Newbie question about resistance

I am trying to make a strip light for work in tight areas. I was planning on using 15 5mm leds. When I use the LED Pro and
insert the numbers the resistance = 32.22 when the leds are paralleled. Does this mean I need 1 resistor = to 32.22 or 1 resistor for each led?

Welcome-
I'm pretty new here too, but I've been putting 5mm leds in things for a year and a half now. I'd love to help you out, so can you please give me a little more info:

What is your source voltage?
Do you know the forwarding voltage of the leds?
(Are all these leds the same?)
How much power can your resistors handle? (cheap little ones usually are 1/4 watt)

I've put a bunch of 5mm leds in parallel, and have had a lot of fun-- so please answer those questions and I (and probably more of these wonderful people) will help you keep your leds running properly.

Michael

i recommend putting as many in series as possible.. but 15 in series being maybe as much as 40V or more might not be practical.... a driver that maintains constant current is a good plan.

this kind of light can be made with only resistors, but more info is needed.

identical LEDs is important for parallel design.. in-general.. resistor is needed for each branch.. i.e. you can have 3 branches of 5 LEDs or 5 branches of 3.. having groups in series will help even power distribution... a series resistance in each branch helps level each group, and each led in each branch will get the exact same current... it's a little tricky to have parallel and series in a long string, but it just means you have a set of parallel wires, but say 5 leds are wired in series with one resistor between the two wires, repeat as necessary.

-awr

If you entered one LED in your calculations then it is ONE resistor/per LED.... if you entered 15 LEDs in your calculation then it is ONE resistor for the 15 LEDs.
Take care to remember to use a resistor of proper power rating or you may overheat it, It may be cheaper to group LEDs in clusters of 3 or 5 if you find you may need to use resistors greater than the cheaper 1/4 watt versions.

at times it may be easier to make series/parallel circuits when you have a voltage greater than 7 or 10.5 volts available for use, this would make for less power the resistor(s) have to drop and less your transformer has to put out.

If you are using a transformer/power supply beware some float higher than their rating and sag when a load is put upon them. I have found it easier to put a large variable resistor inline with LEDs and an ammeter and crank it till I get the current output to the LEDs I want then measure the variable resistor and use that value for my fixed resistance source, this eliminates variables unaccounted for that creep up in calculations of components not meeting specs they are supposed to have.

Thanks for all the replies guys. I ordered all of them from superbrightleds.com so I hope that they are all the same leds. The Fv is 30ma and 3.5v, I wanted to use 1 or 2 9v batteries to keep things simple. Most likely I will be using a 1/4 watt resistor

If I wire the leds in clusters, how do I figure out the resisatnce needed?\

If you are using 9v as a driving voltage I would wire pairs of series LEDs in parallel which would require 16 LEDs or a a single one wired alone.... 18v driving voltage would be nearly ideal for 5 LEDs in series if the batteries didn't start considerably above that is would mean 3.6v per LED, you could try a pair off of 18v with a variable resistor and crank it till you get the current you require. Depending one what the capacity of your batteries is and their internal resistance you could find hooking them up to batteries like 9v transistor (rectangular cells) they may sag the voltage down a little which could throw off all your calculations.