I'm messing about with LEDs and power supplies.

I'm not in the stage where I have any hardware. ( well I do have several low voltage lighting transformers left over from a renovation)

I'm still trying to figure out how to do what I want.

Take this:
R = (VS - VL) / I
where
R = the resistor
VS is the cumulative voltage demand of the LEDS in series
I = the LED draw in Millliamps (Ma)


For a series of 6 LEDs ( assume 2 VDC for each) I can take a 120VAC line voltage rectify it to DC and end up with :
120 - 6 / 0.02 = 5850 Ohms resistance
Does that make sense? I need a resister of 5850 Ohms??



Then on to the power supply.
I need no less than the voltage the LEDS will draw down.
So a 120 DC line will not drive more than 51 LEDs?
Does that make sense?
I can only drive 51 Two Volt LEDs on a 120 Volt supply line?

I've seen systems where way more than 50 LEDS are running in a plug and play bank of hundreds of LEDs and the thing is sold to plug into a 120 VAC line.

What am I doing wrong??

I'd started out wanting to use a single phase linear step down transformer and a bridge rectifier to get 12VDC.

Would I be better off starting out with a 120 VAC line, feeding a series of Step down transforms each of which was rectified to DC ?
The transformers I now have will yield 12Volts under load.

The reason for converting to DC is to not have the LEDs in the OFF mode for the period between 60 Hertz cycles. It adds up over time to a cumulative loss in light output.


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This is 72 white (2 volt) LEDs on a board
www.bgmicro.com/index.asp


The Description says:
This assembled and tested unit 72-880nm LEDs with a 50 degree viewing angle. The LEDs in this unit are capable of drawing 100mA. each. The Bigger IR ILLUMINATOR kit is designed to operate between 12 and 13.8Vdc, with maximum efficiency at 13.2Vdc. IR Illuminator draws between 600-800mA. Units can be daisy chained. At 24 feet, the beam is approximately 8 feet in diameter. PC board measures 3.7"x1.95".

They says it's tested with this
$4.00 power supply
www.bgmicro.com/index.asp

This is informing me that I am all wrong about power supply requirements.
Or is it ?
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Is this picture wrong?
I should have thought the Resistor would need to be on the + terminal of the LED and not the - terminal.

wolfstone.halloweenhost.com/Ligh...e.png

here:
www.theledlight.com/ledcircuits.html
They have the Resistor on the Positive terminal

What are the mechanics of why one would put the resistor on the Neg or Pos terminal?