Cold cathode fluorescent lamp and backlight module using same

A cold cathode fluorescent lamp includes: a working gas, a transparent tube, a fluorescent layer, an anode, a cold cathode and a light cut filter film. The transparent tube receives a working gas, and has an inner surface and an outer surface. The fluorescent layer is formed on the inner surface of the transparent tube. The light cut filter film is formed on the outer surface of the transparent tube. The cold cathode is disposed at one end of the transparent tube and the anode is disposed at the other end of the transparent tube. The cold cathode fluorescent lamp can block most part of the ultraviolet lights and infrared lights to irradiate at the light guide plate, whereby the light guide plate has a long service life without following problems such as thermal deformation, deflection, turn color and transformation.

FIELD OF THE INVENTION

The present invention relates to cold cathode fluorescent lamp and backlight module, particularly, to a cold cathode fluorescent lamp and backlight module for use in, e.g., a liquid crystal display (LCD).

DESCRIPTION OF RELATED ART

In a liquid crystal display device, liquid crystal is a substance that does not itself radiate light. Instead, the liquid crystal relies on receiving light from a light source, thereby displaying images and data. In the case of a typical liquid crystal display device, a backlight module powered by electricity supplies the needed light.

Conventional light sources used in the backlight modules generally include light emitting diodes (LEDs), and cold cathode fluorescent lamps (CCFLs). However, the LED has a shortcoming of low luminous efficiency and is often used in small size liquid crystal displays such as cell phone, personal data assist (PDA) and so on.

Referring toFIG. 1(Prior art), a conventional CCFL100is shown. The CCFL100includes a transparent tube110, a cold cathode134, an anode132, and a fluorescent layer140. The fluorescent layer140is formed on an inner surface of the transparent tube110. The cold cathode134and the anode132are respectively disposed at the two ends of transparent tube110and are respectively electrically connected to an exterior power source (no shown). The transparent tube110is filled with mercury vapor120and an inert gas150.

When the power source supplys a current to the cold cathode134and the anode132, an electric field therebetween is produced. Electrons are emitted from the cold cathode134. The electrons are accelerated by the electric field and then collide with gaseous molecules of the mercury vapor and the inert gas. This causes excitation of the mercury vapor and subsequent remission. The remission process causes radiation of ultraviolet rays. The ultraviolet rays irradiate a fluorescent material of the fluorescent layer140, whereby a part of the ultraviolet rays are converted into visible light and infrared light which produces a great deal of heat energy.

A conventional backlight module generally includes a light guide plate and a light source. When the CCFL100is used as a light source in the backlight module, the CCFL100is disposed adjacent a light guide plate of the backlight module. Infrared light and a part of ultraviolet light emitted from the CCFL100irradiate the light guide plate directly. Because the light guide plate is usually formed of transparent synthetic resin material, such as polymethyl methacrylate (PMMA) and polycarbonate (PC), the light guide plate has thermal deformation and deflection problems by absorbing a great deal of heat energy produced by the infrared light, and may have turn color and transformation problems due to long-term irradiation by the ultraviolet light. It caused serious problems on illuminance uniformity, poor brightness, and worse optical performance of the backlight module of the LCD.

What is needed, therefore, is a cold cathode fluorescent lamp which can reduce the emission of ultraviolet light and infrared light.

SUMMARY OF INVENTION

A CCFL according to a preferred embodiment includes a working gas; a transparent tube receiving the working gas therein, the transparent tube having an inner surface and an outer surface; a fluorescent layer formed on the inner surface of the transparent tube; a cold cathode disposed at one end of the transparent tube; an anode disposed at the other end of the transparent tube; and a filter film formed on the outer surface of the transparent tube.

A backlight module according to a preferred embodiment includes a light guide plate and a CCFL. The light guide plate includes an incident surface. The CCFL is disposed adjacent the incident surface of the light guide plate. The same CCFL as described in the previous paragraph is employed in this embodiment.

DETAILED DESCRIPTION

Reference will now be made to the drawings to describe preferred embodiments of the present invention in detail.

Referring toFIG. 2, a CCFL200, in accordance with a first embodiment, is shown. The CCFL200includes a transparent tube210, a fluorescent layer220, an anode232, a cold cathode234, and a light cut filter film260. The transparent tube210is sealed in a form of cylinder and filled with a working gas240. The transparent tube210has an inner surface and an outer surface. The fluorescent layer220is formed on the inner surface of the transparent tube210. The light cut filter film260is deposited on the outer surface of the transparent tube210. The cold cathode234is disposed at one end of the transparent tube210and the anode232is disposed at the other end of the transparent tube210. The cold cathode234and the anode232can be respectively electrically connected to an external power source (not shown).

It is to be understood that the shape of the transparent tube210could also be in a form of prism or other similar shapes. A material of the transparent tube can be selected from a group comprising of glass, transparent resin material. In the illustrated embodiment, the light cut filter film260is an ultraviolet and infrared light cut filter film (UV-IR light cut filter film) that can block the ultraviolet light and infrared light from passing through the CCFL200. The working gas240is a mixture of xenon (Xe), argon (Ar) and neon (Ne) gases.

