got a bunch of leds out of a music making toy i have red blue and light sesor leds (move yourhand over them and they turnsomething on)
i can hook a blue led to a usb cable fine lights up
when i try a red led i have to put a tiny resitoron it for it to work
does red take more power?
Comments
Have a look at http://en.wikipedia.org/wiki/LED#Colors_and_materials . It has info on voltages.
It depends on the voltage due to the current-voltage curve of a diode. Above a certain voltage a near infinite current can flow but below it, a small current can flow. Its also the reason why some small LED flash lights don't have limiting resistors. Also most LEDs dont have inbuilt resistors, the larger high power ones sometimes do though.
You can calculate the resistor value from this formula.
R=(Vs-Vl)/I
Where R=the resistance
Vs is the supply voltage
Vl is the led voltage
I is the led current
So if Vs=5v and Vl=2v (normal v for most led's) and I=10mA (common current for most led's)
then R=(5v-2v)/0.01A
so R=300 Ohms
For the blue led Vs=5, Vl=4, I=20mA (common for blue led's)
so R=(5v-4v)/0,02A
so R=50 Ohms
of course I'm guessing at the current of the led's but this will stop them burning out so quickly.