[Caesar Soze]

No, genius. You conserve the batteries to save you the expense and trouble of having to go out and replace them in two weeks. The cost of the batteries is negligible, as is the cost of a photo cell. The expense is in the labor. These things were designed to be placed and left, presumably. A unit that only works in the dark will work for twice as long.

So you think the people that put these up were considering visiting them regularly to maintain them? They were intended to be left, then found later and kept as souvenirs. The CEO of the marketing company said as much to the Boston Globe. I doubt anyone thought they'd be up more than a couple days. The photosensor would've added costs in material, brainpower, and labor for something that is basically a throwaway advertisement -- a high-tech flier.

[bondjamesbond]

They were intended to be left, then found later and kept as souvenirs. The CEO of the marketing company said as much to the Boston Globe. I doubt anyone thought they'd be up more than a couple days. The photosensor would've added costs in material, brainpower, and labor for something that is basically a throwaway advertisement -- a high-tech flier.

If you could have your high tech flier work for four days instead of two for the cost of the addition of a 35 cent photocell, wouldn't you add the photocell?

I'm just speculating, of course. I have no idea if there was a photocell included, here. My electronic knowledge is derived largely from the old 100-in-1 kit I had as a kid. But a photocell switch is pretty easy to make.