I made a simple LED circuit using a battery, a variable resistor, and a LED. When the light intensity satisfied my demand (I do not need the full intensity) by changing the resistance, the condition was: R1 voltage: 0.5V LED1 voltage: 2.3V Current: 86 uA
Now, I want to add one more LED in a series to make a dual LED system. But I don't know how to calculate the appropriate supply voltage and resistor to keep the light intensity the same (= same current of 86 uA through 2 LEDs). For example, what should be the resistance if I use 4.5 or 6V supply? Any thoughts or suggestions?
LED: https://www.digikey.com/products/en?keywords=XPEBGR-L1-0000-00E02CT-ND
Okay, now I update a new circuit to supply 5.5V using a voltage regulator. It is battery powered (6V: 4 x 1.5V AA), so I want to keep the current (or voltage) constant ( ~ 86 uA) during the period of operation. Do you think this circuit would work as intended? (Let's ignore the product error between the same LEDs)
https://www.digikey.com/product-detail/en/ablic-u-s-a-inc/S-1133B55-U5T1U/1662-1276-1-ND/6601416
Or what about this design for the parallel arrangement?
I want to supply the constant voltage while the battery voltage goes down. That's why I need to use the voltage regulator.
Voltage regulator: https://www.digikey.com/product-detail/en/texas-instruments/LP3985IM5X-2.5-NOPB/LP3985IM5X-2.5-NOPBCT-ND/3527410