Question for Telephony


Flashlight Enthusiast
Feb 2, 2002
Can you say, \"Durian\"?
Just bought a PT Impact, and I'm as amazed as you by the power and quality of the optics. *But* - it did show up something about LEDs that might plague other torches like the Impact: somewhere along the beam, at its sharpest point of focus (not beam focus, but lens image focus) you'll see the LEDs bond wires, magnified tens of times!

For eg, my Impact displays its LED bond wires when held about 4.5-5.5 inches away from any surface. At this distance, *each* of the bond wires casts a thin shadow about 2/3rds of an inch. Actually, its more like an image of the chip and the bond wires! This shadow is still visible at greater distances, but far less pronounced.

Question: Is there any way an LED could be manufactured such that the bond wires are invisible? If so, do any specimens exist in your extensive museum, or anywhere?

Thanks in advance for answering this!


Apr 4, 2001
See my post in this thread:
5 Watt Luxeons
Lumileds, Inc. has published a number of technical papers describing a method to make all electrical connections to the LED on the bottom. This way the whole top surface can emit light without obstructions (like bond wires and metalization patterns). Not only will this be optically more efficient, it will eliminate the effect you noticed of artifacts in the LEDs light.

However, they will probably continue to make square LEDs because it's easy and it doesn't cause them to waste part of a working LED by trimming it to a circle. They make LEDs on a large circular wafer, then cut the wafer into individual LEDs. It would be difficult to cut them into anthing but a square or rectangle. If they got very clever they might be able to do a Hexagon, or bite the bullet and trim the perfectly good squares into circles - but thats wasteful of very expensive post processed material. So you may continue to see the shape of the square in the emitted light.

This special mounting process is more expensive than the common practice of gluing the LED chip down, and attaching a bond wire - like all common LEDs are made. Therefore it is unlikely to be used by anyone but Lumileds and any other company that might start making "expensive" illumination type LEDs with large LED die (chip) size.