Graphic analysis: four typical LED light distribution curves

The first type: rectangular LED

It is mainly used as an indicator light on appliances or meters, and its luminous intensity is very low. Figure 2 is a light distribution curve of a green LED with a 45° spacing between each other. Although their shapes are quite different, the normal illuminances are equal, 216 mcd, because it can be seen from the figure that the shape of the light distribution curve near the normal direction is the same. Imagine if there is no 8 light distribution curve as shown in the figure, the normal luminous intensity value will be mistaken for a good tube.

Second: oval LED

This is a product that has only recently appeared, mainly for display screens. Because the viewing angle of the display requires a large left and right, but the upper and lower are small, so as to suit the visual characteristics of people. Therefore, the long-axis field of view of the elliptical LED is large, and the short-axis field of view is small, as shown in Figures 3 (a) and (b). The mounting position on the display is that the long axis of the tube is horizontal and the short axis is vertical.

The third type: special LED for traffic lights

Although the road traffic lights are divided into three types: red, green and yellow, their shape of the light distribution curve is shown in Figure 4. Unlike other LEDs, its light distribution curve is one-sided and has a serious asymmetry. This makes sense because the traffic lights are viewed by motorists, cyclists or passers-by, and the eyes are much lower than the traffic lights. If ordinary monochrome LEDs are used, the light shining on the sky is useless. , causing a great waste of electrical energy.

Fourth: Monochromatic LED

The distribution curve of a considerable proportion of monochromatic LEDs is shown in Fig. 5, that is, the distribution of luminous intensity is small and small around the periphery. If you use a piece of white paper, it will show an image with a bright circle around and a dark spot in the middle. The initial explanation is shown in Figure 6. On the one hand, because the shape of the LED is equivalent to the presence of a lens, it is not an ideal lens. On the other hand, although the cross-sectional area of ​​the chip of a common LED is only 011 to 0125 mm2, the angle of view of the light emitted by the chip is still large relative to the lens, so the chip cannot be regarded as a point source. The light from different fields of view converges on a circle near point A and then diffuses out, causing the light spots near the far field to appear bright and dark.

Edit: Sophy