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Applications & Solutions : What’s the Difference Between Astronomic and Daylight Saving Time settings on an Electronic Timer? 

Applications, Energy Efficiency

What’s the Difference Between Astronomic and Daylight Saving Time settings on an Electronic Timer? 

Electronic Timer

Whether using an in-wall time switch or a 365-day programmable digital electronic controller, timers with both astronomic and Daylight Saving Time (DST) functionality automatically adjust to the seasonal day-to-night time changes throughout the year. An electronic timer with astronomic functionality determines each day’s sunrise and sunset times based on geographic location, while the automatic DST functionality resets the clock by one hour in the spring and fall. This type of scheduling adaptability takes the hassle out of manually turning lights ON and OFF, freeing up maintenance staff for other jobs and enhancing a property’s safety. Understanding the terminology and programming capabilities makes specific scheduling of lights, signs, bells and other loads effortless and energy efficient. 

Location, location, location

First, what exactly does “astronomic functionality” mean? Astronomic is a fancy word for the methodology used to calculate the sun’s daily rise and set times based on a specific geographical location and the Earth’s rotation. 
The sun sets faster the closer the location to the equator. In the tropics, the sun dips quickly below the horizon, making for a very short twilight. As you move toward the Earth’s poles, the sun lingers along the horizon and twilight lasts longer and longer. This makes adaptive scheduling particularly important for proper nighttime illumination in places further away from the equator. 
Astronomic timers are location dependent. From a user’s standpoint, the timer needs to know its location in order to function properly. Some clocks can be programmed using specific GPS latitude and longitude coordinates; others will allow approximate parameters by simply selecting the country, state or province, and closest major metropolitan area. 

How does Daylight Saving Time affect an astronomical timer? 

When it comes to DST and time switches, a widely heard complaint is that having to manually adjust clocks when it’s “fall back” and “spring ahead” is a total productivity killer for maintenance staff. Here are a few tips on how timers with an automatic Daylight Saving Time adjustment can help free a team from the time change burden: 
1. Timers can be customized to a specific location with an ENABLE or DISABLE feature for DST. When enabled in locations that observe DST, the time clock will automatically change in the fall and spring. 
2. If a timer or controller has an automatic DST feature, but doesn’t switch to the correct time on the correct date, chances are the switch was installed prior to 2007. The Energy Policy Act of 2005 established new dates that began in 2007, changing DST to begin on the second Sunday in March and end on the first Sunday in November. Pre-2007 models of timers and controllers may have the automatic Daylight Saving Time adjustment; however, they were factory programmed to meet the DST legislation at that time. Since those dates have changed since then, correct local time will need to be manually adjusted by an hour each spring and fall. 
3. DST and astronomic functionality operate independently of each other in a switch or controller. For a clock to work properly, it needs to know its location, the local time, and whether DST applies to local time or not. If DST isn’t enabled on the timer, scheduled ON and OFF times will be off by an hour. 

Set it and forget it

With both astronomic and automatic DST functionality, a “set it once and forget about it” implementation can provide all types of properties with the energy-saving benefits of electronic programmable timers, from convenient stores and school districts to small commercial properties and residences.  
• The owner of a 24/7 gas station/convenience store in Mexico City uses the astronomic feature on an electronic timer for dependable ON at dusk and OFF at dawn control of outdoor lights and signage. Mexico’s “sunny again today” weather ensures the schedule varies by only a few minutes each day. 

• The wide range of sunrise times – from 4:20 a.m. in summer to 10:13 a.m. in winter – allows a homeowner in Anchorage, Alaska to take advantage of set it once and forget about it programming in an in-wall timer.  

• Southern California’s notorious June Gloom prompted a commercial property manager to create a customized program so the lights stay on one additional hour after sunrise to account for frequently foggy mornings. 

Another important benefit of astronomical timers is their customizability. Fixed ON and OFF events specific to a facility’s or property’s uses and events are just as easy to program as the SUNRISE/SUNSET schedules. This allows a system or load to stay on longer on the weekends or a specific night of the week, or turn OFF earlier than dawn. 
The programmability features and scheduling flexibility found in astronomic time switches and digital controllers help maximize energy efficiency and safety and minimize maintenance. Watch Intermatic’s how to videos to see how easy it is to set schedules for sunrise, sunset, or a fixed OFF, and ENABLE or DISABLE DST. 

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