Book light improvement

rainyliveshere · Jul 12, 2026

Assalamu Alaikum and hello everyone. An electrical engineer and tech blogger here. About 3 weeks ago, I made this circuit to read books on bed in darkness. Actually, I wanted to use COB LED or ultra bright LED. But none was available in local online shops. Sourcing only one or two pieces internationally was not cost effective. So, a generic white 5 mm LED was my only option. So, I made the following.

This was the light output.

I was thinking about improving the circuit and structural design. I was looking for suggestions. But 2 days ago, I noticed that the light looks dimmer than before. I did not use the light every night. I only used it about 10 times. It is already dim. I'm not sure why. Is it due to a knock-off battery or the circuit itself has a problem? I know the common practice is to use a current limiting resistor but is it essential in case of a single coin cell battery too? Please share your thoughts. Thank you.

bertus · Jul 12, 2026

Hello,

Read this thread on aac;

https://forum.allaboutcircuits.com/threads/book-reading-led-light.210446/

It will give you info.

Bertus

rainyliveshere · Jul 12, 2026

bertus said:
Hello,

Read this thread on aac;

https://forum.allaboutcircuits.com/threads/book-reading-led-light.210446/
It will give you info.

Bertus

That AAC thread was created by me. That was created before I made my light. Later I posted the pics of my board in that thread. The current electronics lab thread is specifically about the dimming problem that I am currently seeing.

bertus · Jul 12, 2026

Hello,

The cr2032 has only a capacity of 225 mAh
Battery size 20 × 3.2 mm
Maximum discharge current: 3 mA.
Maximum pulse discharge current: 15 mA.

This is also the most common lithium cell. Commonly used on computer motherboards as nonvolatile BIOS memory and real-time clock (RTC) backup batteries, device remote controls, car FM transmitters, remote key fobs for cars and other vehicles. Also in other devices such as key finders like Apple's AirTag. Weighs around 2.9 g.[31]

More info on battery sizes: