Thread: Led Help

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No--100k means 100,000 ohms. The group of resistors you listed that you bought on ebay include some resistors labeled "100". Those would be the 100 ohm resistors.
I normally make circuits of two LEDs in series and pretty much exclusively use one 330 ohm 1/4 watt resistor in all of them, no matter what the color.
I haven't had much luck with the parallel circuits (yet).

and do they get put together just like the picture 2 leds then 2 resistors then 2 more leds or what

Originally Posted by DaveintheGrave

No--100k means 100,000 ohms. The group of resistors you listed that you bought on ebay include some resistors labeled "100". Those would be the 100 ohm resistors.
I normally make circuits of two LEDs in series and pretty much exclusively use one 330 ohm 1/4 watt resistor in all of them, no matter what the color.
I haven't had much luck with the parallel circuits (yet).

But dont you have to have a certain resistor to bring the voltege of the battery down to the right level so they are getting enough but not too much?

In putting together so many LED circuits I found that the 330 ohm seemed to work fine for most of the LEDs I was using. (I get most of my LEDs from Allelectronics.com.) The diffused green, diffused red, bipolar red/green, UV Blacklight, clear red and clear green LEDs all work fine with the 330 ohm. If the resistance is too much, the LEDs will be dim. If the resistance is not enough, the LEDs will get HOT very quick.
The way I solder the series circuit together is: Positive Battery wire--- LED---Resistor---LED---Switch---Negative battery wire.
I made some UV spotlights last year using 1/2 inch PVC connectors and pipe with a two-LED series circuit mounted inside.

So how many LEDs did you get for $9? I was cunfused by the description.

umm i think it was more like 18$ because the 9 was in pounds there were 100 leds for 18 or so dollers with shipping i believe. I got them today and started playing with them i have no idea what im doing i solderd 3 together and hooked it up to the battery and they blinked and went off and never lit back up then i took four leds and a 100ohm resister and they light up great they were worth the money

100 for 18 bucks! That sound like a great buy. I should look into getting some. I have been wanting to add som LEDs to some props.
Thanks,
Jim

Looking at the diagram you provided, we'll call each set of 2 LEDs and a resistor a "string". So, you will have two "strings" in your spotlight. It really doesn't matter where you put the resistor in each string - just make sure each string has 2 LEDs and a resistor. DaveintheGrave puts his resistor between the LEDs, I put mine in front of the first one, the diagram puts it after the last LED.

A little in-depth info:
Each string, by itself, is called "wired in series" because the (-) lead of the first LED is connected to the (+) lead (or either end of a resistor) of the other, then looped back to the negative battery wire. Now, because both strings are connected to the (+) battery wire (as a "Y"), then both other ends are connected to the (-) battery wire, they are "wired in parallel". So, you'll have two series strings wired in parallel. Cool, huh?

Originally Posted by Voodoo

100 for 18 bucks! That sound like a great buy. I should look into getting some. I have been wanting to add som LEDs to some props.
Thanks,
Jim

Yup and the only draw back if you want to call it that is it comes from Hong Kong and it takes 7-10 days to get here but price wise well worth the wait

Why am I always drawn to these LED discussions...

First off, welcome to the 21st century of lighting. Like everything else new and improved, it is also more complicated.

First off - LED purchasing. NOT ALL LEDs ARE CREATED EQUAL!!!! If you are not concerned about the color or beam-pattern of your leds, Ebay is the place to get them. However, if you are looking for a good even beam across the visible emmision angle, you're going to have to pay for them. By far, the leader in performace and quality in T1 LEDs is NICHIA. They are more expensive, but may be worth the price in the long-run due to consistent beam patterns and better color rendering. If POWER is what you are looking for, LUXEON leds are the all-out champion - but they have drawbacks as well.

LEDs are (usually) rated in mcd (millicandela). This rating represents the amount of light the LED produces within it's rated angle. Unlike incandescent lights, LEDs only project the light within a certain angle (like a flashlight). The tighter the angle, usually the higher the mcd rating. This does not necessaraly make the LED brighter than a lower mcd rated LED. It all depends on how you want to use it. If a spotlight is desired, then a small angle may be desireable, but large areas will require miltiple LEDs to give good over-all illumination.

Two groups of LEDs are rated in lumens (the same as incandescent lights). These are High-Flux LEDs (know as piranahs and super-flux) and LUXEON. These ratings represent the total amount of light produced in a 360 degree area. The two ratings can be converted to one-another using a formula, but here is the easy way to do it : http://led.linear1.org/lumen.wiz

Let's do a quick comparisons. The 5000 mcd 20 degree Red LEDs you purchased, convert to 0.477 lumens each. A LUXEON 1 watt red LED is rated at 42 lumens. Simple math tells us that it would take about 88 of those T1 LEDs to equal 1 of it's equivilent LUXEON.

The above comparison might seem like a hands-down endorcement for the LUXEON. However, it's not that simple. LUXEON LEDs require special handling. At 3.3v and 350ma, standard resistors may have problems with heat-buildup. Traditional voltage regulators will get uncomfortably hot driving even 1 LUXEON. Even the LEDs themselves can get hot and must have a heat-sink attached if being driven to their max. A simple solution to all of the above problems is to connect 4 in series and drive them with a standard 12 v outdoor lighting transformer. This will provide just under 3 volts to each LED, keeping the LEDs cool enough to touch, and eliminates the need for resisitors or voltage regulators. Other options include building specialized LED drivers (can get complicated) or purchase commercially available drivers (expensive!). For plug-and-play capability, an outdoor transformer can be re-wound to produce the desired voltage, but this can get dangerous and if not properly done can create a fire-hazard.

As of this post, LUXEON LEDs have dropped considerably in price. The white 1 watt LEDs I purchased 2 months ago for $6.95/each are now down to $3.59/each. The red 1 Watt I used as a comparison, is now down to $2.25/each (http:\\www.futureestore.com). At these prices, I find it hard to justify standard T1 LEDs any more. The added flexability more than compensates for their short-comings.

An added bonus, the LUXEON Star fits PERFECTLY inside a 1/2" PVC elbow. No cutting bottle-tops or creating special mounts. Just drop them in.

BTW: I do not work for or am in any way associated with Lumileds or Future Electronics. I just like the Lumileds products and feel they are an IDEAL match for our needs as home haunters. Now with the price drops, I believe more than ever that they are an affordable and preferable solution.