9 V battery = bad choice, low power.
Another choice, 12 white SM LED's in series, one 300 ohm R, 3 AA or 3 AAA alk. batteries, & boost converter.
3 AA's & boost need 7 X 5 X 1.5 cm. Adjust V output to desired brightness, about 5 mA?
I used this with a " holiday " hat, but only 4 LED's in series & 3 AAA's. Boost is size of 2 AA batteries side by side; might find smaller one to go with AAA's.

 

It may seem non intuitive, but super bright LEDs will illuminate at very low currents. I got one to be quite visible with only 250
ua (0.25ma). This also should allow you to use 3.3v as well. I got one to glow quite well with 10k @ 5v. I did not try 3.3K at 3.3v, but it should work.

 

It may seem non intuitive, but super bright LEDs will illuminate at very low currents. I got one to be quite visible with only 250
ua (0.25ma). This also should allow you to use 3.3v as well. I got one to glow quite well with 10k @ 5v. I did not try 3.3K at 3.3v, but it should work.

Well 3.3K, if that's what these resistors are (orange stripe, orange stripe, gold stripe, gold stripe), does not light up more than one white LED. I strung 4 white LED's in series (as in Tonyr1084's example) with one 3.3 resistor on the negative end. None of the LED's light up with 3volts from two AA batteries. One LED lights up if on it's own, with or without a resistor.

 

No, they need to be in parallel with each other with their own current limiting resistor.

3.3k is red red red, 33k would be red, red, orange.

The LEDs I used are here.

https://www.sparkfun.com/products/531

They are spec'd on the data sheet for a forward current of 20mA @ 3.2 to 3.4V.

There is nothing about their voltage to current curve below 3.2V.

I observed a lack of visible photons at 2.8V

I have 10 of them and all seem to be identical in specs.

They just start to illuminate at 2.5v, and need a minimum of 50uA to be visible. At 500 uA they are quite bright.

I used a current limiting resistor of 1k and got good results from 3.0v to 3.3v. (500 to 800 uA).

They would work quite well with 2 1.5v AAA cells and would have the added benefit of indicating weak batteries.

Total current draw for the 4 leds would be 2 to 3 ma.

 

...3.3k is red red red, 33k would be red, red, orange. ...

I bought 3.3Ohm resistors, it says 3.3 on the sticky label on the packet and the stripes on them are orange, orange, gold, gold.

I've given up with this. Just going to leave it as a clock without lights. Nothing works and your suggestions don't make any sense to me. I thought buying any LED's would suffice. I've already spent loads on various components I'm not going to use (and because you can't just buy one thing you have to buy multiples of them).

I'm not continuing, thanks for all your help anyway.

 

Sorry to hear. I made a mistake 3.3k would be orange, orange, red, not as stated.

 

Not given up yet. Just this final thing: https://www.dropbox.com/s/d3jp0pvwhifop50/12 LED in a circle.jpg?dl=0
Would that work?

The centre spindle of the HDD can act as a conductor for the positive. One wire in (positive) and one wire out (negative).

Please forgive the crudity of the image, I drew it in Paint.NET quickly.

 

Yes, the circuit should work, but the resistor values are way to low. What are the part numbers of the LED that you are considering? If you check out the specs of them and apply Ohm's Law, you should be able to come to a good value for the resistors. Using the LED's that I referenced, your resistor value would be 6.8K. (Blue, Grey, Red). (anything between 3.3k and 10k would probably be OK).

If you are using 'regular' LED's with operating currents of 20mA, your resistor values would be approx 470 ohms.

So your current draw will be between 0.25 AMPS, or 0.012 AMPS depending upon what LED technology you are using

 

Yes, the circuit should work, but the resistor values are way to low. What are the part numbers of the LED that you are considering? If you check out the specs of them and apply Ohm's Law, you should be able to come to a good value for the resistors. Using the LED's that I referenced, your resistor value would be 6.8K. (Blue, Grey, Red). (anything between 3.3k and 10k would probably be OK).

If you are using 'regular' LED's with operating currents of 20mA, your resistor values would be approx 470 ohms.

So your current draw will be between 0.25 AMPS, or 0.012 AMPS depending upon what LED technology you are using

I have these LED's: https://www.amazon.co.uk/gp/product/B00S7YY57U/ref=oh_aui_detailpage_o09_s00?ie=UTF8&psc=1
and I'm using just the 3mm white ones.

The resistors I don't have yet, I've only got 330K (orange, orange, yellow), 3.3 (orange, orange, gold).

I used this site: http://led.linear1.org/led.wiz
to calculate what resistors I need, based on 12 LED's at 3.2 forward voltage and 20mA forward current. It says I need 150Ohm at 1/4w.

 

I realize that the 'normal' operating point for these parts is 20mA at 3.2v.

This is fine if you intend to use the clock display as a high intensity reading lamp, but I suspect that you simply want a pleasant display that you may look at without over stressing your optic nerves.

If you just need to be able to see them illuminated at a comfortable level, their current needs are far lower. I think that you will find 1 to 2 ma quite sufficient. 3,300 ohms (3.3k) would be a good value to try.

A orange, orange, gold (0.33 ohm), resistor, provides no significant current limiting.

A 9v power source would instantly burn out the LEDs with only a 0.33 ohm current limiting resistor.

 

...A 9v power source would instantly burn out the LEDs with only a 0.33 ohm current limiting resistor.

That's weird then. I've tried 1 , 2 and 3 white LED's with one 0.33 (orange, orange, gold ) resistor and 9v and they did not burn out instantly. In fact I've lit them up for a while and they haven't burnt out. I've also tried just one white LED with a 330K resistor and it did not light up at all.

So with that diagram of the clock, do I go by what the resistor calculator says and use 6 150Ohm 1/4w resistors or something else?

EDIT

Oh and that's the other thing: Metal Film Resistors or Carbon Film Resistors? What's the difference (other than one being blue and the other beige)?

 

Thought I'd share with you all what I did in the end (see attached images).

 

They can also be glass/ceramic which you may get some light through. Try it and see.

I don't think so.