Reading Lamp Hack

The Reason:

I wanted a reading lamp that I could carry around my home lab when that extra bit of light was needed. This would also aid in making better mobile phone photographs for my blog.

Concerns:

• Should not be heavy
• Should have ample light
• Battery should last for 5~6 hours
• Battery should not have memory effect

Items used:

1 Watt Led 3.7 Volt + Heat sink + pcb 

1 Watt Led Driver

1 3.7 Volt Li-ion battery [2 batteries if you want twice the backup time]

Tools:

Soldering Iron

Screw Driver

Wire stripper

Insulation tape

Here is a quick video:

Instructions:

Choose an led driver that matches the output of your chosen led. The lithium ion batteries do not suffer from memory effect  so it can tolerate interrupted charging cycles. A 3.7 Volt Li-ion battery can be charged at a voltage of up to 4.2 volt. Led drive that I chose produces 3.8 volt and hence is within the safe limit and wont overcharge the battery. 

I had an old reading lamp stacked away in my store room which was just what I needed. This particular lamp had a 2 position switch for two brightness settings so I used a  100 ohm resister across one position. This is optional, so I didn't mention this in the items list. 

Putting the whole thing together is pretty straightforward and you can use your creativity here. Here is the general idea. I used the power chord and the switch that came along with the lamp because they were in perfect condition, removed the rest of the components including the AC bulb. Put in the led and wired it to the led driver through the switch. The lithium ion battery is connected in parallel to the output of the led driver. That is it....done...

Calculation:

1watt / 3.7 volt = .27 Amp

My Li-ion battery is rated at 1.8 AH [1800 mAh]

1.8 Ah / .27 Amp = 6.7 Hours

So one full charge should give me about 5~6 hours of light output at full brightness. With two Li-ion batteries you get up to 12 hours. The position through the 100 ohm resistor takes a fraction of this and should last the whole night even with one battery....a perfect night lamp :)

Here are some snaps: