The fresnel lens is a thin sheet made of plastic material. One side of the lens surface is smooth, and the other side is molded with concentric circles from small to large. Its grooves is designed from the interference of light, the relative sensitivity, and receiving angle requirements.
Compared to the conventional Spherical Lens, a Fresnel lens by the lens divided into a series of concentric circles theoretically infinite number of lines (i.e., the Fresnel zone) to achieve the same optical effect, while saving the amount of material For these lines, the overall thickness of the lens is reduced; ordinary Fresnel convex lens is actually a continuous curved surface is truncated to a section of a discontinuous change of the curvature as the surface is finely divided, so look like a
Fresnel lenses are mainly used in optical imaging industry ( projectors, VR, AR, etc.), Fresnel lenses are used in LED lighting distribution (spotlights, floodlights, stage lights, traffic signal lights), infrared induction lenses are used in ( industry 4.0 intelligent fields, building security systems, induction lighting, etc.), large Fresnel lenses are used in ( photovoltaic concentrated light generation, heat collection, light utilization, etc.).
Fresnel Lens,Fresnel Lenses, Led Fresnel Light,Linear Fresnel Lenses,Fresnel Spotlight Changchun Realpoo Photoelectric Co., Ltd. , https://www.optics-realpoo.com Figure 19.14 is the circuit for measuring the resistance RX. When W1 or W2 is changed, the voltage of pin 6 of 555 is equal to or higher than two-thirds of the power supply voltage of 6V, C1 is continuously charged and discharged, and the voltage on C1 fluctuates up and down in the third of the power supply voltage of 6V. Shock, LED1 and LED2 will flash alternately. When the voltage of pin 6 of 555 is lower than two-thirds of 6V, C1 will not discharge. Only charging, the voltage on C1 will be charged to 6V, and the output of 555 is always high. Therefore, LED1 is off and LED2 is always on. . According to the above working principle, it can be used to measure RX.
The switch K selects the range, the range is 5kΩ when K is turned on A, and the range is 500kΩ when K is turned on. The measured resistance is actually half the value of W1 or W2. According to this range, W1 and W2 are scaled, and the indicated value of W1 and W2 (that is, one-half of the actual resistance) is the RX value.
The measurement method is as follows: connect the measured resistor, select the range, adjust W1 or W2, observe the LED1 and LED2 illumination status, and make the two LEDs change from alternating flash (higher flicker frequency, it is difficult to detect flashing) LED1 is extinguished and LED2 is illuminated. At this time, the indicated value of W1 or W2 is the resistance of the resistor RX under test. 
circle around the lines. Fresnel lenses may in fact be regarded as a series of prisms are arranged in a ring, wherein the relatively sharp edge, and the center of the convex surface is relatively smooth.
