I received a LS return this week that was not posted here on the CPF. In fact it is the first LS return we have received.
Both lights in the return worked to spec. I was a bit curious so I called the customer to find out why they were returned.
The reason for the return was the beam quality of the LS LED. Specifically the centering of the beam, the yellow corona and the blobby center.
I explained that these where all normal for the LS LED and within spec. I told him that I would post another note on the CPF further warning people about this LED so they are not surprised when they receive their LS.
Other LED flashlights of this brightness level utilize a cluster of Nichia 5mm LEDs. Although the Nichia cluster will be bulkier, not throw as far and be less efficient, they will produce a smoother, more uniform beam.
This is caused by several factors:
1. Nichia LED technology is older (or "more established") and therefore they can provide precise half -step bin ranking. This provides a more uniform tint and brightness among multiple samples.
2. The Nichia Die operates at a lower surface energy. I venture to say that they are also more uniform (less "hotspots"). This provides less tint/brightness/beam uniformity variations.
3. The Nichia integral lens is less focused. This tends to blur any hotspots or beam imperfections and makes centering less of an issue. In the LS, the higher magnification used in the lens also magnifys the features of the die/bond/phosphor. If you stare at a LS beam w/optics you can see quite a few details in the beam. I think this more focused lens in conjunction with a different phosphor geometry also creates the "corona" effect.
4. Used in an array, the multiple light sources blur together and hide imperfections compared to a single point source LED.
Of course at this point, some may ask, "why even use the LS LED?". Because it is more compact, efficient and focused.
Lumileds is refining their technology. However, I sometimes get the impression that beam quality takes a slower track than their die output research. They really do have the best dies going as far as sheer luminosity.
Will the LS LED reach Nichia smoothness while maintaining their efficiency edge? Probably not this year.
So the question I pose to you today is: Is it worth using a LED with a inferior beam quality just because it produces more lumens for a given size and power source?
Incidentally, the two units that where returned where very quickly "reassigned". We didn't have any production LS at all since we shipped every single one of them to you. One is going to Gibson and the other one is now my EDC.
Peter Gransee
