I noticed recently that about 80% of the units in the complex do NOT have their porch-lights turned on at night. This is no doubt because it costs money to leave lights on, so many of us turn off ANY lights we are not currently using. The problem is that when people are allowed to lurk in front of our homes in the dark, our neighborhood is not secure. Also, if you are coming home late at night and fumbling with keys, you and your home are vulnerable if there is no porch light on.
LEAVE THE PORCH LIGHT ON! For about 20% of our neighbors, their solution is just to leave their lights on at all times. The problem with this is that there is a cost. Assuming a 60 watt bulb (the maximum our old fixtures could use) and 730 hours a month, a bulb running all the time uses about 43.8 Kw (kilowatt hours) of energy (60 x 730 / 1000). In Arizona, it costs us about 7-10 cents per Kw depending on the time of day and the plan you are on (night-time is much lower on some plans). Assuming 10 cents, therefore, it costs us about $4.38 per month for the added security of leaving the lights on ALL of the time, not a bad investment in personal security.
SECURITY & ENERGY MINDED ALTERNATIVE: Many people in the community have one of the new porch light fixtures installed starting with the 2011 rehab, which has TWO significant benefits over the old fixture. First, the new fixture can handle 100 watt bulbs for increased porch security, and second, the new fixture has room to install photocell light sensor bulb adapter. By installing a 100 watt CFL bulb and a light sensor, we aren't wasting energy during the daylight hours and we are getting nearly twice the brightness as a 60 watt bulb for a third of the cost (100 watt CFL bulbs only use 23-26 watts). Assuming that the light is now on for only 300 hours in the summer and 400 in the winter, a 100 watt CFL bulb will cost between 60 and 80 cents per month to operate at night-time only.