LED Lamp Modification

At my home I have a car port. In this car port there used to be Halogen lamps but I replaced them years ago by LED lamps. I have been using two flavors:

1. A LED panel with 9 or more LEDs on it.
2. A LED lamp that looks like a Halogen lamp.

I noticed that the LED lamp broke down more quickly than the LED panel. In case of the LED panel I also noticed that the brightness became less over the years.

The reason for these LED lamps or LED panels to break down more quickly is because of the temperature they reach during operation. Since I ran out of LED lamps, I ordered new LED panels with the idea to extend the lifetime of these LED panels.

You need the following supplies:

1. A LED panel using a PT4115 IC or equal
2. An SMD resistor of 0,82 Ohm

In the picture you see the LED lamp that I have been using the last years. Since I noticed that they broke down more quickly than I expected, I started measuring the lifetime. The lamp is automatically turned on when it gets dark. Since that differs during the year I assumed that the lamp is on average turned on for 12 hours per day. Here are some figures of this LED lamp:

1. Specification of lifetime: 30.000 hours
2. Estimation:
3. Lamp on-time about 12 hours/day
4. Lifetime should be around 2.500 days or 7 years
5. Measurement replacing 8 LED lamps over time:
6. Replaced on average 1 LED lamp each year
7. So actual lifetime is around 4.300 hours

This is much less than I expected so it was time for me to find a way to extend the life time but this time using a LED panel since you cannot modify the LED lamp.

I am using a LED panel as shown in the picture. This LED panel uses the standard application of the PT4115 IC as given in the data sheet.

The current through the LEDs is based on the value of Rs according to the following formula: I = 0,1/ Rs. The resistor can be found on the back of the LED panel as shown in the picture.

In the original version this is:

1. I = 0,1/ 0,56 Ohm = 179 mA
2. P = U * I = 12V * 0,179 = 2,1 W

In order to extend the lifetime I changed resistor Rs to 0,82 Ohm. You then get:

1. I = 0,1/ 0,82 Ohm = 122 mA
2. P = U * I = 12V * 0,122 = 1,5 W

Although this will reduce the brightness of the LED panel – which is hardly noticeable - it is still sufficient for my car port.

did some measurements before and after the modification and used a DC power supply of 12 Volt (the LED panel normally operates on 12 Volt AC). I measured the current but also the temperature at the back of the LED panel, so at the side of the resistor.

Before modification:

1. Current: 162 mA
2. Temperature: 55 degrees Celsius
3. Power: 2 Watt

After modification:

1. Current: 97 mA
2. Temperature: 40 degrees Celsius
3. Power: 1,2 Watt

With this modification I hope the lifetime will be extended but it will take some time – hopefully years - before I know how long that will be.

Keep you posted.