About Red LED

Hoya

Newly Enlightened
Joined
Oct 24, 2004
Messages
191
Why it is that my red LED SF A2 has more artifacts/rings than my white LED A2? This also happens in my Inova 24/7. On the white LED the beam is a smooth/even flood, the red beam has some rings. What causes the rings?
 

evan9162

Flashlight Enthusiast
Joined
Apr 18, 2002
Messages
2,639
Location
Boise, ID
[ QUOTE ]
LightScene said:
The rings are caused by the optics or the reflector, not the led.

[/ QUOTE ]

It definitely is the LEDs...

In a white LED, the phosphor covering the blue LED die smooths out the beam.
The die of a colored LED is bare, so light emitted is emitted from a few surfaces, reflected off some surfaces, and shadowed by the bond wires. It's a complex emitting surface, and is prone to producing rings and splotches.

The phosphor in a white LED is a (relatively) smooth surface, so is much more uniform in emitting light. In white 5mm LEDs and low dome luxeons, the phosphor is more of a glob, covering a large part of the die and reflector cup, and is a larger, more circular surface producing light, so it tends to be a wider smoother beam, and more uniform. A high-dome luxeon has a square phosphor deposit, so it is still smooth, but optics will tend to produce a square beam pattern.

In contrast, for a 5mm colored LED, you get direct light from the surface of the die, plus some reflection in a ring from whatever light reflects from the reflector cup, which explains the ring/dark ring/spot that you see with a lot of colored 5mm LEDs. The die has a rectangular emitting surface, often with the corners chopped off where the bond wires connect.

With a colored luxeon and an optic, you see the grid pattern of the Luxeon die projected forward - there is a dark ladder-like shadow cast because the die of a Luxeon has a grid of opaque conductors over top of the emitting junction, shadowing some of the light produced. In a white Luxeon, that ladder pattern is nearly eliminated because the phosphor is a uniform surface and mostly makes up for the non-uniform pattern of the die underneath.
 
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