Why aspheric lens (plano convex) is used in long thrower flashlights instead of biconvex lens?. I have large diameter biconvex lens. Can someone please explain it?
Not really.
Ever try it? See if you can focus A Bat Signal from the emitter on a nearby wall. If an image forms, it should work as well.
Convex lenses concentrate the light. And it does not matter if you have a biconvex lens, a plano-convex lens or even a concave-convex lens (yes they do exist). What matters is the focal lenght of the lens. The latter you can check out for yourself by trying to concentrate the light of the sun on a piece of paper. The distance between the centre of the lens and the object you’re shining on is called the focal lenght of the lens. I’m not sure but IMHO the plano-convex lens is the most common because it is cheapest to manufacture. The other side being flat, there is only one side to be processed carefully.
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I tested that biconvex lens only collects light if pre- collimator lens is placed in front of LED but it makes the beam thicker with less range.
But aspheric lens still makes tighter and bright beam even without RLT collar.
I’m not sure, but I think that biconvex lenses are thinner for the same focal length, and therefore have better transparency and less light loss (while using the same glass material).