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Author Topic: What's a "bright enough" LED for this project?  (Read 1034 times)
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I'm looking for 20 bright RGB LEDs for a project. Each will go inside a 3" Japanese paper lantern. I tried the LEDs that come in the Arduino Starter Kit and they aren't nearly bright enough for this.

My problem is that looking at the Newark page for LEDs is extremely confusing as there are SO MANY variables available. I don't know enough to be able to make an informed purchase. For example, I read about millicandela and lux but the Newark page doesn't seem to even have that unit when you are filtering their product list. I'm also trying to wrap my head around Ohms law and at the same time experiment with LEDs without blowing my Arduino so when they ask for "forward current/voltage" I have no idea what to choose.

While we are at it, I've bought some cable at RadioShack that I'm planning to use with these LEDs. How far will I be able to go with it? I'm thinking that I will need to go some 2 or 3 feet for some LEDs and 6 to 10 feet for others. Will I run into any problems with these lengths? The side of the cable reads "E202888 AWM 1007 20AWG 80°C 300V VW-1".

Thanks in advance!
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I recently used some SMD green LEDs for a project.  They were tiny, but rather bright.  3.3V forward voltage, 20mA, 2700 mcd.  I ran them at 18mA.  You can read more about the project and see the video here.  If you want the specific LED I used, let me know.
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There are 2 parameters that you will see quoted. Luminous flux (usually measured in lumens) measures the total amount of light emitted by the LED. For reference, a 50W halogen bulb emits around 800 lumens.

Radiant intensity is usually quoted in candela for visible lighting, and mW/sr for infrared emitters. This specifies the amount of light emitted per unit solid angle. So a 50W spotlight and a 50W ordinary light bulb might both emit 800 lumens, but the spotlight emits most of it in beam (specified by half-angle or full-angle, often just called viewing angle) rather than in all directions, and looks brighther (if you look at it down the beam). So the radiant intensity is the best measure of how bright the LED will look, provided that you are looking at it head-on.

So I suggest you  look for LEDs with a sufficiently high candela value, and check that the ones you eventually select have a wide enough viewing angle for your application. This http://uk.farnell.com/kingbright/l-154a4surkqbdzgw/led-multi-colour-rgb-5mm/dp/2290374 is the brightest through-hole RGB LED that I found.

That wire you quote  is 20AWG, which has a resistance of 0.033 ohms per metre. It will be fine for that application.
« Last Edit: April 11, 2013, 04:02:42 am by dc42 » Logged

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I'm looking for 20 bright RGB LEDs for a project. Each will go inside a 3" Japanese paper lantern. I tried the LEDs that come in the Arduino Starter Kit and they aren't nearly bright enough for this.

I find 10mm RGB LEDs are much brighter than 5mm ones, even though they look similar on paper.

http://www.ebay.com/sch/i.html?_nkw=10mm+rgb+LED+common+anode

For a lantern you probably want a wide viewing angle (140 degrees) and clear plastic, not diffused.

The figures quoted by manufacturers are confusing, yes. There's a few ways they can inflate the numbers by quoting narrower viewing angles or whatever.

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Valencia, Spain
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While we are at it, I've bought some cable at RadioShack that I'm planning to use with these LEDs. How far will I be able to go with it?

A long way.

I'm thinking that I will need to go some 2 or 3 feet for some LEDs and 6 to 10 feet for others. Will I run into any problems with these lengths?

No.

The side of the cable reads "E202888 AWM 1007 20AWG 80°C 300V VW-1".

20AWG is massive for a 20mA LED.
« Last Edit: April 11, 2013, 09:22:31 am by fungus » Logged

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20 LEDs will somewhat of a challenge with only 14 outputs, won't it?
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14 digital + 6 analog = 20
He mentioned using 20 RGB LEDs, which means he probably needs 60 outputs (20 R, 20 G, 20 B = 60), assuming they want to control each LEDs color independently.
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Or just two pins (plus VCC and GND) is they use something like a WS2801, or a single pin if they're using WS2811 embedded RGB LEDs.
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Quote
I read about millicandela and lux but the Newark page doesn't seem to even have that unit when you are filtering their product list.
While it is not in the filter parameters it is in the listing along with other things like the price. You can click on the brightness column and sort the results by brightness, handy when there are many pages. 
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Thanks everyone for the info.

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dc42 "For reference, a 50W halogen bulb emits around 800 lumens."
This is a great reference as I'm very familiar with how bright common lightbulbs (that are measured in Watt) are! Thanks!

Based on the suggestions here I've gone ahead and bought myself some RGB LEDs. We'll see how that goes!

As far as pin count I'm not too concerned. I've recently learned how to use shift registers and using them with the ShiftPWM_RGB library to control RGB LEDs is kids play! 
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Manchester, NH
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> 14 digital + 6 analog = 20

The 6 analog pins are input, not output. I did miss the RGB part though so, with the 14 pins can only light 4 RGB LEDs without adding multiplexers or drivers.
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