# Modify a Normal Study Lamp to LED Powered Lamp

I have an old study lamp, but due to the internal circuit problem (I suspect), its hard to turn it on, even after I changed the new tube. So, I decide to modify it to be LED powered lamp.

First thing I do is to “open” the whole thing.

I am not sure about the brightness of LED, but I will try to fit in 30 pcs white LED to the lamp. I arrange the LEDs in 3X10 array on a strip board.

Make sure that the 3X10 array do fit in the lamp.

Then, cut the strip board out, and solder the LEDs to the strip board.

I add in a electrolytic capacitor and resistor array to the board. You can actually use a higher watt resistor, but since I don’t have higher watt resistor in my component box, so, I simply parallel 12 pcs 220Ohm resistor to get 18.33Ohm, 3Watt resistor.

For the power supply of this lamp, I am using the 12V 1A AC to DC adaptor.

The complete schematic of the LED lamp. (click on the image to view larger size) So, the whole schematic is quite simple, the LED array at the left side will need more than 9V (forward voltage) to power up the LEDs (series of 3 set of 10pcs parallel LEDs), and the function of the resistor array is to limit the current of the LED to around 20mA each.

Then, I apply double sided tape to fit the board to the lamp.

Continue with the wiring of the whole lamp.

Complete LED powered study lamp.

I am quite satisfy with the new table lamp, at least I don’t have to wait for it to be started up. But, seems like I have over estimate the brightness of LED, or maybe the resistor that limit the current can be adjust(using smaller Ohm resistor) to make the LED brighter. Anyway, I will try it tonight to see the result in dark.

### 7 Responses

1. jay says:

Leds are current controlled devices not voltage. so the usual way to use them in your circuit would be a string of three leds in series with its own current limiting resistor of say 180 ohms. putting them in parallel means the led with the lowest voltage takes the most current. a small change in voltage of a led produces a big change in current. hope this helps.

Thanks a lot for the suggestion.

3. jay says:

Just found this site it designs the circuit for you.

Regards

Jay

4. satpathi says:

what is the value of Capacitor?