The luminous intensity of an LED is a characterization of its luminous intensity in a certain direction. Since the luminous intensity of the LED differs greatly in different spatial angles, it is necessary to study the luminous intensity distribution characteristics of the LED. This parameter is of great practical significance and directly affects the secondary light distribution design of the LED.
(1) Luminous intensity (normal light intensity) is an important performance characterizing the luminous intensity of light-emitting devices. The LED is packaged in a cylindrical and spherical shape. Due to the action of the convex lens, it has strong directivity: the light intensity in the normal direction is the largest, and the angle of intersection with the horizontal plane is 90°. When deviating from the normal direction by a different angle θ, the light intensity also changes.
(2) Luminous intensity distribution. A temperature map of the luminescence distribution of GaAsP-LED generated on a GaP substrate, as shown in Figure 1, the spectral line width is 400, and the emission angle width is about 22°. The radiant flux of the LED is concentrated and emitted within a certain angle.
The luminous intensity of an LED is a characterization of its luminous intensity in a certain direction. Since the luminous intensity of the LED differs greatly in different spatial angles, it is necessary to study the luminous intensity distribution characteristics of the LED. This parameter is of great practical significance and directly affects the secondary light distribution design of the LED.
(1) Luminous intensity (normal light intensity) is an important performance characterizing the luminous intensity of light-emitting devices. The LED is packaged in a cylindrical and spherical shape. Due to the action of the convex lens, it has strong directivity: the light intensity in the normal direction is the largest, and the angle of intersection with the horizontal plane is 90°. When deviating from the normal direction by a different angle θ, the light intensity also changes.
(2) Luminous intensity distribution. A temperature map of the luminescence distribution of GaAsP-LED generated on a GaP substrate, as shown in Figure 1, the spectral line width is 400, and the emission angle width is about 22°. The radiant flux of the LED is concentrated and emitted within a certain angle.
(3) The degree of light output. Figure 2 shows the relationship between the light output of several semiconductor PN junctions and the input current. It can be seen that GaAs1-xPx and Gal-xAlxAs-LED have good linearity, while the other two are quite poor.
(3) The degree of light output. Figure 2 shows the relationship between the light output of several semiconductor PN junctions and the input current. It can be seen that GaAs1-xPx and Gal-xAlxAs-LED have good linearity, while the other two are quite poor.
(4) Angular distribution of luminous intensity. The angular distribution of luminous intensity describes the light intensity distribution of the LED luminescence in all directions in space. It mainly depends on the packaging process (including the bracket, die head, and whether to add scattering agent to the epoxy resin). In order to obtain the angular distribution of high directivity shown in Figure 3, the following measures should be taken: the LED chip position should be farther away from the die head. Use a cone-shaped (bullet) die head. Do not add a scattering agent in the epoxy resin encapsulating the LED.
(4) Angular distribution of luminous intensity. The angular distribution of luminous intensity describes the light intensity distribution of the LED luminescence in all directions in space. It mainly depends on the packaging process (including the bracket, die head, and whether to add scattering agent to the epoxy resin). In order to obtain the angular distribution of high directivity shown in Figure 3, the following measures should be taken: the LED chip position should be farther away from the die head. Use a cone-shaped (bullet) die head. Do not add a scattering agent in the epoxy resin encapsulating the LED.
Taking the above measures can make the LED scattering angle 2θ1/2=6°, which greatly improves the directivity. The current scattering angles (2θ1/2) of several commonly used round LED packages are: 5°, 10°, 30°, and 45°.
For the electrical characteristics of LEDs and the luminous efficiency of LEDs, please refer to previous articles.