Little project I would like a little help with

[Crimmy]

Hi all,

I'm trying to make my girlfriend a nightlight for Christmas, and need a little help. It'll be battery operated, and based around 3 LED's. I want to use a battery holder I have that uses 6 AA batteries in series (9V). From my understanding, the most effective/efficient way of running this would be to run the LED's in series, is that correct? And can anyone give me any pointers of where to find an LED that has a recommended voltage of 3V?

Many thanks,

Crimmy

[Pauldf]

As long as they are identical you can use series, bog standard LEDs are usually 2v 20mA.
With 3 in series you'll need a 150ohm resistor in series which will drop 3v at 20mA.

[Crimmy]

Hi Pauldf,

Can you point me in the direction of where I can get LED's like this? I had a look and they all seemed to want voltages over 3.5V.

Many thanks,

Crimmy

[Pauldf]

Lots of places sell LEDs,
http://cpc.farnell.com/webapp/wcs/store ... =110155305
http://www.maplin.co.uk/c/components/leds-and-displays
The voltage and current vary for each one hence when you have decided on which LED you want you need to calculate the resistor needed.

[Crimmy]

But my confusion is that I have one of these lying around: http://www.maplin.co.uk/p/5mm-white-led-n28fn but its required voltage is 3.6V isnt it? So I cant power 3 of these with my 9V supply... unless I'm getting the wrong end of the stick and these will work at a lower voltage?

[David]

Current is correlated with both voltage and light output. As this is for a nightlight, I would expect you do not want it to bee too bright, so the LED may be OK at a lower than normal current. LEDs must always be used so that the maximum current cannot be exceeded, and the usual way is with a series resistor. A very useful calculator is to be found on this site (under the "resistance" tab).

IMO there is really no alternative to experiment in your application - try the LED with a variable resistance in series and adjust until you get the brightness you want.

[Crimmy]

So I can use the LED I linked with a voltage of 3V then?

[Pauldf]

Try it and see if it is bright enough