auto gauge bulb to led questions

[augidog]

Hi, thanks for the forum.
I have an older Porsche with 1.5 volt poorly lit gauges.
I'm starting slowly with 5- 18000 mcd 5mm led's with a 20 degree angle. 3 small oil/boost/volt gauges.
The problem I see is that the OEM bulb gives off a wider beam illuminating the whole gauge back allowing just enough to encircle the back plate edges illuminating the gauge.
  My thought is to drill into the back and outer edge of the gauge exactly the width of the led and insert the leds around the perimeter.
My question is at what spacing and what depth can they handle in reference to light loss and overlap?
I don't want any breaks in the illumination and I do want brighter
Will the placement into the metal case help in heat transfer or hurt?
The smaller gauges are 6.5 inches in circumference and 1 1/8th deep
Thanks
I'm looking at  45000 5m  25 degree on the larger 12.5 x 2" main gauges.
Picture to follow -not enough time  tonight to post them.

[Rob]

Welcome to the boards.

The spacing and depth question is something I'll say you may just have to feel your way through, possibly on a 1:1 scale prototype. I can tell you I'd be tempted to diffuse the light from the LEDs I have in hand, probably by sanding the case or even drilling it. To me the best solution would involve just a drop-in replacement for the incandescent lamp you have. (no issues when it's time to sell later)

You can also make a "light pipe" out of acrylic sheet or rod to help distribute the beam more to your liking. In the past I have used heat shrink tubing to "couple" an LED to a piece of 5mm acrylic rod to get a different shape.

On the heat questions, I'd say for the amount of LEDs you are needing, it's not too big a concern either way.

[augidog]

First LED arrived today. 20,000 mcd  angle of 25.
 It is just a little duller than oem 1.5 bulb but it has a great blueish tint from the white LED.
I think the 45,000 mcd will do it. Very nice display hopes
Has anyone used a lm3914 bar display driver?

[seanyiya]

Isn't LED will be poorly lit with 1.5 v power?? red and amber will be lit, but blue, white, green..... 

[Rob]

Sure, LM3914 is a well-known part around here. The sample applications in the datasheet are all quite buildable.

Did you have any specific LM3914 questions? Feel free to open anoher thread if so.