Hello. I am trying to put together a specialty lighting system that uses small 6 VDC lights. The wattage of each is 4 watts. What type / size of transformer will I need to power up to 80 of these lights? The system can be powered by more than one transformer, so if easier I can put in a tranformer every 10 or 20 lights? Thank you for any help you can give.

80 X 4 = 320 watts
320/6 =53.3 Amps

DC Lighting, Transformer? Isn't there a contradiction here?

The lamps can be placed in series parallel combinations.

120/6 = 20; so you can connect 20 bulbs in series and connect to 120 VAC like Christmas lights. 20* 4 W = 80 W per string.

For some reason, I was thinking he wanted to use 6 volt transformer.
Kiss's method would be better, since 120 volts would be available for transformer anyway.
You would not have redundancy, one bulb out on the string, will take the rest out.

Please explain more about this system, what is the purpose, where will it be installed, for example.

Datasheet on the lamp?

I doubt you will happy with a series system, one lamp burns out and all go out.

The Ohm's Law math does not lie, you will have a total amp load of 53 amps at 6 volts.

You will not be using a "transformer" for DC, more appropriately would be called a DC power supply, which will have a transformer AND a rectifier.

Since you will have 53 amp load, I suspect you will need several power supplies, as I cannot find a 6 volt DC PS that can handle that total load.

Your right TK, the Math does not lie, first results looked a little large, then I figured current of each and multiplied by 80 and it still comes up with the 53 Amps.

There is plenty of DC supplies in that range: AMETEK Programmable Power : DC Product Series

The series connected thing wouldn't be too bad, if you placed a monitoring lead say every 5 bulbs. You could at least detect a failure within 5 lamps. Twenty is a bit much.

The series thing could work with 4 strings of 20, and have each strings bulb be every 4th bulb, losing a string would not be as bright, you would have 75% brightness.