Therefore, a lamp design with 7 LEOs making up a string of 7W is considered. So, 5 strings in parallel contribute to 35W.
Similarly, a 9W LED lamp is to be made using nine 1 W LEOs. These 9 LEOs can be connected in any way. But
each LED lamp has a forward voltage of 3.5 V.
For the lamp, it is assumed that 3 LEDs are connected in series. Hence, the
total voltage developed across it is, 3.5*3= 10.5 which is
approximated to 12V for safe working. Thus, in order to use
the LED lamp under optimal condition, it should draw a
current of 9112=0.75 A which is approximated to lAo Each
LED has a forward current of 350 rnA meaning, that is the
maximum current that can flow through it, for it to work
safely. Thus, this 1 A should be divided in such a way that
each parallel path should contain only 350m A. Or, the
number of parallel paths, is 1/350 m A = 2.85 which is
approximated to 3. Thus the 9W LED lamp has 3 parallel
paths each containing 3 LEDs in series. Such 4 LED lamps are
made.