While running towards traffic early morning before sunrise I recently noticed that the new automobile LED (white) lights when viewed at a distance appear blueish, but when the light is viewed much closer it appears white.

So I tried researching on line to see if I could find an explanation including this LED wiki which gives a fairly detailed description of the technology. But there doesn't seem to be anything close to explaining what I've observed. The references do explain at least two methods of producing the white light including one in which red, blue and green LED sources are 'mixed' together.

So I'm guessing that it might be some kind of process of dispersion where some of the red and green are attenuated at distance, over the blue component and so the light appears blueish. Or is there some other optical effect? Rather in my eye than the atmosphere?

There is maybe another possibility. In my far field observation (hundreds of feet) I'm closer to the axis of the light beam. Whereas in my near field observation (10 to 20 ft) I'm off maybe 60 degrees or more from the beam axis. So maybe a color indifference as a function of angle?

  • $\begingroup$ If the white LED features a blue LED pumping a phosphor (which emits the green and red contribution), it’s possible that on axis will contain more blue light than off axis observation because you are in direct line with the blue LED emission direction. $\endgroup$ – boyfarrell Mar 20 '18 at 1:52
  • $\begingroup$ Or just brightness, you might not be able to determine the color of a very bright close light $\endgroup$ – Martin Beckett Mar 20 '18 at 2:04

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