Light guide film, backlight module and display device having the same

A light guide film which is adapted for use with a light source has a light transmissive substrate and a light-transmissive member unit. The substrate has a light-exiting top surface, a bottom surface that is opposite to the top surface and a lateral surface that interconnects the top and bottom surfaces and that is adapted to face toward the light source. The member unit includes a bottom member that is disposed on the bottom surface of the substrate, and a lateral member that is connected to the lateral surface of the substrate and that is adapted to be disposed between the light source and the lateral surface of the substrate. The substrate has a refractive index which is less than that of the member unit.

FIELD

The disclosure relates to an optical element, more particularly to a light guide film, a backlight module having the same, and a display device having the same.

BACKGROUND

Referring toFIG. 1, a conventional light guide film1is adapted for use with a light source2for guiding light emitted therefrom. When the light emitted from the light source2enters the conventional light guide film1, it will propagate within the conventional light guide film1by total internal reflection. However, since the conventional light guide film1is relatively thin comparing to the size of the light source2, part of the light emitted from the light source2will not enter the conventional light guide film1and result in energy loss.

SUMMARY

Certain embodiments of the present disclosure provide a light guide film that may alleviate the aforementioned drawbacks of the prior art. Such a light guide film may be adapted for use with a light source and have a light-transmissive substrate and a light-transmissive member unit. The substrate has a light-exiting top surface, a bottom surface that is opposite to the top surface, and a lateral surface that interconnects the top and bottom surfaces and that is adapted to face toward the light source. The plastic member unit may include a bottom member that is disposed on the bottom surface of the substrate, and a lateral member that is connected to the lateral surface of the substrate and that is adapted to be disposed between the light source and the lateral surface of the substrate. The substrate may have a refractive index which is less than that of the member unit.

DETAILED DESCRIPTION

Referring toFIG. 2, the first exemplary embodiment of a light guide film3according to the present disclosure, which is adapted for use with a light source4, includes a light-transmissive substrate31and a light-transmissive member unit32.

The substrate31of this embodiment has a light-exiting top surface312, a bottom surface313that is opposite to the top surface312, and a lateral surface311that interconnects the top and bottom surfaces312,313and that is adapted to face toward the light source4. As illustrated inFIG. 2, the lateral surface311of the substrate31is perpendicular to the bottom surface313of the substrate31in this embodiment. The substrate31may be made of a polymeric material, such as polycarbonate (PC) or polymethylmethacrylate (PMMA).

The member unit32of this embodiment includes a bottom member321that is disposed on the bottom surface313of the substrate31, and a lateral member322that is connected to the lateral surface311of the substrate31and that is adapted to be disposed between the light source4and the lateral surface313of the substrate31. In certain embodiments, the member unit32may be made from a UV-curable acrylate resin. In such embodiments, the member unit32may be formed by applying the UV-curable acrylate resin onto the substrate31, placing a light-transmissible mold onto the UV-curable acrylate resin applied on the substrate31, and curing the same with UV light. The bottom member321and the lateral member322may be integrally formed as one piece as illustrated inFIG. 2.

As shown inFIG. 2, the lateral member322of this embodiment is tapered toward the lateral surface311of the substrate31and has a light-incident lateral surface324that is adapted to face toward the light source4, a connecting surface325that is opposite to the lateral surface324and that abuts against the lateral surface311of the substrate31, and a top surface323that extends obliquely to meet with the top surface312of the substrate31.

