[MOVED] LED constant brightness

[shubhangiagarwal]

an LED with maximum and minimum voltage drop of 1.8V and 3v respectively should be connected to which of the following to get constant brightness:
(a) 29V supply with 820ohm
(b)5V supply with 120 ohm

 

[betwixt]

Trick question?

The brightness will always be constant if the voltage and series resistance are also constant.

Brian.

 

[jeffrey samuel]

as long as the supply is capable of dissipating power equal to the rating of the LED it will have constant brightness

 

[HTA]

In this case it is the better to use a constant current, or driving it like a laser diode with monitor diode(would mean you need a photo transtistor for the feedback). This provides optical power control. Here are the LD principles: https://www.ichaus.biz/upload/pdf/EuroPhotonics_H89_2004_Driving_Diode_Lasers.pdf.

Enjoy your design work!