kramer5150
Flashaholic
Curious... do thinner lenses obstruct less light than thicker ones (all else being equal)?
Flashlight lens, transmission efficiency?
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Flash_Gordon
Flashlight Enthusiast
No. Assuming identical material. the index of refraction is the same. The index of refraction in a vacuum is 1.000, air about 1.0003, distilled water about 1.33and the types of glass we use in flashlight windows about 1.5-1.6. The depth of the material, assuming a pure and consistent medium is not a factor.
While logic would tell us that a 2mm window is twice as thick as a 1mm window and therefore must block more light, we need to relate this "double" thickness to the wavelength of visible light.
Visible light is in the wavelength range of 400-750nm. A nanometer is equal to 10-6 mm. So the wavelength of the visible light we care about is so short that the difference between a 1mm or 2mm window is irrelevant.
Significant loss is caused by internal reflection between the 2 surfaces of the glass. The behavior of this incident light will cause a loss of transmitted light through the window. Surface coatings or multi coatings can greatly reduce this factor but not eliminate it.
Mark
While logic would tell us that a 2mm window is twice as thick as a 1mm window and therefore must block more light, we need to relate this "double" thickness to the wavelength of visible light.
Visible light is in the wavelength range of 400-750nm. A nanometer is equal to 10-6 mm. So the wavelength of the visible light we care about is so short that the difference between a 1mm or 2mm window is irrelevant.
Significant loss is caused by internal reflection between the 2 surfaces of the glass. The behavior of this incident light will cause a loss of transmitted light through the window. Surface coatings or multi coatings can greatly reduce this factor but not eliminate it.
Mark
Last edited:
This is correct despite what FG says.
Justin Case
Flashlight Enthusiast
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Of course there is a dependence on amount of absorption vs thickness. Google Beer-Lambert Law.
2xTrinity
Flashlight Enthusiast
Yes, but light loss due to absorption in the glass on the order of ~mm thickness is insignificant compared to the ~4% reflected from the front and back air-glass interfaces.
Note that while these multiple reflections (for uncoated glass) cause 8% of the incident light to be reflected, this does not necessarily mean 8% lumen loss. In many cases, some of that light will bounce off the reflectors again, then eventually make it back out again as diffuse sidespill.
