6" Long Reflector on E21

[The_Driver1 (The_Driver)]

@Joshk

@The_Driver

Printing a reflector seems like a cool idea!

Just a note here:

If you want throw you need to make a reflector with a large diameter. The front facing surface area (as if it were a flat circle) determines the throw, not the depth.

Actually, the front facing surface area is predetermined by the focus-to-vertex distance of the parabola. The LED phosphor surface is the focus in this case. And the vertex is the bottom point of the parabola. The vertex is below the LED, so is theoretical in this case, but it still exists in the geometry. If you want best throw, you do like I did and move the focus down near the vertex. This tightens up the shape and adds light to the hotspot. If you want mostly flood, you move the focus outward, widening the shape of the parabola. This lets more light escape the hotspot and become flood. And actually the length has the same effect, where longer reflectors add more light to the hotspot. In my case, I maximized the hotspot with a short focus and a long reflector, and got a laser-like result. *This post edited for clarity.

This is a common misconception. It doesn't work like that. The "tightness" you mention is not actual throw (range), but just the shape of the hotspot. A smaller hotspot does not neccessarily mean that it actually goes further. The luminous intensity (measured in candela[cd] or lux @ 1m) determines the throw.

You can actually calculate it:

luminous_intensity [cd] = luminance_of_the_light_source [cd/mm²] x area_of_the_reflector_or_optic_as_seen_from_the_hotspot[mm²]

Imagine that you are the hotspot some distance away from the flashlight. You can't see how deep the reflector is (you see a flat circle lit up by the LED).

area_of_circle = pi x radius²

radius = diameter / 2

As you can see the area is mainly determined by the outer diameter of a circle. This has by far the largest influence on the area.

The depth of a reflector (for a given outer diameter) only has a tiny influence (a deeper reflector for a given diameter usually has a smaller hole for the lightsource => this increases the area of the reflector slightly). The depth mainly influences the shape of the beam. A deeper reflector decreases the size of the hotspot, increases the size of the corona around the spot and decreases the emission angle of the outer spill.

You can test this yourself by doing a few measurements or by using the calculators here.