How to identify photosensitive and infrared emission tubes without a Multimeter

Observe in the same lighting environment and record the following three points: 1. the infrared emission diode is visible in the right side of the lens. It has a shape similar to a small cross, and the photosensitive diode is a single point and there is a point on the positive pole; 2. The sensitivity of the infrared receiver and receiver is different, and the sensitivity of the photosensitive receiver is higher; 3. The most important point is that, similar to this type of components, the pin must be the same as the head and tail. No, it is obviously prominent on the top of the pin. In practice, I have come to the conclusion that, most of them may be defective, and the sensitivity is basically zero. The nice thing to say is that "the anti-interference capability is strong, so that all signals that should be accepted are blocked ". This is a heavy lesson for our team, because such devices directly affect the implementation of light-seeking and other functions.