hey guys

i have a regular LED (30 mA, 3.6 v) and im trying to get the max bright and of course with max efficiency (less heat) so i connected it with a 4.5 volt (3 AA battery) and got the best of it but when i used the 9v battery i got the same glow but the much more heat in the LED so that got me thinking how much can the LED live on a 9v battery and a 4.5 net battery and is it ok to use the 9v keeping in mind that the whole circuit is just the LED

thanks

 

as long as you have a resistor it should be ok but you really dont need all that power so you need to figure out the max rating with what resistor you need

 

limit current to whatever LED is rated for and you can use any voltage...

 

Hello,

Always use a resistor to limit the current.
You can calculate it using the following formula:
Rlimit = (Vsupply - (number of leds * Voltage of leds))/wanted current
For example:
Vsupply: 9 Volts
Number of leds: 2 (in series)
Voltage of leds: 3.6 Volts
Wanted current: 20 mA
Rlimit = (9 - (2 * 3.6)) / 0.02 = (9 - 7.2) / 0.02 = 1.8 /0.02 = 90 Ohms.
Choose the next higher value to have a safe (lower) current.
The next higher value in E24 is 91 Ohms.
The next higher value in E12 is 100 Ohms.

Bertus

 

thanks very much that was more than helpful but one thing left :

you said "wanted current" so dose that mean i can supply any current below the max forward current (in my case 30 mA) ?

and if i do would it effect the brightness of the LED

thanks

 

Hello,

The brightness VS current is dependend on the type of led:


Relative Luminous Intensity vs
Forward Current
Ultra Red 4, HE Red 6, Orange 7, Yellow 8, HE Green 9
Red 5, Bright Red 3, Pure Blue C

This graph comes from this page:
http://www.theledlight.com/technical3.html

Wich is a page from this EDUCYPEDIA page:
http://educypedia.karadimov.info/electronics/composemiconductorsled.htm


Bertus



​

 

didfferent LED's have different micro candls MCD. 1000mcd is 1candle.
correct me if im wrong

 

Hello,

The luminous intensity will be given in mili candela.
See this page of the wiki for more info:
http://en.wikipedia.org/wiki/Candela

Bertus

 

When we using a LED, always focus on the current, because the voltage is almost constant, but the current is adjustable from 0 to Imax, as your LED current is 30mA.

When I using the LED, always set the current around or below 80% of LED, but almost use it below 80%, when we add about 70% of the Imax current to the LED, almost reach to the high brightness, if we using it over 70% of Imax, it won't increase much brightness, but if we add it over 80% to 100%, it will reduce the LED life, it will also reduce the Luminous efficacy of LED.

For example :
Your LED current is 30mA.
30mA x 80% = 24 mA, when you using your LED below 24mA, you will keep it safely for a long time.