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Author Topic: Circuit Board LED, lowering brightness.  (Read 341 times)

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Offline AlanK

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Circuit Board LED, lowering brightness.
« on: March 30, 2020, 11:01:32 AM »
Hi,

Other than lowering the voltage via resistor or using a variable supply is there a quick win to dimming down these little Circuit board LED's that I'm using in buildings?.

I had heard talk of clear nail varnish etc?.
Returnee to Model Railways after 38 years, last time I was 10 and OO Gauge, now 48 and N gauge.

Offline Railwaygun

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Re: Circuit Board LED, lowering brightness.
« Reply #1 on: March 30, 2020, 11:37:28 AM »
A yellow highlighter pen ? 
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Online ntpntpntp

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Re: Circuit Board LED, lowering brightness.
« Reply #2 on: March 30, 2020, 12:40:37 PM »
Yeah some sort of semi transparent filter will do the job.   A good excuse to chomp through some Quality Street perhaps?  :D

Reduce the current through the LED (not the voltage  :no:  )  with an additional resistor.  They cost pennies, and it means you're reducing the load on your power supply so you can run more LEDs  :D
Nick.   2016 celebrating the 20th anniversary of "Königshafen" exhibition layout!

Online Malc

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Re: Circuit Board LED, lowering brightness.
« Reply #3 on: March 30, 2020, 01:35:13 PM »
I used a yellow ochre watercolour paint. Not only dims the light, but gives it a period look.
The years have been good to me, it was the weekends that did the damage.

Offline LASteve

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Re: Circuit Board LED, lowering brightness.
« Reply #4 on: March 30, 2020, 09:33:31 PM »
Ditto. I dab some thinnned acrylic paint onto the LED. You can change the "temperature" of the light using different colors - white for a bright look, yellow for a more "light bulb" look, red for a softer look, for example a country pub interior.

Offline AlanK

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Re: Circuit Board LED, lowering brightness.
« Reply #5 on: March 30, 2020, 11:00:55 PM »
Thank you, some good ideas there and luckily I have the paint(s) handy as well. I take it there is normally no issue with heat on these?
Returnee to Model Railways after 38 years, last time I was 10 and OO Gauge, now 48 and N gauge.

Offline Only Me

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Re: Circuit Board LED, lowering brightness.
« Reply #6 on: March 30, 2020, 11:25:02 PM »
I used acrylic it works well to reduce brightness



Online Bealman

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Re: Circuit Board LED, lowering brightness.
« Reply #7 on: March 30, 2020, 11:26:34 PM »
If your LED gets hot, it's just about to pop!!

There should be little or no heat if the current is correct.
Vision over visibility. Bono, U2.

Online Malc

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Re: Circuit Board LED, lowering brightness.
« Reply #8 on: April 01, 2020, 11:58:05 AM »
And if you overdo the paint, you can always scrape it off.
The years have been good to me, it was the weekends that did the damage.

Offline AlanK

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Re: Circuit Board LED, lowering brightness.
« Reply #9 on: April 01, 2020, 12:19:35 PM »
Added some yellow ochre yesterday, wonderful antique glow now, thank you all very much. 
Returnee to Model Railways after 38 years, last time I was 10 and OO Gauge, now 48 and N gauge.

Offline IanF

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Re: Circuit Board LED, lowering brightness.
« Reply #10 on: April 01, 2020, 05:21:29 PM »
I get the Voltage - Voltage drop / mA calculation to achieve the 'standard' brightness for the LED. To reduce brightness an we just put a larger resistor into the mix I thought  Also there will be different forward voltages and current depending on the colour of the LED. I suppose you could make up a breadboard and test different resistors to get the effect you want (or simply paint it - let's face it that is easier) but if anything like me I like to experiment and see what works.
For instance today I put a 13.8V supply to a green LED an a blue LED through a single 1K resistor. Too bright man, too bright. Went all the way up to 10K and to me still too bright. So I thought I would teach those LEDs a lesson and slapped a 100K resistor on. Bingo - the green light seemed about right but the blue light was a little too dim.
Help - I don't know what I'm doing

Online ntpntpntp

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Re: Circuit Board LED, lowering brightness.
« Reply #11 on: April 01, 2020, 05:45:33 PM »
@ianf   yes exactly - I find there's no need to run these small LEDs at anything like their "rated" current.

For trial-and-error determination of a resistor for suitable brightness I use a really cheap resistance box - as has been discussed on another thread on here.  The only warning I would give is the box I have shorts to zero ohms when switching between 4 and 5 on the dials, so I have to remember to cut power first!

https://www.ngaugeforum.co.uk/SMFN/index.php?topic=46734.0


Using a single resistor with 2 LEDS of different forward voltage  in parallel  may result in the higher voltage one not lighting at all.  Run them in series with a single resistor if you want both to share the same current.
« Last Edit: April 01, 2020, 05:49:36 PM by ntpntpntp »
Nick.   2016 celebrating the 20th anniversary of "Königshafen" exhibition layout!

Offline ronp849

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Re: Circuit Board LED, lowering brightness.
« Reply #12 on: April 02, 2020, 12:25:42 PM »
What are you using to drive it? If it is available, PWM control would dim it for you.

Ron

 

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