Illuminating a foot diameter wall clock at night?

[hermitjohn]

I have a battery alarm clock with an illumination circuit. Runs on 3AA batteries. Think I gave $8 or $9 few years back on closeout. Apparently no longer sold. Anyway it has a photocell that turns on what must be very tiny LED in dark room. Sort of a green glow. Circuit is set up so when battery voltage drops to certain point, clock continues, the light does not. Usually works about 2 to 3 month. For all I know maybe one AA cell powers the clock and the other two do the LED?? Never curious enough to test it to find out.

Well even at its best, not easiest thing to see small clock face across the room and I dont need an alarm. Have a large wall clock that runs long time on one AA battery. Like to find economical way to illuminate it using battery and LEDs.

I can wire up a 5mm LED connected to a 6V lantern battery and make it last long time albeit at very dim light output. Have to experiment with resistors to get it bright enough to read clock while dim enough for the battery to last at least six month. However I wondered how to make a photo cell circuit to turn it on at dusk and off at dawn since its pointless to have it running 24/7. Only premade photocell switches I found were ones were for 12Vdc or for 120VAC though they were very cheap on ebay. I am guess such a circuit would use a photo resistor, a transistor, and probably some regular resistors. No idea what values nor can I seem to find a website spelling it out.

Most outdoor LED lights use motion sensor to make any batteries last. Did finally find one with photocell. Says on dusk to dawn and its three AA batteries will last up to a year. About $14 shipped. More research and turns out a firefly would put it to shame. Apparently half a lumen. Give you an idea where path is when its pitch black, but probably not enough light for more than that. (follow the fireflies!) Still gotta admire getting any visible light to last a year on three AA batteries! Guessing maybe a 3mm LED with big resistor?? I suppose something like that could be modified to run brighter and use three D cells.... I would be very happy to have an illuminated wall clock I could read across a dark room that only used three D cells a year.

[hermitjohn]

Maybe finding my own answer. Here is an instructible that uses 9V battery: www.instructables.com/id/Blue-Bawls-automatic-LED-light/?ALLSTEPS

And here is one that uses a 3V coin battery: www.evilmadscientist.com/2007/a-simple-and-cheap-dark-detecting-led-circuit/

[hermitjohn]

New and improved version:

www.evilmadscientist.com/2008/a-dark-detecting-circuit-for-your-jack-o-lantern/

[hermitjohn]

That light advertised going whole year on three AA batteries really had me curious. Never seen one that made this kind of claim. I bought one. Got it today. For sure if mounted as suggested, the light through the white diffuser would be useful as a marker only. It doesnt illuminate anything in useful way. And you would need multiple units close together to mark a path. Its mostly overpriced decoration as designed and marketed.

BUT, I had to take back off to put batteries in it, and found this exposed the LED. Without the white diffuser there is enough light to illuminate a very small area. I put bit aluminum foil behind the led and propped it up over the alarm clock. Voila, I could easily see the clock face and it makes a sort of small nightlight. Havent tried it on the big wall clock yet. Might take equivalent of two of these to illuminate the big clock. Though bit reflective tape on hands and number markings might help also.

Now apparently the phototransistor is filtered as the only way I could get the light to turn off was to put it in the window while it was still light outside. Room lights/lamps on had no effect. Perhaps also because its a cloudy day. Course it was designed to function outdoors.

So question still is how long the batteries last. Hard to believe it would produce useful light for whole year on three AA batteries. But suppose even six month would still make it pretty economical. If I were building my own circuit, would make the phototransistor remote so it could be in window, without clock and light having to be in window. Do it that way cause its still nice that say light from tv doesnt turn it off. I read Amazon reviews of some wall clocks that are backlit. People were disappointed that even in dark room, if tv was on, the illumination didnt happen. And most of these clocks, the backlighting didnt last very long. Some killed the batteries withing a few days. Obviously a poor design.

And Amazon reviews of this light I bought pretty much agreed that batteries will last almost a year. Course none of them were using it inside with back removed to illuminate a clock... LOL They used the light outside as a marker light. Inside with the filtered phototransistor, the light is going to be on more than if it was outside.

[shin]

I'm pleased when a normal no-frills wall clock can run a year on batteries. I've been keeping an eye on the one I bought when I bought the house that's still been ticking fine these past 8 months on 2 AA rechargeables. I was going to give up on it if I had to constantly keep changing them more often than that but thankfully it's ticking still with one time charged rechargables.

I use a big number digital for a bedside alarm clock so I can see without glasses -- disappointingly the thing's backup battery function has never worked. However the rattling device you plug into it and put under the pillow can wake even me up most of the time.

[hermitjohn]

I prefer the alarm clocks that run on one D cell or one C cell. But everything has went to one or more AA and AAA cells. And I much prefer battery clocks over plugin type. My electric goes off at times all year round, so dial clocks are off and the digital clocks sit there flashing at me. Anyway I have had very good luck with clocks going a year or more on whatever batteries they use. What doesnt last is the battery powered illumination. That seems poorly designed in all the battery clocks I have tried. Thus my experiments with this "deck light".

It did well last night. I think it would do even better if small slivers of reflective tape were applied to the hands of clock so they show up better. Again this is very marginal amount of light, but reviews say batteries do last around a year. If that ends up being true then the designer deserves a gold star on his/her forehead. Though the manufacturer is already amply rewarded moneywise for a product that most likely costs less than dollar for them to make and retails for $14.

[hermitjohn]

Improved it even more, bent the legs of the LED 90 degrees and positioned the light further out in front of the clock face. Lot better lighting, though I now have a weird shadow from the second hand depending angle I look at it. I think I get that reflective tape and put couple bits of it on end of both hour and minute hands and that should take care of things. Way it is now, at times the black hands and the black shadows get confused.

I also ordered some super cheap bits and pieces off ebay via slow boat from China to make my own phototransistor LED circuits. For what I gave for the one factory glow light, could probably make a hundred homemade ones with ebay parts. Meaning I guess if I ever wanted bunch outdoor marker lights, could just make the circuits and stick them inside old pop/water bottles from recycling center to weather proof them.

[hermitjohn]

Thinking about it, if these truly last a year on three AA batteries, heck you could put a bunch of these (affordable homemade version) in an off grid cabin and at least have enough light to navigate at night without flashlight. Get it aimed right and you could read with one. Yea, could brag that you power your house on AA batteries.... LOL Though I am sure a small solar panel system would be more practical, not as cheap, but more practical long term.

[shin]

Power your house on AA batteries, LOL! That's pretty good hermitjohn!

[hermitjohn]

That overpriced marker light that I bought to see if its claim of one year on set batteries was true. Well getting close and its not dimming. Looks like it will make it. The reflective tape on clock hands really didnt do much. But removing that diffuser and bending led legs so it shown down onto clock face helped a lot.

I have the parts, never did get homemade version put together. But when I realized nearly year had passed and clock still illuminated, gives inspiration to hunt up pieces and put together a homemade one. Should last just as well and whole lot cheaper.

I am truly amazed batteries lasted a year (well nearly a year, but no signs of failing anytime soon). Rare one expects truth in advertising. They tend to count on people not really paying attention to passage of time and just tossing it when it quits without much consideration. I mean its a trivial thing, not like your new $40k pickup giving you problems where big bucks involved force you to pay close attention.