LED House Sign

[sammy004]

Hi friends I am building a LED house number sign and I have the leds all hooked up I am using 3 leds to 1 120ohm resistor and when I look at the sign it looks like a few sets of leds are brighter thenn the other I have a pic to show can someone tell me what I can do to make them all the same. brightness or what I am doing wrong? your help will be greatly appreciated.
Thank you
**broken link removed**

 

[Hero999]

Please post the schematic?

Are the LEDs wired in parallel or series?

If they're in parallel did you use a separate resistor for each LED?

If not then that's the problem, each LED will have a slightly different voltage drop and the ones with the lower drop will hog all the current and be brighter than the rest, they'll also fail first, after which they'll drop like flies.

 

[audioguru]

I think the LEDs are cheap with a very narrow focussed angle to make them appear bright only when they point directly at you and some are a little crooked. Better LEDs are bright over a wide angle.

 

[sammy004]

They are wired as +----|>|----|>|----|>|---/\/\/----- R = 120 ohms then +----|>|----|>|----|>|---/\/\/----- R = 120 ohms and so on power is 12 volts

 

[sammy004]

I think the LEDs are cheap with a very narrow focussed angle to make them appear bright only when they point directly at you and some are a little crooked. Better LEDs are bright over a wide angle.

I think that may be the problem so I ordered 100 more LEDs hope they work but I hope what I am doing is right if not please correct me.

 

[audioguru]

The LEDs should have an angle of 40 degrees or more. Very cheap LEDs have an angle of 10 degrees or less.

What is the angle of the ones you have and what is it for the ones you have ordered?

 

[sammy004]

The LEDs should have an angle of 40 degrees or more. Very cheap LEDs have an angle of 10 degrees or less.

What is the angle of the ones you have and what is it for the ones you have ordered?

Here is the info
Product Name LED
Emitted Color Blue
Size (mm) 5mm
Lens Color Water Clear
Peak Wave Length (nm) N/A
Static Sense Yes
Forward Voltage (V) 3.0 - 3.4
View Angle 25 - 30°
Luminous Intensity (mcd) 6000
Maximum Current 20mA Continuous, 50mA peak for 10% Pulse Width
Item Net Weight 95g / 3.4oz

 

[audioguru]

Is that what you have shown or is that what you have re-ordered?

 

[MrDEB]

could just place a plastic cover over sign as a difuser.

 

[sammy004]

Is that what you have shown or is that what you have re-ordered?

Oh sorry thats what I have ordered.

 

[sammy004]

could just place a plastic cover over sign as a difuser.

Yeah and tint it slight black like a smoke color?

 

[Hero999]

That will just reduce the light intensity.

Dark plastic can be used to increase the contrast on segmented LED displays but that doesn't matter here.

You'll find that lightly sanding the plastic LED case will increase the viewing angle because it'll make it into a more diffused LED as the rough surface will cause light to scatter more.

It appears to be a quality problem. The LEDs should all be a similar brightness, not some very dim and others very bright. It sounds like the LEDs are cheap and nasty Chinese knock-offs.

 

[Gayan Soyza]

Oh........That blue colour clear LED's are so brighter & cannot see directly its very hard to see for postman's.

You can add a contrast filter (very hard to find) the ones I used in my LED signboards.I use mat LED's not clear ones like yours.

 

[sammy004]

so my setup of the led's is that OK though?

 

[Hero999]

I can't see anything wrong with connecting them in strings of three in series, with a resistor for each string, you did the right thing, it must be the LEDs, perhaps you should ask the person who sold them to you?

 

[audioguru]

Cheap Chinese LEDs all have different voltages and different brightnesses.
If they are all physically pointing in the same direction then the actual narrow beams are shining over here and over there.
Some LEDs are bright and others are dim.
They are hopeless.
BUT THEY ARE CHEAP SO YOU SAVED MONEY! And everybody who sees them laughs at you.

My good LEDs are made by Agilent and Fairchild. They are absolutely perfect.

I bought some cheap blue Chinese LEDs in a local store but their colours were all different.
I bought some more cheap Indian LEDs in a local store but only half worked.

 

[sammy004]

perhaps you should ask the person who sold them to you?

I'm afraid that will not be possible because that person is on the other side of the world. I think you guys are right the LED's were cheap and bad hopefully the new ones will be better

 

[sammy004]

BUT THEY ARE CHEAP SO YOU SAVED MONEY! And everybody who sees them laughs at you.

I don't think no one will be laughing because I will not put it outside if it looked like that. I suppose your saying that because you got laughed at one time? It's OK if you did right because thats how you learn right.

How much are your LED's?

 

[audioguru]

There are cheap-looking LED house numbers on my street. I have never made one.
I have never bought cheap Chinese junk on E-bay but I have read about the horrors from and about other people.
Digikey and Newark sell name-brand high quality parts. They are delivered (from another country: USA) the next morning.

 

[sammy004]

But isn't everything made in China? Everything I see says "Made in China" Would that be considered junk as well. Like my 52" Sharp LCD.