Aspheric questions...

[bibihang]

@zizo

One factor that you are not considering is the apparent surface area of the LED created by LED’s dome. De-doming an LED will decrease the die image size and increases the lux with an aspheric lens. I’ve tried this with both Xm-l and Xr-e LEDS with a gain in lux.

Is it? I think I saw from somewhere in this forum or other forum (can’t remember anymore) that someone explained this in details.

Note that the LED die surface area is always remain the same no matter you de-dome it or not. The dome is to collect the light emitted from the die and projected them towards a specific direction, kind of acting as an aspherical lens though. But if you de-dome it, the light would become more “scattered” since there is nothing to focus the beam.

But if you said that you have tried it practically and confirmed that you got higeher lux after de-doming the LED (every factors else remain the same), then I don’t know what’s happening behind.

EDIT: Found it, as explained by ma_sha1. You may read the following comments below, though the discussion went a bit ugly in the end…

[Manny]

@gcbryan

@DARCANGEL

@Chicago X

I work with the lens first, as the back focal length (BFL) is one of the most important considerations for host selection.

That said,is there a formula that I can follow to determine ideal bfl,in reference to the emitter type?BTW,I chose the xp-g2 because it’s new and uncharted territory and I’m up for the challenge,not sure if I’m on a fools mission or not.

I just looked up XP-G2. It’s 20% more efficient than XP-G.

It’s not uncharted territory…it’s charted just like all the other emitters.

It won’t throw as far as the XR-E.

There isn’t an ideal bfl. You just have to get the emitter at the right point with regard to the lens. A shorter bfl will give you a larger hotspot and a longer one will give you a smaller hotspot but they will both be the same brightness and will throw the same.

There aren’t that many choices regarding aspherics so you generally buy what you can and hope one of them with have the right bfl for your application.

XR-E can throw !!!