FIG. 13 and FIG. 13 (b), the cold cathode fluorescent lamp current is set at a slightly larger value of 6.0 mArms within one minute after the start of lighting, and the cold cathode fluorescent lamp current is set at 4.5. mAr
minus 3 when the control to decrease the current value to ms is performed.
FIG. 13A shows the luminance rise characteristics at 0 ° C.

Example 6 As Example 6, the current of the cold cathode fluorescent tube having a small heat capacity and a high heat generation in the structure of Example 3 is shown in Table 9.
As shown in FIG. 13 (b), the current of the cold cathode fluorescent lamp is set slightly higher at 6.0 mArms within one minute of the start of lighting, and the current of the cold cathode fluorescent lamp is set at 4.5 mArms for one minute or more of lighting.
-30 when the control to decrease to s is performed
FIG. 13A shows the luminance rise characteristics at a temperature of ° C.

(Comparative Example 1) As Comparative Example 1, a cold cathode fluorescent tube conventionally used was installed in an illuminating device having the structure shown in FIG.
As shown in (b), the rated current is 7.0 mA for one minute from the start of lighting.
-3 which is 9.0 mArms, which is larger than rms, and returns to the rated 7.0 mArms after lighting for 1 minute or more.
FIG. 13A shows the luminance rise characteristics at 0 ° C.

(Comparative Example 2) As Comparative Example 2, a cold cathode fluorescent tube conventionally used was installed in an illuminating device having the structure shown in FIG. Attached to. As shown in Table 9 and FIGS. 13B and 13C, the cold cathode fluorescent lamp current was 7.0 mArm.
s, and the power supplied to the heater was fixed at 5 W. FIG. 13A shows the luminance rise characteristics at −30 ° C. in this case.

From the results of the luminance rise characteristics in each case of FIG. 13A, it can be seen that the embodiment of the present invention has significantly improved luminance rise as compared with the prior art.
Further, in Examples 4 to 6 of the present invention, even when a boost current is supplied, the fluctuation of the luminance is within -25%, and the luminance rising characteristics are very stable. Here, the luminance fluctuation refers to a rate of a luminance decrease that occurs when switching from the boost current to the rated current. This luminance variation is given by {(Bn / Bb) -1} · 100 (%). Here, Bn is the luminance at the time of switching the rated current, Bb
Is the luminance at the end of the boost.

[0083]

[Table 9] Lamp current after lighting (tube current) Presence / absence of selective polarizing reflection sheet (mArms) Up to 1 minute 1 minute or more Linear polarization type Circular polarization type Example 1 4.5 4.5 None None Example 2 4.5 4.5 Yes No Example 3 4.5 4.5 No Yes Example 4 6.0 4.5 No No Example 5 6.0 4.5 Yes No Example 6 6.0 4.5 No Yes Comparative Example 1 9 0.0 7.0 --- --- Comparative Example 2 7.0 7.0 --- ---

[0084]

As described in the above embodiments, the display device using the illumination device provided with the small heat capacity and high heat generation type cold cathode fluorescent tube of the present invention and the selective polarization reflection sheet has a heater whose brightness rises at low temperature. It was better than the one equipped, and solved the problem of initial brightness rise at low temperature, which was the original purpose. The advantage of the solution of the present invention is that it does not use a heater and thus is excellent in terms of safety. Further, since a heater-related circuit is not required, a significant cost reduction can be achieved. Also, there is no need to assemble the heater. In addition, when a cold cathode fluorescent tube is heated using a heater, heat energy is applied indirectly to the components other than the cold cathode fluorescent tube of the lighting device, which leads to unnecessary temperature rise of the lighting device due to conduction or radiation. However, in the case of a cold cathode fluorescent tube having a small heat capacity and a high heat generation, heat energy can be directly supplied to the inside of the cold cathode fluorescent tube to which heat energy is to be applied, and power can be saved because a heater is not used. Furthermore, since the periphery of the cold cathode fluorescent tube having a small heat capacity and a high heat generation is blocked by an air layer, there is an advantage that unnecessary temperature rise of the lighting device is suppressed. The low-heat-capacity, high-heat-type cold-cathode fluorescent tubes have a low-temperature luminance rise at the time of using a conventional heater, and a short time after the start of lighting, luminance saturation occurs. Small fluctuations in brightness. Next, compared with the case where the cold cathode fluorescent lamp current is excessively supplied at the initial stage of lighting without using a heater, the present invention can make the cold cathode fluorescent lamp current smaller than that of the conventional one, so that power saving and cooling can be achieved. It is possible to extend the life of the cathode fluorescent tube. Further, the luminance rising characteristic at a low temperature, which is the original purpose, is much better than that in a case where the cold cathode fluorescent lamp current is excessively supplied at the initial stage of lighting.

[Brief description of the drawings]

FIG. 1 shows a display device 100 and a lighting device 110 according to the present invention.
FIG. (A) is a schematic diagram of the display device 100, and (b) is a 1B-1B cross-sectional view of a lighting device 110 included in the display device 100.

FIG. 2 is a graph showing a lighting start ambient temperature dependency of a luminance rising time constant of the present invention and a conventional example.

FIG. 3 is a graph showing a lighting start ambient temperature dependency of a factor before exponent of a luminance rise characteristic of the present invention and a conventional example.

FIG. 4 is an Arrhenius plot showing a lighting start ambient temperature dependency of a factor before exponent of a luminance rise characteristic of the present invention and a conventional example.

