Last winter we received the following question:
We have an enclosed wall mounted fixture for a security light at the side door of our house. The light is on all night. Our problem is getting the right light bulbs for the fixture. Standard 75 watt bulbs seem to have a very short life of just several weeks. We get below freezing temperatures on many nights during winter. Do you have any suggestions for a bulb we could use that has a longer life?
The first part of the answer is to note that incandescent 75 watt light bulbs (along with 100W, 60W and 40W) have been phased out. You may be able to find a few still in stock at some stores, but eventually, you will have no choice but to look for an alternative.
The advantage of CFL is its energy efficiency and relatively low cost. A screw base 18 watt CFL produces the same light as a 75 watt incandescent. It will cost $4 to $5 but will last 10 times longer than the 75 watt incandescent. Because of the cold climate, you can’t just buy any CFL and put it in a fixture that gets below freezing in winter. If you do, the bulb may not come on below a certain temperature. The fix requires that you read the specifications on the box. Look for a minimum start temperature. Some CFLs will start down to 32 degrees F, others down to 0 degrees F and some will start when the temperature gets many degrees below zero. If you don’t see information on minimum start temperature, keep looking until you do. Low temperature rated CFLs work great in cold conditions, particularly for this application.
The advantage of LED is the extra long life, and, they all have no problem coming on in very cold temperatures. In fact, LEDs get more efficient as the ambient temperature gets lower. A 14 watt LED is equivalent to a 75 watt incandescent, so there is a 4 watt advantage in energy efficiency compared to CFL. Where CFL has the big advantage is cost. The 75 watt equivalent LED bulb will cost at least 4 to 5 times as much as the CFL bulb. You should get 25,000 hours of life from the LED which looks great compared to incandescent but not as great compared to CFL, especially given the cost difference. Heat build-up in the enclosed fixture, especially on summer nights, could also lower the expected life even though the fixture is outside. LEDs require air flow around the bulb to remove heat from the fins or heat sink. With an enclosed fixture, you will not get air movement to pull heat away from the critical solid-state components inside the bulb.
For this application, we recommended the CFL option. The appearance of fluorescent illumination, which some people don’t like, is probably not a concern for a security light. The lower initial cost, good energy efficiency and, assuming a low minimum start temperature bulb is used, a relatively long life, suggest a good match for a home or small commercial outdoor security installation.
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