External security lighting can be on for an average of 12 hours a day, 365 days per year. This is more than the average classroom light which is on for six hours a day, 190 days per year. As a result, replacing external lighting with LEDs can be very cost effective, particularly for the circular compact fluorescent D-type lighting. These bulbs are inefficient and pay back on your investment to replace them with a like-for-like bulb is less than a year. In most circumstances, you will not need to replace the fitting, just the bulb.