HOW TO CONNECT A SERIES OF LEDS

It depends. Parallel is good if you can use a series resistor with each LED to limit the current. It's good because one can burn out - short or open circuit, and the rest are still good.

Series is good if you have a high voltage source. But if one opens, you lose the whole string. If several short, you run the risk of burning up the rest.

We made a very bright ring light using about 100 LEDs. We put them in several series strings, and ran the strings in parallel. We used a driver chip especially made for LEDs with a current sense feedback.

At home, I replaced the incandescent bulb in my bike lamp with 5 (high intensity) LEDs in parallel. Their forward voltage is about 3.6V, so I was able to connect them directly to the 2 series "C" batteries without any resistor, running them at slightly less than full power.

Hi bhankiii- as someone who has experimented extensively with white leds since they came on the market here, around 2,000, I can tell you they a current limited device- not voltage limited(within reason)- this means that each led has a maximum current rating- exceed this & led life is short!. The exception is if using pulsed drive- I have driven 30mA leds at 130mA at 880kHz at 2.4v for similiar light output to 75mA led at 4v- the killer here is the energy taken by the driver circuit- about twice as the led uses- the most efficient is a series dropping resistor- in your case, obviously, the voltage/current is dropped by the wiring to the leds- or even dirty battery contacts- I have had leds burn out simply by changing batteries to a different type(eg, using NiCd,s as NiMH original, as NiCd,s deliver more current). Cheers.

Bhankii, you can avoid the disadvantage of a dead chain because of one burnt LED in a serial configuration by putting zener diodes parallel to the LEDs. The Zeners Breakdown voltage is selected slightly higher than the LEDs forward voltage. In case of a fail the burnt LED can be identified immediately.
Regards Uwe

I made a small 12 Led project using a parallel circuit, 15mA per Led. See my blog and video here--- AfaraWayland

Hi, where can I read part II?

its coming, probably Sunday. Thanks for the interest!

Part Two posted.