Answer: F. 30-60°.
Answer analysis: When discussing the luminous angle of LED direct plug round head lamp beads, we must first understand how the luminous angle is defined. The luminous angle refers to the distribution range of the light emitted by the LED lamp bead on a specific plane, usually measured in angles. For different types of LED lamp beads, the luminous angle will be different, depending on factors such as the design of the lamp bead, the packaging method, and the shape of the lens or reflector cup.
Now, let's analyze the given options one by one:
A: 15-20°: This range usually corresponds to some high-brightness and highly concentrated LED lamp beads, such as some special-purpose spotlights or indicator lights. However, it is not generally applicable to LED direct plug round head lamp beads.
B: 90°: Although the luminous angle of some LED lamp beads may be close to 90°, this option is relatively single and not comprehensive, and may not accurately reflect the common luminous angle of LED direct plug round head lamp beads.
C: 90-120°: This range covers a wider luminous angle and is applicable to a variety of LED lamp beads, including some direct plug LEDs. However, for straight plug-in round-head lamp beads, it may tend to have a larger luminous angle range, but it may not be completely accurate.
D: 120°: Although the luminous angle of some LED lamp beads may reach or approach 120°, this single value is also not comprehensive and may not be the most common luminous angle of straight plug-in round-head lamp beads.
E: 120-140°: This range covers a wider luminous angle, but it is usually not a typical luminous angle for straight plug-in round-head lamp beads. This large-angle luminous range may be more suitable for some specially designed LED lamp beads.
F: 30-60°: This range is relatively moderate and conforms to the luminous characteristics of many LED straight plug-in round-head lamp beads. Lamp beads with this angle have both a certain degree of focusing and a certain range of light distribution, which is suitable for a variety of lighting and indication applications.
Taking the above factors into consideration, the luminous angle of LED straight plug-in round-head lamp beads is usually within a relatively moderate range, so that good lighting effects can be provided in various applications. Therefore, option F (30-60°) best matches the common luminous angle range of LED direct plug round head lamp beads.
Therefore, the correct answer is F: 30-60°.