The substrate31may have a refractive index (n1) which is less than a refractive index (n2) of the member unit32. As illustrated inFIG. 2, when part of the light emitted from the light source4and incident into the light guide film3via the lateral surface324of the lateral member32, it is desired to have total internal reflection occur at the top surface323of the lateral member322for reducing energy loss as light is transmitted through the light guide film3. Since the refractive index (n2) of the member unit32is larger than the refractive index (n1) of the substrate31in this embodiment, there is a higher chance to have total internal reflection occur at the top surface323of the lateral member322and the bottom surface326of the bottom member321, so as to effectively reduce energy loss of the light guide film3. In certain embodiments, a ratio (n2/n1) of the refractive index (n2) of the member unit32to the refractive index (n1) of the substrate31may be greater than 1 and less than or equal to 1.5, i.e., 1<(n2/n1)≤1.5. Examples (A) to (G) inFIG. 3shows the relationship between the ratio (n2/n1) and the energy loss during the light transmission within the light guide film3observed from an observation point5. Examples (A) to (G) respectively have the ratios (n2/n1) of 1.0(1.59/1.59), 0.9 (1.49/1.59), 1.06 (1.69/1.59), 1.13 (1.80/1.59), 1.26 (2.00/1.59), 1.38 (2.20/1.59) and 1.51 (2.40/1.59), and the energy loss of each Example represented inFIG. 3is scaled by being divided by the energy loss value obtained from Example 1. It is clearly shown that the observed energy loss varies as the ratio (n2/n1) varies. When the ratio (n2/n1) is greater than 1, e.g., Examples (C) to (G), the energy loss of the light guide film3is lower than that observed from Example 1, with the ratio being equal to 1. As the ratio (n2/n1) increases and approaches 1.5, the energy loss of the light guide film3decreases accordingly. On the other hand, when the ratio is smaller than 1, e.g., Example (B), the energy loss is greater than that observed from Example (A).

Referring toFIG. 4, the second exemplary embodiment of the light guide film3according to the present disclosure is shown to be similar to that of the first exemplary embodiment, with the differences residing as follows. As illustrated inFIG. 4, the bottom member321of the second exemplary embodiment has a bottom surface326that is opposite to the substrate31and that is formed with a plurality of microstructures327. Each of the microstructures327may be configured as a protruding dot as illustrated inFIG. 4, but is not limited thereto according to the present disclosure. Total internal reflection may be hindered at the microstructures327on the bottom surface326of the bottom member321due to the varied incident angles, thereby allowing the light that propagates within the light guide film3to exit from the top surface312of the substrate31. In certain embodiments, the microstructures327may have a surface density that is negatively correlated with a distance to the lateral member322as illustrated inFIG. 4, so as to increase the amount of light exiting from the top surface312at locations away from the light source4.

Referring toFIG. 5, the third exemplary embodiment of the light guide film3according to the present disclosure is shown to be similar to that of the first exemplary embodiment, with the difference residing in that the top surface323of the lateral member322meets with the top surface312of the substrate31in a co-planar manner. The light guide film3of the third exemplary embodiment has advantages similar to those of the first exemplary embodiment.

Referring toFIG. 6, the fourth exemplary embodiment of the light guide film3according to the present disclosure is shown to be similar to that of the first exemplary embodiment, with the difference residing in that the lateral member32and the bottom member31are configured as separate pieces which are not connected as illustrated inFIG. 6. The light guide film3of the fourth exemplary embodiment has advantages similar to those of the first exemplary embodiment.

Referring back toFIGS. 2 and 4 to 6, an exemplary embodiment of a backlight module according to the present disclosure may include the light source4, and the aforesaid light guide film3as illustrated in either one ofFIGS. 2, 4, 5 and 6for guiding the light emitted from the light source4toward a direction and exited from the top surface312of the substrate31. In certain embodiments, the lateral member322of the light guide film3may have an overall thickness that is not less than that of the light source4, so as to ensure the light emitted from the light source4is substantially incident into the light guide film3via the light-incident lateral surface324of the lateral member32. In certain embodiments, the substrate31may have a thickness that is less than that of the light source4.

As illustrated inFIG. 7, one exemplary embodiment of a display device according to the present disclosure may include the backlight module, for instance, one as illustrated inFIG. 10, and a display panel6that is disposed to face the top surface312of the substrate31, so as to receive the light exit from the top surface312of the light guide film3of the backlight module.

In summary, by virtue of the member unit32having desirable refractive index and by virtue of the configuration of the lateral member322, the energy loss of the light guide film3according to the present disclosure can be effectively reduced.

Reference in the specification to “one embodiment,” “an embodiment,” “a first embodiment,” “a second embodiment” and so forth means that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least an implementation. The appearances of the phrase “in one embodiment,” “in this embodiment”, “in the embodiment” in various places in the specification may or may not be all referring to the same embodiment. Various features, aspects, and exemplary embodiment(s) have been described herein. While various features and aspects may have been described with reference to different drawings depicting varying specific embodiments, the features, aspects, and exemplary embodiment(s) are susceptible to combination with one another as well as to variation and modification, as will be understood by those having ordinary skill in the art.

This disclosure is not limited to the disclosed exemplary embodiment(s) but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.