Which LED do I need. - Page 1
Forum section: electronics / beginners

author: Joshua
author_rank: Regular Contributor
timestamp: August 19, 2010, 02:47:56 am
content: Hello everybody.Before I start I would just like to say that I know this is probably a super retarded question, but nonetheless, I can't figure it out.I'm ordering some stuff to start making some circuits and what not. I'm not a total beginner as I know a fair amount about electronics and have played around with such stuff before.I'm going to order some LEDs to play around with. The problem is, when I go to Digi-Key and Mouser, there is just so many different led's that I don't know what the difference is. So here's what I'm wanting, if such a thing exists. I just want a standard LED, that's affordable and useable for a wide range of circuits. I plan on using some PICs if that means anything.So my questions are:What is the standard size of LED (just the regular common LEDs you find in everthing)?What current draw should I look for?What operating voltage should I look for?Also, if anyone has any part numbers or anything I would greatly appreciate it.If there's anything that i left out that I should know, I would be thankful for that information.Thanks,PianoKid1994

author: DJPhil
author_rank: Frequent Contributor
timestamp: August 19, 2010, 02:56:16 am
content: Assuming no special needs, the most common LED sizes are 5mm and 3mm. Forward voltage will depend on the color, and they'll be designed for about 2mA to 10mA (choose resistor accordingly). The cheapest ones you can find are probably just fine. When you have an application in mind you'll probably start looking into other things like power, high efficiency, viewing angle, diffused vs. clear, and multiple colors.I haven't shopped around for LEDs at the big houses like Digikey, but you might find it cheaper/easier to get an assortment from a kit company or ebay. You can often get large assortments for less than $10US that will probably last you a very long time.Hope that helps.

author: JohnS_AZ
author_rank: Frequent Contributor
timestamp: August 19, 2010, 03:07:19 am
content: I agree with everything DJPhil said.Here's a WIKI that will probably give you way more info than you wanted to know/http://en.wikipedia.org/wiki/LED_circuitAlso, here's a mail order outfit I've had really good luck with. They have a 100 piece LED assortment for just a few bucks"http://www.goldmine-elec-products.com/prodinfo.asp?number=G8063Heck, if you're around Phoenix Arizona, I'll give you a fist full.John

author: DJPhil
author_rank: Frequent Contributor
timestamp: August 19, 2010, 03:26:38 am
content: Quote from: JohnS_AZ on August 19, 2010, 03:07:19 amThey've got all sorts of awesome goodies here: missile gyros, Geiger tubes, Ultraperm shielding sheets, IC die material that didn't pass QA, drill bits, etc.Great fun just to browse. These are the sorts of sites that keep me broke.

author: JohnS_AZ
author_rank: Frequent Contributor
timestamp: August 19, 2010, 03:32:27 am
content: QuoteSame here.Actually, eBay keeps me 'broker'.

author: EEVblog
author_rank: Unknown
timestamp: August 19, 2010, 12:39:14 pm
content: I concur with DJPhil also.Almost all LED's will be rated up at least 20mA or so.In fact 20mA is kind of a defacto-standard current, but most LEDs run easily at lower currents, normally under 10mA is much more sensible. Light output is almost linearly proportional with current, so 10mA half as bright as 20mA etc.LEDs don't have an "operating voltage", they are current driven devices. You pass a current through them to light them up.Yes, they "drop" a particular voltage when you pass a current through them, but they are not "voltage driven" devices. A common beginner misconception.Hobby electronic places like Jaycar and Sparkfun offer bags of "mixed" LEDs, they are what you need here.http://www.sparkfun.com/commerce/product_info.php?products_id=9881Dave.

