Solar Timer

I wrote about a self-adjusting timer back in 2008, but only wound up buying one yesterday, once I realized they now worked with compact fluorescent bulbs, and after checking that I had a white neutral wire available in the switch box. I got the Defiant Daylight Adjusting Indoor Digital Timer from Home Depot (model no 49814, store sku is 469637, internet sku is 203678179, UPC code is 43180 49814). I installed it for my front porch light and set it to come on at sunset and to turn off at sunrise. The timer should adjust itself as the days get shorter, always coming on at that day’s sunset and turning off again at the appropriate time of sunrise. It doesn’t do this by sensing light, but by calculating the correct time of sunrise and sunset. But the only things I told the timer were that I lived in the southern third of the US, the current date and time, and today’s time of sunrise and sunset. With some other timers you actually enter the latitude and longitude. I wonder how accurate their approach will be?

Setting it up was kind of a pain. It has all kinds of different programs that can be run for weekends only, weekdays, every day, individual days, Monday-Wednesday-Friday, and Tuesday-Thursday. You can have it come on at specific times or dawn or dusk (others let you have an offset from dawn or dusk, but I think you can overcome this by just entering the offset as the dawn or dusk time; for instance if you want the light to come on at 30 minutes past sunset and sunset is 8:00, just tell it that sunset is 8:30). The 8 triangular buttons you use for setting the time or programs are hidden behind a cover the size of a postage stamp, so it isn’t easy to read what is written on the buttons at all. And the instructions are complicated enough that I’m not sure you could figure it out on your own.

Using the Star Walk app on my iPod, I entered the sunrise time today as 6:49 AM for Atlanta, GA, and the sunset as 8:40 PM. I will check back every now and then and see if it is adjusting like it should.

I’m not sure whether getting new plug-in timers is as compelling. I already have three electro-mechanical plug-in timers that I use to turn lamps on and off. They were cheap and they work fine except they don’t correct for varying lengths of days (so I make adjustments every now and then by turning the dial) and if there is a power outage, they stop and will be off by the length of the outage. To avoid problems with power outages, the new wall switch has backup power, but I’m not sure whether that is a rechargeable battery or a supercapacitor that will hold a charge for a while without power; some other brands use disposable CR2 batteries. The supercapacitor would be best because it would never wear out. I kind of wonder how much energy the timers use. Part of the point is to save energy by turning off the light when it isn’t needed, but compact fluorescents don’t use that much energy anyway. I read somewhere that they may use 4 watts, while the bulb itself is maybe 12 watts. So while the bulb is on, you’re up to 16 watts.



For my back porch, if I were to get a switch, I would probably have it come on at sunset and go off at about 1 AM. Then I could have it come back on at about 6:30 AM when I get up and go off again at sunrise. The problem with that is sometimes the sun rises before 6:30 AM, so it might not get to an off condition until the next day. You can do multiple on-off pairings, so I might be able to get around that by having another on-off program that would turn the light off at 8:30 AM regardless. Well, I checked Star Walk and the earliest the sun rises for the entire year is about 6:25 AM, so I could just have the light come on at 6:20 and then go off at sunrise and I should always be okay, depending on how accurate its sunrise calculation is. If there is a neutral wire in the box for the back porch light, I will definitely get one of these for that switch too.

Date Sunrise Timer Error Sunset Timer Error
7/29/13 6:49 6:49 n/a 8:40 8:40 n/a
8/26/13 7:09 7:04 5 min (25%) 8:11 8:18 7 min (24%)
9/22/13 7:27 7:19 8 min (21%) 7:34 7:56 22 min (33%)
10/26/13 7:53 7:37 16 min (25%) 6:51 7:29 38 min (35%)
11/23/13 7:19 6:53 26 min (29%) 5:31 6:07 36 min (28%)
12/26/13 7:42 7:11 31 min (27%) 5:35 6:11 36 min (29%)
1/26/14 7:39 7:08 31 min (28%) 6:03 6:29 27 min (23%)
2/27/14 7:10 6:48 22 min (27%) 6:32 6:44 12 min (18%)
3/31/14 7:28 7:19 9 min (23%) 7:57 8:07 10 min (23%)
4/27/14 6:54 6:59 4 min (80%) 8:18 8:23 5 min (29%)
5/26/14 6:32 6:36 4 min (24%) 8:39 8:40 1 min (100%)
6/26/14 6:30 6:31 1 min (5%) 8:52 8:59 7 min (37%)
8/3/14 6:53 6:51 2 min (50%) 8:36 8:36 0 min (37%)

