Fibre optics issues

Brucebruce · Post by **Brucebruce** » Wed Jul 09, 2014 6:54 am

Hi all!

Hopefully someone can help me.

I'm currently building the Moevius/revell battlestar galactica. I'm lighting it and I'm more or less doing the same thing as this guy:

http://secretsmodelling.webs.com/moebiu ... actica.htm

I'm having trouble with the red lights though. On his pictures the red led connected to the fibre optics are shining spot lights onto the bits below. Mine aren't doing that. The light transfer seems to be very weak. It seems to be fine when I'm using lights that aren't red. I've tried two different types of red led, I've applied heat to the ends of the led to mushroom them a little and I still can't seem to get it to work. Obviously if you look at the end of the fibre you can see the red light but it doesn't seem to be shining bright enough to show up on the actual model. Any ideas?

Also, and this doesn't need answered but I'm just curious. I'm using a 12v power source and my individual white/blue leds need a 390 ohm resistor. Am I right in thinking it'll need to be a higher resistor for the red leds as they have a lower voltage?

Thanks for any help you can provide!

b5ranger99 · Post by **b5ranger99** » Wed Jul 09, 2014 11:32 pm

The red LEDs have a different voltage and current requirements.
Based on what I could find the red LEDs should be brighter then the blue and white, so I must have missed something. Could you list the specs, voltage and current of the red, blue and white LEDs?

Are the red LEDs brighter at the LED and dimmer at the end of the fiber optic?
If so it is possible, not likely, that the fiber you have doesn't pass red light as well as other colors.

Just my two cents

Brucebruce · Post by **Brucebruce** » Thu Jul 10, 2014 7:11 am

Hey,

From what I understand red LEDs have a forward voltage of 2V and forward current of 15mA.

The led seems to be running normal and the ends of the fibre are certainly lit , just not very brightly.

The fibre is 0.5 mm. No idea what's going wrong!

Ant · Post by **Ant** » Fri Jul 11, 2014 7:41 am

What's more likely to be the issue here is the light output rating of the LEDs in question.

Measured in candelas (cd) or milli-candellas (mcd) (1 cd = 1000 mcd) it can range from the dim end around 10 mcd up to hyper bright 10's of cd.

As technologies have improved it's become possible to push out more and more light for the same current requirements - so the 10 cd LED will still only need 20mA and still have a forward voltage of a couple of volts.

If you want really bright FO output, you need to be looking for LEDs at least 1 cd. Ironically these shouldn't cost any more than less bright devices.

Here's a typical high brightness red - 4.5 cd yet only 22p in UK money
http://www.rapidonline.com/electronic-c ... cd-55-0880

Ant

Brucebruce · Post by **Brucebruce** » Fri Jul 11, 2014 10:35 am

Ahh thanks! I always assumed that when you saw super bright LEDs on eBay they were using a little poetic license!

That makes sense as all the LEDs it's working with I've bought from an led supplier but the red ones I have are from a super cheap multipack from a shop.

I've ordered some and will give it a go!

Thanks again