At a Wal-Mart (on Bowles and 470) They have tons of skylights. and when it gets bright enough, they have some weird photocontrol, and when it gets bright enough in the store all the lights (except the border lights) turn off. but if it is darker, but still bright, the lights are just dimmed. They dim at different rates. but i think most of them are fixed. But they do this to conserve power and lower the electric bill. Never seen the photocontrol, but i wonder where it is...

I've noticed a lot of large stores using skylights for natural light lately.  Walmart is the most extreme example though.  The one in Leesville, La has all its indoor lights dimmed or turned off during the day.

There are "tons" of photocells pointing downwards as well and they are connected in a regulation loop maintaining "constant" illumination level in the area below - if it's darker, it increase the fluorescent power and vice versa. In some systems motorized shade-flaps on these skylight units are attached to the system as well, to avoid uncomfortable overillumination by e.g. noon sun and/or limit the passage of asociated heat - usually when skylights are used in really high quantity. I do like these systems, as nothing might beat the natural sun light quality, but in my area (~50deg North) these are powerfull enough only in summer.

This is referred to as "daylight harvesting" and we are doing it more and more lately.  As dimming ballasts and simple photocontrols come down in cost, you will see lots more of it.  Small photocells are available that physically clip to the lamps and point downward to measure the light.  The simple one we sometimes use can control up to 10 dimming ballasts on the 0-10v control wires.  Other more complex systems can control entire zones.  It's pretty cool, and if done properly, is not noticible to those who inhabit the space.

and if done properly, is not noticible to those who inhabit the space.

Except for us weirdos that spend a lot of time looking UP instead of around!

Quote from: swpidgeon on June 07, 2009, 08:39:04 PM

and if done properly, is not noticible to those who inhabit the space.

Except for us weirdos that spend a lot of time looking UP instead of around!

I agree! 

At my local Wal-Mart (a pretty small one), there's no skylight at all, but some lights are still shut off to save energy. The difference isn't really that big...

Lol, there are still walmarts here in colorado that are small. like the one on wadsworth by costco. they remodeled it, but still, no skylights. cieling tiles. and its small. the one imtalking about that has the powersaving is the new supercenter onbowles and 470. it is new. there used to be nothing where the walmart is. just grtass.and now theres a huge walmart. and they are remodling it for somne reason.

At my local Walmart they have shut off some of the lights during the summer too. I think they shut off 1 2 lamp fixture for every 4 that are turned on. I'll have to check if they have skylights on the ceiling.

This shutting down happen, when lamps would be otherwise set to too low setting, so operate inefficiently.

At my local Walmart they have shut off some of the lights during the summer too. I think they shut off 1 2 lamp fixture for every 4 that are turned on. I'll have to check if they have skylights on the ceiling.

With Walmarts that have these systems, Whats cool is to be there when it gets dark enough for the lights
to turn on (I've seen this multiple times)... <partly cloudy days where the sun goes in&out of clouds
are great for this!>

In the store I usually go to (which weirdly enough is the one mentioned in the 1st post of this thread)
the lights will turn on at full brightness for just an instant (basically just a flash) then be
dim...maybe they need to be full brightness to start? The whole store doesn't turn on as a unit, but
rather in sequence one bank/strip of lights at a time (the end result being they'll all be on dim)

Its very noticeable when the lights are coming on with the flashing...but when they turn off you don't
notice.

When they first built the store it had all cool-white (4100k), then one day they changed everything
out to 5000k color

The full-brightness flash after power ON is caused by the fact, how resonance ballasts control lamp mode:
It start at high frequency, so there is in the resonance circuity not enough voltage to ignite the lamp, but enough current to warm it's electrodes up.
Then it sweep the frequency down towards the resonance to buildup high voltage for ignition.
But when the lamp ignite, the ballast start to regulate the current to the required level. But ignition frequency correspond to quite high power setting (usually about 30..60%), so on the low power setting (5..10%) the ballast has to increase the frequency again. But it should do so without any overshoot, as the lamp might extinguish, so there is usually quite long time constant in changing the frequency, so to sweep it up to reduce the power to required level take time. And during this time the brightness is bigger then the settled state, hence the perceived "flash".

Regarding to the dimming of the lights by the Photo Controls: Many PC based LED nightlights also have such behavior when the light is not bright enough. This behavior of a PC is not suitable for mains voltage lamps like fluorescents and HID lamps.

I was in Walmart friday afternoon and it was one of those days with patches of clouds moving over (the perfect setup ) ... got to see multiple on/off cycles of the lights LOL .. I
<wonder how much 'lamp life' is wasted on those days>


I also noticed there's some cool whites mixed in randomly with the 5000k LOL guess whoever replaces the bulbs got the wrong color

<wonder how much 'lamp life' is wasted on those days>

I would guess not much, as dimming ballasts (nearly without exception - as it mean no extra cost) preheat lamps correctly, so there would never happen any stress from the discharge on too cold electrode.
On some designs (those simpler intended only for such daylight harvesting management - simply working frequency is direct function of illumination level, without any extra feedback) this mean even intrinsic behavior: for lower then minimum setting they only heat electrodes without discharge. So when the control signal changes slowly (what is always the case for moving clouds), it always go across "heat only" section of the operating curve.