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• Spectrum of a "warm white" LED night light

  Joseph Eoff • 11/11/2025 at 17:22 • 0 comments

  Someone turned on a night light here in my room in the hospital.  This light is in a good position for examination with my bifocal prism.

  This is a low power LED bulb, though it looks rather bright in the photo.

  
  Through my bifocal prism,  I can see a full spectrum of light from it.  The range runs from violet, through blue, green, yellow, and orange down to red.  Blue and violet are rather weak, as is the red - but at least there is some red there.  Yellow and green are rather stronger than in the "cool white" light in the examination room.  There is no gap in the green in this night light like there was in the "cool white" light.

  I tried again to make pictures with my phone.  

  No go.  At least part of the problem is the automatic white point adjustment.  Another is the automatic exposure.  Finally comes the difficulty of holding the phone and the glasses in a position to generate the spectrum while still being able to hit the "shutter" field on the phone.

  Sometimes it just takes telling some one about a problem to make you think of solutions.

  Phone cameras are capable of a bit more than making simple snapshots.  You can take things off of automatic and adjust them your self.

  I set the white point manually to "incandescent" then turned the exposure down as far as the camera allowed, et voilà:

  It took a bit of fiddling to line up the camera, the glasses, and the light source while also getting the camera far enough from the bifocal for it to focus - and all the while make sure that you've got a finger free that can tap the spot on the screen where the spectrum is.  

  That ain't no great shakes, but not bad for just using what you had on you when you landed in a hospital room with a broken foot.

  It does look a bit better "in person" through my eye instead of the camera.
  
  

• Being myopic helps

  Joseph Eoff • 11/09/2025 at 16:58 • 0 comments

  I think people with normal vision would be incapable of seeing the spectrum from the glasses.  I am extremely near sighted, and can focus on things less than a couple of inches from my eyes.  Without that ability, the spectrum would not be visible - lack of focus would turn it into a wash of color, like glare.

  
  I tried to take a picture of the spectrum using my phone, but at the short distance (centimeters) needed to make the spectrum large enough to see, the phone could not focus sharp enough to resolve colors.

  That's the best photo I was able to capture.  You can see that there's something along the edge of the bifocal lens.  It has a color, but you can't make out anything but the fact that it is there.

  I have a webcam on my workbench (Eyegore) which can focus on very close things.  I think the best thing would be to try using Eyegore to make pictures of my bifocal spectrums.
  
  

• Spectrum of an LED tube light

  Joseph Eoff • 11/09/2025 at 16:46 • 0 comments

  The light whose spectrum I could see in my glasses came from an LED tube light.  Like all its neighbors in the room, it appeared to be a "cool white." That would be appropriate, as these are lights in a work area that need to be bright and clear.

  In the resting position where I first noticed the spectrum, I could see yellow and green stripes.  Truthfully, more like "areas."  The borders were fuzzy.  They were vaguely rectangular - across a good third of the visible area from left to right, height a bit less than the width, with (from the bottom) a band of yellow and a band of green.

  
  Tilting my head up moved the image towards the red end of the spectrum.  Below the yellow was an orange colored band.  Below the orange I would have expected some red, but there was no red visible.

  Tilting my head down brought the blue and violet parts of the spectrum into view.  These areas were rather wider than for the yellow and green.  Blue and violet were both faint, though visible even in the otherwise brightly lit room.

  
  The green band had an oddity.  There was a dark stripe through the green band.  I am not sure what this says about the spectrum of light from the LED.  It is possible that the phosphor in the LED has a gap in the green area. It is also possible that there's something going on between the LED light and the green wall under the cabinets.  Maybe the pigment of the green paint has a gap in what it reflects, making the green brighter every where except in the color gap.

  It took a while to decide if the gap in the green spectrum really existed or if the supposed gap was a shadow of something on the ceiling.  The ceiling had conduits running across it, and lines from removable panels.  After a while, I realized that the gap in the green followed the slightly distorted shape of the spectrum rather than being straight like the lines on the ceiling.  The gap in the green is real - for some reason there's a part of the green spectrum missing.

  The spectrum lines were not straight.  They followed the curve of the edge of the bifocal area of the lens.
  
  

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