Referring toFIG. 3, the UV-IR light cut filter film has a stack structure. The stack structure comprises a plurality of high refractive index layers and a plurality of low refractive index layers. The stack structure can be defined as follows: 0.5(0.5HL0.5H)2×1.666(0.5LH0.5L)×1.4(0.5LH0.5L)6×1.6(0.5LH0.5L)×1.8(0.5LH0. 5L)8. Wherein, H represents a base thickness of a high refractive index layer which is equal to one fourth of a central wavelength (λ) associated with the filter film, L represents a base thickness of a low refractive index layer which is equal to one fourth of a central wavelength associated with the filter film, the expression enclosed in each parenthesis represents a filter cavity, and the superscript represents the number of repetition of the expression enclosed in that parenthesis. The numbers before the parenthesises represent thickness times for the respective filter cavities. For one example, 0.5(0.5HL0.5H)2represents two consecutive filter cavities269each consisting of two high refractive index layers261and a low refractive index layer262sandwiched between the high refractive index layers261. In each of the filter cavities269, each of the high refractive index layers261has a thickness equal to 0.5×(0.5×(¼)λ), and the low refractive index layer262has a thickness equal to 0.5×(¼)λ. For another example, 1.666(0.5LH0.5L) represents only one filter cavity268consisting of two low refractive index layers263and a high refractive index layer264sandwiched between the low refractive index layers263. In the filter cavity268, each of the low refractive index layers263has a thickness equal to 1.666×(0.5×(¼)λ), and the high refractive index layer264has a thickness equal to 1.666×(¼) λ.

The refractive index of the high refractive index layer is in an approximate range from 2.1 to 2.4. A material of the high refractive index layer can be selected from a group consisting of titanium dioxide (TiO2), titanium pentoxide (Ti2O5) and tantalum pentoxide (Ta2O5). The refractive index of the low refractive index layer is in an approximate range from 1.4 to 1.6. A material of the low refractive index layer can be selected from a group consisting of silicon dioxide (SiO2) and aluminium oxide (Al2O3). In the illustrated embodiment, the high refractive index layer is made of titanium pentoxide and the low refractive index layer is made of silicon dioxide.

When the CCFL200in use, the cold cathode234and the anode232are supplied with a voltage by an external power source (not shown). An electric field is established between the cold cathode234and the anode232. Electrons are emitted from the cold cathode234and accelerated by the electric field, and then collide with gaseous molecules of the working gas240. This causes excitation of the working gas240and subsequent remission. The remission process causes radiation of ultraviolet rays. The ultraviolet rays irradiate a fluorescent material of the fluorescent layer220, whereby a part of the ultraviolet rays are converted into visible lights and infrared lights. The ultraviolet lights and infrared lights can be effectively blocked by the UV-IR light cut filter film from emitting out of the CCFL200.

FIG. 4shows a graph of a transmitted spectrum of an UV-IR light cut filter film of the CCFL200ofFIG. 2, wherein TUV is a dividing point of the ultraviolet light area and the visible light area, and wherein TIR is a dividing point of the visible light area and the infrared light area. It shows that ultraviolet light transmittance associated with the UV-IR light cut filter film is below 2% and infrared light transmittance associated therewith is also below 2%. Therefore, most part of ultraviolet lights and infrared lights are blocked by the UV-IR light cut filter film from emitting out of the CCFL200.

It is to be understood that a light cut filter film of the present CCFL can also employs either ultraviolet light cut filter film or infrared light cut filter film. A preferred stack structure of the ultraviolet light cut filter film can be defined as follows: (HL)7×(0.76 LH0.76 L)6and a preferred stack structure of the infrared light cut filter film can be defined as follows: 5(HL)7×(1.3 LH1.3 L)9(HL)8.

Referring toFIG. 5, a backlight module500using the CCFL200, in accordance with a first preferred embodiment, is shown. The backlight module500includes a light guide plate510and a CCFL200. The light guide plate510includes an incident surface512; an emitting surface514adjoining the incident surface512; and a reflecting surface516opposite to the emitting surface514. The CCFL200is disposed adjacent the incident surface512of the light guide plate510. The overall shape of the light guide plate510may be configured to be flat or wedge-shaped. In the illustrated embodiment, the shape of the light guide plate510is wedge-shaped.

Because of the CCFL200blocking most part of the ultraviolet light and infrared light to irradiate at the light guide plate510, the light guide plate has a long service life without following problems such as thermal deformation, deflection, turn color and transformation. Therefore, the backlight module500using the CCFL200can improve optical uniformity, poor brightness, and worse optical performance. In addition, the present CCFL employs a mixture gas as a working gas to replace with a mercury vapor that is toxic to humans and environmentally unsafe, whereby the present CCFL is environment friendly.

Finally, while the present invention has been described with reference to particular embodiments, the description is illustrative of the invention and is not to be construed as limiting the invention. Therefore, various modifications can be made to the embodiments by those skilled in the art without departing from the true spirit and scope of the invention as defined by the appended claims.