Easy and Cheap

Simple LED Tester

9 volt battery and a 470 Ohm resistor should do it...

Regards,

Or

if you don't want to roll your own, Ngineering has a neat tester that goes a bit further, allowing you to test the affect of different resistors with it.  I own this one and found it quite useful on a few occasions.

I second Kevins suggestion. I

I second Kevins suggestion. I use a very similar set up ( I use a 1k resistor). I have had  a similar experience as you. Even found a few amber ones..lol. I kept them, and did find a use for them.. ya never know..lol

Yes really...

A resistor somewhere between 390 and 1.5K Ohms will likely work well enough for testing.

The box Dave suggests may be handy if you are trying to choose a resistor value to get a certain look from a specific LED but if all you need is to test for operation or color this way works fine and is fast, cheap and easy.

I built my own using a 3 - AAA battery compartment from an old R/C toy, I cut it away from the plastic chassis with my dremel tool.  A resistor, some wire, heat shrink and a molex plug, finished it off.  It outputs 2.8 V @18mA and so far has worked to test red, green and white LED's just fine.

Edit: Recently I made a break out cable for my LED tester to aid in testing SMD LEDs.

Regards,

CR2032 large button battery

I have a battery holder with

I have a battery holder with two AA batteries wired in series. This is connected to two wire leads with alligator clips. No resistor needed if testing "white" LEDs. No good for yellow, green or red LEDs though.

Mark.

I buy the bulk warm white

I buy the bulk warm white LEDs from those ebay sellers in China for dirt cheap, and there are some color variations within the bulk pack. I assume they are seconds since they are so cheap.

I made up a bread-board with a dozen resistors so I can plug in a dozen LEDs at a time and connect it to my old DC throttle. This way, I can see the color of a dozen at a time and pick and choose quickly which ones have the right color. Hard to match colors one at a time.

Mark.

Those helpful ISE guys…

…might have a good suggestion. I think you know them.

Thank you

Thanks everyone for the tips!  I liked the simplicity of the 9v battery solution and had everything but the socket on hand, so I went that route.  Since my LEDs were all pre-wired, I went without the socket and just added a 1000ohm resistor.  I also soldered an LED permanently to the leads so I have an easy reference point when testing.  Works great, and I've now tested all remaining LEDs I had on hand.

Someone actually suggested a 9v battery solution to me a few weeks ago, but I thought it seemed more complicated than it really was, didn't understand the importance of testing before installation, and just generally was in too big of a hurry.  Unfortunately, once I wised up, I could no longer find that email.  If you are that person, thank you!  If I'd taken your advice, I wouldn't be in the position now of having to remove LEDs that are already installed.

Great to hear...

Regards,

@Joe

 "If you are that person, thank you!"....  I remember the email Joe. I still have it in my 'sent' folder..do you need it resent?  j/k..lol Glad to see it working out

Bulk SMD LED

Given the price of these is so cheap from China, I usually get them in 100 SMD rolls.  I buy "warm White" 0603 and have not been disappointed yet in either the color or the quality.  As Yaron mentioned, a CR2032 battery is perfect for testing LEDs.  White ones usually have a forward voltage of 3.2V +/- and this battery is rated a 3V.

I would expect to get a few that are not spot on, colorwise so I test everyone after I assemble it.

Tony!

Ack!  I should have remembered that Tony.  Found your email!  In the folder titled "Ditch lights", of all places.   I don't know why it didn't come up when I was searching for emails with the word "battery" in them the other day.  But thank you again!

As long as were discussing LEDs & Resistors

As long is we're in the neighborhood - the question about "what size resistor" is often asked.  Digi-key (among others) has a number of handy calculators online here.  These are also available in the Digi-key smartphone app.

Adafruit has a similar app called " Circuit Playground."

Another useful tool is the iCircuit circuit simulator. 

Overkill for the original poster's intention, but you may find them useful. It's been a while since I downloaded any of them, but I think they are all still free.

gs

Calculating the correct resistor value fo an LED

All LED's have a data sheet for them.  It will list typical intensity at the normal full working current, and the forward voltage drop.  Subtract the forward voltage from your supply voltage, and divide the remaining voltage by the current.  This will give you the correct resistance.  If you are running several LED's in series, add up all of the forward voltage drops, and follow the above procedure.

Example: I have two red LED's that I want to drive with 20 mA (milliamperes).  The data sheet shows the minimum forward drop is 1.8 Volts, and I am using a 12 V power supply. 1.8V+1.8V=3.6V  12V - 3.6V = 8.4V.   8.4V / .02A = 420 Ohms.  This is a non-standard value so I choose the next higher value which is 430 Ohms.  The power dissipation is .02A *.02A * 430 Ohms = 172 milliWatts, so any resistor power rating greater than 1/4W will work.

What most people do not seem

What most people do not seem to understand about LEDs is that the resistor is to restrict the current through the LED rather than to reduce the voltage. Yes, the LED needs about 2 volts across it to light up, but it will then pass as much current as is available to it at that voltage. By placing a battery directly across the terminals, you are relying on any internal resistance within the battery to restrict the current. If you manage to find a 3 volt battery with very low internal resistance, then the LED could take a very high current, until it breaks.

Ian

Hampshire UK

led tester

Something like this may be what you want

I forgot what it cost But i found a more modern version on ebay for less than US$15.00

 

John

All LED's have a data sheet

All LED's have a data sheet for them.

That may be so, but the data sheets aren't always included in the shipment. Maybe I have a unique skill of buying from vendors who don't supply the data sheets.

DrJolS

That's not how I understand current

That's not how I understand current vs voltage. Voltage is an all or nothing thing - a device will take it all, but current is a reservoir and a device will only draw what it needs from that reservoir. For example, if I have a 12V 5A power supply, some device on that circuit gets the full 12V but it will only draw the amps it needs, not the full 5 amps. A battery with a high amps reservoir will be no problem -- the LED will only draw the amps it needs.

Where amps becomes a limiting factor is on the upper end ... if a device needs MORE amps than the supply can provide, that can damage the supply, not the device. Too many volts can damage the device, not the supply. Too little volts in the supply doesn't hurt anything, the device simply won't work if it doesn't get enough volts. Too many amps in the supply isn't a problem because the device only draws what it needs.

At least that's how I understand volts vs amps.

Confusion - OUCH!

Joef,

I wish you had used a different word.

current is a potential 

Voltage is a measure of electromotive potential. Using that word to apply to current is confusing. I think (!) I understand what you're saying, but couldn't you have used a different word? Something like reserve or reservoir.

DrJolS

Joef NOTE: Okay, done. Reservoir it is -- edited my post to make that change.

That's lots better. Thank you.

DrJolS

Semiconductors are different

Semiconductors don't follow Ohm's law. That's why they are only semi-conductors. Once the forward voltage drop is established, they conduct vigorously. They will pass any current available, even if it generates enough heat to destroy the device. That's why we must take steps to control the current, usually with a resistor.

Incidentally, I don't bother to subtract the forward voltage drop from the supply voltage when choosing resistors for LEDs. The math is simpler, and it provides a safety margin. Since neither LEDs or resistors are that precise, I prefer reliability over getting every last bit of light.

pqe