OT: TIR Lenses (total internal reflection) Wrongly named so?

[bgifford]

Total internal reflection TIR would mean that the light is totally refracted back to the inside of the plastic lens.

Just imagine that it says "Plastic TIR Lens" and not "Water" on this diagram. Also imagine that the "incidence ray" is the light coming from the leds. TIR is possible because n1>n2, however the radions obviously have a concentrated refracted ray (that gets to the tank and corals). The TIR lenses would have to exceed the critical angle and be totally reflected back to the inside of the lense in order to be classified as TIR- which doesn't happen, and you wouldn't want that anyways. Just something to think about.:beachbum:
<a href="http://imgur.com/S3YFvLX"><img src="http://i.imgur.com/S3YFvLX.png" title="Hosted by imgur.com" /></a>

 

[evolved]

I think you're looking at this from the wrong perspective. If you consider the blue as air, and the white as the plastic lens, then you'll see what the TIR label implies is that all light is reflected out of the lens, and none is lost to scatter and/or absorption within the lens itself. Which does indeed align with undesirable consequence you mention of a non-TIR lens.

 

[bgifford]

I think you're looking at this from the wrong perspective. If you consider the blue as air, and the white as the plastic lens, then you'll see what the TIR label implies is that all light is reflected out of the lens, and none is lost to scatter and/or absorption within the lens itself. Which does indeed align with undesirable consequence you mention of a non-TIR lens.

Total internal reflection has a self descriptive definition. If the tir lenses actually caused total internal reflection, that would mean that the light is kept within the lens. The diagram represents air and water, but the important thing to note is the refractive index values. The medium with a higher index of refraction (water or plastic) is the medium that the light will be reflected into. Likewise the medium with the lower index of refraction IR (air) will be the cause of the light bending away from the normal (the dotted line). An angle of incidence greater than the critical angle will cause the total internal reflection off the surface of the medium with low IR and back into the medium with which the light came from.

Likewise, an angle less than the critical angle will REFRACT the light into the air at an angle following snell's law of refraction: n1sintheta1=n2sintheta2
n1= index of refraction of the incidence light ray's medium
n2= index of refraction of the refracted rays medium


If the air (white) on the diagram represents the plastic tir lens, and the water (blue) on the diagram represents the air, the diagram will look the same except the arrows will be opposite and the labels n1 and n2 will be swapped. The same concepts hold true either way we change the diagram.

They used the physics term incorrectly.

 

[evolved]

I understand the physics. My point still stands; you're looking at this from the wrong perspective (specifically the word "internal"). It's not internal to the optic, it's internal to each respective light wave. Each light wave experiences total internal reflection when they contact the plastic reflector of the optic (assuming a TIR optic).

 

[bgifford]

I understand the physics. My point still stands; you're looking at this from the wrong perspective (specifically the word "internal"). It's not internal to the optic, it's internal to each respective light wave. Each light wave experiences total internal reflection when they contact the plastic reflector of the optic (assuming a TIR optic).

i'm not exactly sure what you mean by "Each light wave experiences total internal reflection when they contact the plastic reflector of the optic"

i'm assuming the transfer of light from the plastic to the air, and i'm only recognizing the transfer according to the medium of each respective refractive index. The problem gets more difficult if you consider the light is emitted through glass initially, to air, to plastic lense, to air.

If you are suggesting total internal reflection occurring from air to plastic, then that would not follow suite with the equation. n1 has to be greater than n2 and if we said Air to plastic then n1AIR<n2plastic.