21 thoughts on “Solar Timer

  1. It has been about 10 days and, according to Star Walk, the current sunrise and sunset are 6:55 and 8:30 today, changing by 5 minutes and 10 minutes respectively. The timer is already off a little bit, saying the times are 6:54 and 8:32.

    I got another switch for the back porch and will probably install it this weekend.

  2. I installed a second switch for the back porch light. The latest the sun rises is 7:50, so I could set up one timer in the morning to turn the light on at 6:45 when I get up and then go off at sunrise. But for days when sunrise is earlier than 6:45, I would need a program to turn the light on at 6:45 and go off at 7:50, otherwise the light would stay on all day. That wastes an hour of light, but only for 81 days, whereas having the light come on before the sun ever rises (6:25) would waste 20 minutes every day of the year. I can also set it to do this only during the week, figuring that on weekends I will probably sleep through sunrise no matter what time it is.

  3. It has been 4 weeks since I set up the first timer. Today the timer said sunrise was at 7:04 and sunset at 8:18. Star Walk says the correct times are 7:09 and 8:11. This difference of 5 and 7 minutes is concerning because last night it was pretty dark before the light came on. The original times I entered were 6:49 and 8:40, so the sun has lost 20 and 29 minutes. The timer is off by 5 minutes out of 20 minutes (25% error) and 7 minutes out of 29 minutes (24% error). The earliest the sun will ever set is 6:28 (daylight time; it will be 5:28 standard time at that point), so there is another 43 minutes of change. At 25% error, that will add another 10 minutes of error, meaning it will be pretty dark before the light comes if the error rate is consistent (the light would come on 17 minutes after sunset).

    Also the clock itself was behind by 3 minutes. It could be I just didn’t enter the correct time when I set it up, so I will keep an eye on that after correcting the clock today.

  4. Today is the first day of Fall, which maybe means something regarding the sunrise and sunset times. The clock on the timer is 2-3 minutes behind right now (I didn’t reset it, but it could be that while I am checking the settings, I am pausing time) and it says the sunrise is 7:19 with the sunset at 7:56. It was pretty much dark when the light came on today though. StarWalk says the sunrise and sunset today were 7:27 and 7:34. So on sunrise, the sun has lost 38 minutes from when I originally installed the switch and the switch is off by 8 minutes, or 21% error. On sunset, the sun has lost 66 minutes and the switch is now off by 22 minutes or 33% error! No wonder it was so dark. This is really pretty bad. I could have set the timer to come on 22 minutes before sunset and it would be nailing it right now, but the days will still need to get substantially shorter. So right now I’m thinking these timers are pretty lousy and would not recommend them. There are other timers that use coordinates and could potentially be much more accurate. One other solution would be entering MID for the region instead of SOUTH, but that could potentially overcorrect the sunrise and sunset times.

  5. I bought a defiant daylight adjusting digital timer. It is the kind you plug in to an outlet and I think yours is the wire in kind, but I could be wrong. I am setting mine up and did set up DST as on and the sunrise and sunset for today. I’ll watch and see how it keeps time. I THINK we can set these up to come on at a set time and not rely on SR and SS which might be easier, just choosing 4:30 to come on and 8am to go off. It would be nice for it to follow SR and SS, I agree. If not,….

    I am wondering if there is a way to tell this timer (457864) to come on at SR and SS on the weekdays and to stay on all the time on Sat and Sun? is this type of set up possible? I’ve read my instructions but do not see anything that speaks to this clearly. It does tell us what to do to set it up to come on/off M thru F but it does not indicate what the status is on sat sun? Is it left of or left off? Does this make sense? I’m hoping for some helpful feedback. I hope it is ok to ask here.

