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What about focusing each LED source separately?

by rocqua 6y ago

bleepblorp 6y ago
LED car headlights do use this principle; it does have some applications. However, the diameter of each LED optic would need to at least equal the diameter of the single optic used for a point source light. The result would be an enormous searchlight with a very broad beam. I can't find any solid information on the quantitative light output of the AN/TVS-3, but xenon arc lamps typically produce 30 lumens per watt. Therefore, the 20KW AN/TVS-3 should produce around 600,000 lumens. Readily available high-power LEDs are capable of 1700 lumens, so equaling the AN/TVS-3 would take--as a very rough ballpark that does not take into account the different light distribution between LEDs and discharge lamps--350 LEDs and optics. The AN/TVS-3 uses 30" optics, so those optics would also need to be at least 30" in diameter. 350 30" optics is a lot more like a wall of light than a searchlight. Aiming that many separate optics would also be a nightmare.
- MisterTea 6y ago
  > I can't find any solid information on the quantitative light output of the AN/TVS-3, but xenon arc lamps typically produce 30 lumens per watt https://en.wikipedia.org/wiki/Luminous_efficacy https://en.wikipedia.org/wiki/Luminous_efficacy What I'm not sure of is if the lumins/watt rating is given for the light output or the power input. The input power rating is 450 Amps * 200 Volts * 1.732 = 155880 electrical watts. That's nearly 7.75 times as much electrical power as light output. That makes sense since the peak efficiency is about 7.3 for a xenon arc lamp.
- rocqua 6y ago
  Why does the optic need the same diameter? For gathering all of the light, with a mirror at least, I think you could place a smaller optic closer to the light and still capture the same fraction of the light? I probably am missing something about optics though.
  - bleepblorp 6y ago
    The ability of an optical system (a lens, mirror, or combination) to collimate the output of a light source into a narrowly diverging beam is directly proportional to the diameter of the optical system's final element and inversely proportional to the size of the light source. Bigger optics = less beam divergence = more useful range. This is a function of the diffraction limit[0] and is a property of physics. If you want to match the beam divergence of a 30" optical system, you have to use 30" optics; there are no shortcuts. [0] https://www.edmundoptics.com/knowledge-center/application-notes/imaging/diffraction-limit/ https://www.edmundoptics.com/knowledge-center/application-no...
    - rocqua 6y ago
      I know that we can create very large virtual apertures for receiving signals by using arrays of many receivers. The basic diffraction physics presume a single source, so it isn't totally obvious that they generalize to a multi-source system. I can, however, imagine that a multi source system would require in-phase light sources to kind of mimic a phased-array receiver on the send side.

What about focusing each LED source separately?

by rocqua 6y ago

What about focusing each LED source separately?

LED car headlights do use this principle; it does have some applications. However, the diameter of each LED optic would need to at least equal the diameter of the single optic used for a point source light. The result would be an enormous searchlight with a very broad beam. I can't find any solid information on the quantitative light output of the AN/TVS-3, but xenon arc lamps typically produce 30 lumens per watt. Therefore, the 20KW AN/TVS-3 should produce around 600,000 lumens. Readily available high-power LEDs are capable of 1700 lumens, so equaling the AN/TVS-3 would take--as a very rough ballpark that does not take into account the different light distribution between LEDs and discharge lamps--350 LEDs and optics. The AN/TVS-3 uses 30" optics, so those optics would also need to be at least 30" in diameter. 350 30" optics is a lot more like a wall of light than a searchlight. Aiming that many separate optics would also be a nightmare.

MisterTea 6y ago
> I can't find any solid information on the quantitative light output of the AN/TVS-3, but xenon arc lamps typically produce 30 lumens per watt https://en.wikipedia.org/wiki/Luminous_efficacy https://en.wikipedia.org/wiki/Luminous_efficacy What I'm not sure of is if the lumins/watt rating is given for the light output or the power input. The input power rating is 450 Amps * 200 Volts * 1.732 = 155880 electrical watts. That's nearly 7.75 times as much electrical power as light output. That makes sense since the peak efficiency is about 7.3 for a xenon arc lamp.
rocqua 6y ago
Why does the optic need the same diameter? For gathering all of the light, with a mirror at least, I think you could place a smaller optic closer to the light and still capture the same fraction of the light? I probably am missing something about optics though.
- bleepblorp 6y ago
  The ability of an optical system (a lens, mirror, or combination) to collimate the output of a light source into a narrowly diverging beam is directly proportional to the diameter of the optical system's final element and inversely proportional to the size of the light source. Bigger optics = less beam divergence = more useful range. This is a function of the diffraction limit[0] and is a property of physics. If you want to match the beam divergence of a 30" optical system, you have to use 30" optics; there are no shortcuts. [0] https://www.edmundoptics.com/knowledge-center/application-notes/imaging/diffraction-limit/ https://www.edmundoptics.com/knowledge-center/application-no...
  - rocqua 6y ago
    I know that we can create very large virtual apertures for receiving signals by using arrays of many receivers. The basic diffraction physics presume a single source, so it isn't totally obvious that they generalize to a multi-source system. I can, however, imagine that a multi source system would require in-phase light sources to kind of mimic a phased-array receiver on the send side.