FIG. 5 is a graph showing a luminance rising characteristic of the cold cathode fluorescent tube according to the present invention.

FIG. 6 is a graph showing a luminance rising characteristic of a conventional cold cathode fluorescent tube.

FIG. 7 is a graph showing a fluorescent tube current dependency of a calorific value per unit length of the cold cathode fluorescent tubes of the present invention and a conventional example.

FIG. 8 is a graph showing the dependence of the calorific value per unit volume of the cold cathode fluorescent tubes of the present invention and the conventional example on the fluorescent tube current.

FIG. 9 is a graph showing a relationship between a fluorescent tube current and a fluorescent tube voltage in the cold cathode fluorescent tubes of the present invention and the conventional example.

FIG. 10 is a graph showing the relationship between the fluorescent lamp current and the fluorescent lamp power consumption voltage in the cold cathode fluorescent tubes of the present invention and the conventional example.

FIG. 11 is a block diagram showing a control circuit system of the lighting device of the present invention.

FIG. 12 is a flowchart illustrating a driving method of the lighting device of the present invention.

FIG. 13 is a diagram showing luminance rising characteristics and driving conditions of cold cathode fluorescent tubes according to an example of the present invention and a comparative example.
(A) is a luminance rise characteristic of the example and the comparative example, (b)
Represents the tube current in the example and the comparative example, and (c) represents the power supplied to the heater used in the comparative example 2, respectively.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Small heat capacity high heat generation type cold cathode fluorescent tube 2 Reflection sheet 3 Light guide 4 Diffusion sheet 5 Lens sheet 6 Selective polarization reflection sheet 7 Diffusion sheet 8 Display element 100 Display device 110 Illumination device

Claims (14)

[Claims] 1. Unit length (1 cm) of a glass tube of a fluorescent part
A lighting device having a cold cathode fluorescent tube having a heat capacity per unit of 0.035 Wsec / ° C. or less. 2. The heat capacity (Wsec / ° C.) per unit length (1 cm) of the glass tube of the fluorescent portion of the cold cathode fluorescent tube.
The structure factor time constant τs given by the product of C and the thermal resistance (° C./W)R is 11 seconds or less, and R = (Ts−T) /
{(Vccft−Vp) · Iccft / L}, and V
ccft is a fluorescent tube voltage (Vrms), Vp is a fluorescent tube electrode voltage drop (Vrms), and Iccft is a fluorescent tube current (Ar
ms), L is the length (cm) of the fluorescent tube, T is the ambient temperature (° C.), Ts is the wall temperature of the saturated tube (° C.). The lighting device according to claim 1, wherein the temperature of the wall is a temperature when the wall reaches a steady state. 3. The cold-cathode fluorescent tube has a glass tube cross-sectional area of D
t (mm ² ), the sealed gas cross-sectional area is Dg (mm ² ), and the inner diameter of the glass tube is da (mm ² ): Dt / Dg <2 /
The lighting device according to claim 1, wherein the lighting device satisfies a relational expression of da. 4. A calorific value Wv (W) per unit volume (1 cm ³ ) of a glass tube of a fluorescent portion of the cold cathode fluorescent tube and a fluorescent tube current Iccft (mArms) are Wv / Ic.
The lighting device according to claim 1, wherein a relationship of cft ≧ 0.5 is satisfied. 5. The time constant τ at which the luminance of the cold cathode fluorescent lamp rises from −10 ° C. of the lighting start ambient temperature T (° C.) to + 10 ° C.
In the range of 25 ° C., τ ≦ −0.0006T ³ +0.
The lighting device according to claim 1, wherein the lighting device satisfies a relationship of 0288T ² −0.4668T + 26.8. 6. The exponential factor A (percentage of the saturated relative luminance to the exponential factor A0) of the luminance rise characteristic of the cold cathode fluorescent tube is: A ≧ A ≧
The lighting device according to claim 5, wherein a relationship of 0.92T + 60 is satisfied. 7. The lighting device according to claim 6, wherein the activation energy of the cold-cathode fluorescent tube in the ambient temperature range of the lighting start of the pre-exponential factor is 3.0 kcal / mol or less. 8. The cold cathode fluorescent tube according to claim 1, wherein 95% or more of the total surface area of the fluorescent portion is in contact with air, and 50% or more of the light from the cold cathode fluorescent tube is used for illumination. The lighting device according to any one of claims 7 to 10. 9. The lighting device according to claim 1, further comprising a selective polarizing sheet on a light emission side of the cold cathode fluorescent tube. 10. The illuminating device according to claim 1, wherein a lamp current of a constant value is supplied to the cold cathode fluorescent tube in an operating state. 11. A lighting device further comprising: a temperature detector for detecting an ambient temperature of the cold cathode fluorescent tube; and a computing device for setting a predetermined tube current based on the temperature detected by the temperature detector. The lighting device according to claim 1, wherein a tube current supplied to the cold cathode fluorescent tube is controlled based on an ambient temperature. 12. A temperature detecting step of detecting an ambient temperature of the cold cathode fluorescent tube, and a step of setting a predetermined tube current based on the temperature detected by the temperature detector,
The method according to any one of claims 1 to 9, further comprising the step of controlling a tube current supplied to the cold-cathode fluorescent tube based on a lighting start ambient temperature. 13. A display device comprising: the lighting device according to claim 1; and a transmissive display element that receives light from the lighting device. 14. The display device according to claim 13, wherein the transmissive display element is a liquid crystal display element.