  6. Mine is wired into a switch and has different sets of days, so it can do every day, any individual day, plus combinations that include weekdays, weekends, Tue/Thu, and Mon/Wed/Fri. If I press SETUP twice to program modes and then hit ENTER for program P4 (or whatever program) I can then cycle through all the day variations, then set an On/Off cycle based on time or sunrise or sunset. So you could have P1 set for Mon-Fri and then P2 set for Sat/Sun. There are 7 different programs available. Looking up the product description for yours, it also has 7 programs available.

  7. Well, with the time change it doesn’t matter so much that the timer is off (now by more than half an hour) because by the time I get home from work, the light is already on.

  8. I checked the numbers today. It is harder to calculate the error with daylight savings time, but I think I got it right. Sunrise is now 11+60+19 = 90 minutes later and the timer is off by 26 minutes, so the error is 29%. The sunset is now 40+60+29 = 129 minutes earlier than when I first started tracking, and the error is now 36 minutes, which is 28% error, so sunset is actually getting a little better than last time, while sunrise continues to get worse. The clock continues to lose time and is now 7 minutes slow.

  9. The clock is off by 10 minutes now, and the error on sunrise is 30 minutes at both sunrise and sunset, but percentage wise the error isn’t getting any worse. The error should go down as the days start to lengthen again.

  10. The clock is 11 minutes slow now. A quartz clock will gain or lose about 15 seconds per month, and this clock loses 1 or 2 minutes per month. But the days are getting longer now and the sun has headed back towards when the timer thinks the sun sets, reducing the error by 9 minutes. I suspect the sun will catch up and then pass the timer, leaving the timer coming on too early in the summer. Not as much change in the sunrise time for right now. Whereas the sunset time reached its earliest in early December, the sunset reaches its earliest about a month later.

  11. Perhaps I over reacted. I was starting to see hints of madness in this thread. But there is a fine line between madness and genius….

    We have two security flood lights that I like. They are set to turn on in a dim mode as it gets dark then stay that way for 5 hours. But they also go into bright mode for 5 minutes if they say see any movement. They’ll do that at any time at night. There are switches to set 3 variables:
    1. Range of motion sensor
    2. Time of dim mode in hours starting at dusk: (1 / 3 / 5 / all night)
    3. Time of bright mode in minutes at any time at night: (1 / 5 / 10 / 15)

    Much simpler and always on time because it is all triggered by the sun (or lack there of.)

    • Probably neither madness or genius. I am just trying to track how well the timer tracks the sunrise and sunset time over the course of a year, by adding a data point each month. That table is at the bottom of the main article and I am adding to it. I will STOP! after a year.

  12. With only two months to go, the timer has cycled back pretty close to the correct sunrise and sunset times, but the clock itself is off by 20 minutes now.

  13. I tracked the timer for a year. During that year the clock lost 21 minutes and the sunset and sunrise times were off by as much as 38 minutes. So not that impressive. I think for this year I will reset the latitude to MID which may overcorrect.

  14. My Defiant Timer lost time too. I reluctantly tried to reset it to correct the time, but I got stuck in a loop where the time is constantly flashing but changing, and the reset button doesn’t get me out of the loop. I’ve called the Help Line and await a call back. Any suggestions in the meantime for initializing this device?

    • I haven’t had that problem. If you disconnect it or turn the breaker off for a little while, that might reset it, but you would at least have to re-enter the time.

    • I sent Judith an email and she said she was able to fix it herself by playing around with the reset button to get it unstuck, which involved pressing it quickly and/or lightly.

  15. Hi, I bought the timer you are discussing. The dawn and dusk presets are quite a bit off, like an hour or more in my location, northern Ohio. When I set it up in the dawn/dusk mode and adjust the times it will not work. You mentioned that the times can be adjusted up to about 15 minutes, do you know the max? If in the Timer mode, do you know if the device adjusts astronomically with those times? Thanks for your help, Tom

    • On mine, in the setup for the time and date, I also enter the time of sunrise and sunset. So at least I am able to start off pretty close. Even though I am in the south, I set my region to MID which seems to track better. Still the timer loses time and needs to be adjusted a couple of times per year.

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