99p LED Nightlight

A mains powered plug in light which illuminates at night only. The first video examines the device in detail including the circuit layout.

The Video

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This is a cheap (£0.99) night light which plugs directly into a BS1363 mains outlet. It has a light sensor on the front, and when dark the LEDs inside will illuminate.

The light is actually rather bright, certainly far brighter than the incandescent lamp version which the plastic case of this is based on. The plug pins are not level, but are so poorly made that they can easily be bent back into shape. The casing is fixed together with three screws, two of which are a 'security' triangular shape.


Circuit schematic for a 99p LED nightlightThe circuit is rather odd, in that the LEDs are connected directly across the supply, and to turn them off, a transistor is used in parallel with the LEDs, and when the light level rises, the transistor turns on and current flows via the transistor rather than the LEDs. This means the circuit uses a similar amount of power all the time, regardless of the LEDs being on or off.
It does at least have a fuse, although this is non-replaecable.

The AC supply is half rectified using a single diode, so the LEDs do have visible flicker.

Testing Video

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Current and Temperature

In the second video the current and temperature are measured. At a supply voltage of 250V, current is about 5.8mA with the LEDs off, and 5.7mA with the LEDs on. This is just under the 1.5W claimed on the packaging of the device. Most of the power consumption is heating the two 12k resistors, the LEDs use a tiny amount.

The resistors reach a temperature of around 110C, which is hot enough to discolour and partially melt some plastics. The LEDs are located directly above the reistors, so they will be subjected to excess heating as well, probably shortening their life considerably.