If your security light triggers at random then it may be detecting movement from the road, pathway or animals. 

There are a few tips to help solve this:

1. Change the PIR sensitivity- You can reduce the sensitivity of the PIR by turning the sensitivity dial anti-clockwise. This also helps avoid activation from small animals.You can find the dial next to the PIR sensor. 

Note: Not all models have this function.

2. Adjust the PIR position - You can tilt the PIR to adjust its detection area, this way it can be moved downwards to avoid the PIR detecting movement further away such as on a road or pathway or left and right to avoid a neighbors property.

Note: Not all models have this function.

3. Adjust the position of the item - Reducing the mounting height of the item will reduce its overall detection area, also moving the item away from sources of heat such as a boiler flue can help avoid random detection.