Red LED's on Housings

[Ardy]

I recently bought an AOI housing for my Oly set up and after some hours trying to get it to work I was informed that it needed multi-core (261 was advised) cables to drive the strobes.
What are the advantages of red LED's over the original white light cables that drive most UW strobes?

 

[rmorgan]

The housing has a built-in flash trigger, and it has red LEDs? I can’t think of any advantage . . . How does the command transmit from the camera to the trigger?

 

[bvanant]

The sensor that activates the strobes is something like the receiver for your TV remote. They use near IR/Red LEDs so that you don't see light coming from the remote. The sensor is most sensitive to the near IR light and in fact you can use your TV remote to make sure your strobes are firing. I haven't sent my AOI trigger signal to the spectrophotometer but I suspect it is at 840 nm where LEDs are cheap and very powerful. White LEDs have been used in some triggers, but the receiver/sensor is only using the IR part of the LED burst. I suspect you could build strobe triggers for pretty much any wavelength but near IR is a good compromise of efficient LEDs together with good transmission characteristics from your optical cable.
Here is a kind of tutorial to use some of the bits,

https://cdn-learn.adafruit.com/downloads/pdf/tv-b-gone-kit.pdf

BVA

 

[Ardy]

Interesting Bill, thanks for the lesson...

 

[Barmaglot]

Also, there is no such thing as 'white light cables'. What happens is, when a fiber optic cable is bent, the light that goes through it is attenuated to a certain degree - how much depends on the ratio between cable diameter and the bend radius; the thicker the cable, the less bending it can tolerate before losing light. A single thick cable that is coiled and bent a bunch of times is going to have significant light loss, which won't matter when you blast it with a xenon flash, but can come into play when you're trying to drive it with a relatively weak LED. A multi-core cable will have hundreds of much thinner fiber optic strands inside it, and since the individual strands are much thinner, they will have proportionally less light attenuation at the same bend radius, resulting in better overall light transmission.

 

[bvanant]

To Barmaglot's point, the minimum bend radius (0.5 dB loss) is 25 mm for the Asahi 1mm single core fiber while for the 617 core fiber it is like 1 mm.
BVA