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 Using LEDs to replace tiny light globes
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 Return to top of page · Post #: 1 · Written at 6:38:57 AM on 8 April 2019.
Robbbert's avatar
 Location: Sydney, NSW
 Member since 18 September 2015
 Member #: 1801
 Postcount: 1276

Some equipment from the 80s and 90s had these tiny 12 volt globes to light up meters, dials, etc. The globe had 2 wires coming out (it didn't screw in to a socket). I've found these things to be incredibly unreliable, and I'd like to replace some with LEDs of the same size and brightness.

Question: Do such LEDs exist? If so, what is the value of the series resistor to be used?

In the case of 2 or 3 globes, I'd like to put the replacement LEDs in series, to keep the current draw down - and only need one resistor.

In these cases what would the resistor values be? Also, what LED would you recommend?

 Return to top of page · Post #: 2 · Written at 10:03:00 AM on 8 April 2019.
Normf's Gravatar
 Location: Erowal Bay, NSW
 Member since 19 June 2018
 Member #: 2256
 Postcount: 87

Hi Robbbert
There should be available LED of a similar physical size that would replace those bulbs.
As you are only needing about 10mA to run a led, I would start of with about a 1k resistor
and adjust the value to get the required brightness similar to the bulbs you are replacing.
Having a quick look on ebay there are 5mm and 3mm round LEDs,
You could run them in series or parallel using a single resistor.

 Return to top of page · Post #: 3 · Written at 5:38:06 PM on 8 April 2019.
Brad's avatar
 Location: Greenwich, NSW
 Member since 15 November 2005
 Member #: 1
 Postcount: 6061

If the globes are the ones I am thinking of, a 3mm LED would be about the same size however you are not likely to match the colour temperature. If this isn't a concern then the rest just involves the changeover from globe to LED. If Norm's suggestion works, the job shouldn't cost more than a tenner.

A valve a day keeps the transistor away...

 Return to top of page · Post #: 4 · Written at 8:47:33 PM on 8 April 2019.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 4122

A lot of the supermarkets do either quote current, or have data on the LED.'s they sell.

 Return to top of page · Post #: 5 · Written at 8:14:25 AM on 9 April 2019.
Wa2ise's avatar
 Location: Oradell, US
 Member since 2 April 2010
 Member #: 643
 Postcount: 759

I've used LEDs from Xmas light strings to replace panel lights in ham and CB radios. The LEDs are roughly the same diameter of the old light bulbs. The Xmas light LEDs have inverse cone shapes molded into their plastic cases. This cone distributes the light roughly evenly, compared to regular LEDs that aim most of their light in one direction.

I'd try a resistor of 10K for a power supply of 12V. Modern LEDs don't need much current.

 Return to top of page · Post #: 6 · Written at 9:45:58 AM on 9 April 2019.
Irext's avatar
 Location: Werribee South, VIC
 Member since 30 September 2016
 Member #: 1981
 Postcount: 343

The trouble with LED's replacing those little incandescent globes is that the LED doesn't throw much light sideways and when it's used to illuminate a dial by being inserted at one end the results are often disappointing.
LED's are usually quite directional.
Sometimes you can fiddle with positioning of the LED and get an acceptable result.
Worth a try anyhow.

 Return to top of page · Post #: 7 · Written at 11:43:47 AM on 9 April 2019.
Kakadumh's Gravatar
 Location: Darlington, WA
 Member since 30 March 2016
 Member #: 1897
 Postcount: 137

When you run a LED on AC the colour temp seems to go batty. A Red Led is bright red on a DC supply but more like an orange colour on AC which may be due to the fact that the LED is meant for DC use and on an AC supply it is only seeing half wave pulses so not being fully energised.


 Return to top of page · Post #: 8 · Written at 3:00:50 PM on 9 April 2019.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 4122

At the end of the day: It is a diode

 Return to top of page · Post #: 9 · Written at 3:35:08 PM on 26 April 2019.
Wirelessfan's avatar
 Location: Sydney, NSW
 Member since 26 April 2019
 Member #: 2349
 Postcount: 18

I have used a short length of adhesive strip that has SMD leds-cut to length, has integrated resistors, 12volt approx. Ebay cheap.
It replaced a tiny fluro tube in back of a studio clock, worked well...might work for you.

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