author: baljemmett
author_rank: Unknown
timestamp: August 19, 2010, 01:44:09 pm
content: Quote from: EEVblog on August 19, 2010, 12:39:14 pmForgive me for a little bit of a tangent, but that was one of the things that suddenly 'clicked' for me and set me on the road to understanding the circuits I was building. I mean, I knew the fundamental laws (those of Ohm, Kirchoff, etc.) and the basic function of most components, but it wasn't until someone quoted the formula for calculating the current-limiting resistor for an LED at me in response to a mistake that I suddenly realised the interesting stuff was happening at a layer above the basic functions of the bits that get soldered down. If that makes sense...... the other big ones were looking at some of Flylogic's IC teardowns and suddenly 'getting' pull-up/pull-down resistors, and working through an infra-red repeating amplifier I'd built from a schematic trying to figure out why it wasn't working. That required working out what sort of signal I should be seeing at each likely point in the circuit, and understanding why the signal would be the way it ought to be; a massive leap forward from just building someone from instructions in ignorance. I'm very glad that the IR emitter LEDs I was using had their cathode and anode leads reversed from the usual convention, otherwise I probably would never have traced the entire thing through before hunting down the LED datasheets in desperation.

author: orbiter
author_rank: Frequent Contributor
timestamp: August 19, 2010, 03:05:34 pm
content: I always get my LED's from Ebay. I can recommend the following seller and if you live in the UK you get free postage tooI get all mine from here and buy them in the hundreds...http://stores.ebay.co.uk/bright-components

author: safarir
author_rank: Regular Contributor
timestamp: August 19, 2010, 07:55:21 pm
content: Check for 5mm led on ebay, they are very cheap and you can get the color you want.

author: Joshua
author_rank: Regular Contributor
timestamp: August 20, 2010, 02:34:33 am
content: Thanks everybody for your replies.This has really cleared up alot of confusion for me. Also thanks for the links to the websites and such; this is just the kind of information I was trying to find. I was hoping to find stuff pretty cheap, but 100 LED's for $4.00 just blows my mindThanks again,PianoKid1994

author: bearman
author_rank: Regular Contributor
timestamp: August 22, 2010, 09:26:44 pm
content: One hint when buying LEDs. Make sure you get LEDs with at least 100 MCD brightness rating. My experieince has taught me if you buy these huge bargain LED deals you get a lot of LEDs but they are not very visible in farely brightly lit environments. They are usually under 10 MCD light output. It sucks when you have to get right on top of an LED indicator to tell if it is really on or not or it looks like its on but it is ambient light shining through it. Most of these bulk deals don't even list MCD brightness output. Stay away from those or ask if they know what the light output is. I have seen adds describing "super bright LEDs" then I look them up if mfg. part# is provided and they are 5 MCD. A super bright LED to me is like 5000 to 15,000MCD. 100 MCD or higher is a good indicator light level.Oh! I use diffused LEDs for any logic output and indicator lights . I use clear lens LEDs for displays and lighting effects.The other thing is this. If the LED is too bright at 20ma. current level for your app you can always increase the resistance and lower the current running through it to lower the light intensity to meet your needs. If your LED is too dim too start with you can only increase the current so much before they die or have a short life span.I learned the hard way. In fact just the other I built a simple 20ma current source for testing all the LEDs I collected over 25 years. I threw away tons because they were just garbage and I would not use them for any real applications as they are too dim or not evenly lit and not very visible when on.Hope I saved you some grief and coinage.Bearman

author: Zero999
author_rank: Super Contributor
timestamp: August 29, 2010, 09:29:23 am
content: Also, don't neglect the viewing angle, you can get a narrow beam LED which is very bright but will appear dim if viewed from the wrong angle.

author: Joshua
author_rank: Regular Contributor
timestamp: September 03, 2010, 02:35:42 am
content: Quote from: bearman on August 22, 2010, 09:26:44 pmThanks for the great info! I've never heard of such a thing as MCD. I was actually planning onpossiblybuying such a bulk (discount) pack, but I think i'll just go straight for buying just quite a few of a specific kind.Quote from: Hero999 on August 29, 2010, 09:29:23 amThanks, I would have never thought of that.Thanks again everybody,Pianokid1994