Photocell Installation

If you want the light to come on for a fixed period when the sun disappears I'd put it on the west side of the building.

If you are in the extreme North or South there could be an argument for SW or NW respectively.

In practise it probably doesn't make any difference: daylight is very bright compared to night time even on the shaded side of a building.

I generally aim my photocells straight up, so they don't get confused by other street lights, car lights, and such. Have it away from house lights, too.

Put it anyplace. Bye.

better to put it on top for direct sunlight.. sometimes other people add timer for automatic control..

Point the photocell at the north horizon. You want to detect the ambient light level; you don't want the sun directly influencing your trip point. My experience comes from implementing lighting control (indoor as well as outdoor) for Sears (back in the day.) There we used an analog photocell (yes, they make them) so we could control both parking lot lighting at a low ambient level as well as canopy lighting (overhangs at entrances) at a higher level since they get unacceptably dark on just a cloudy day.

As others have pointed out, it doesn't matter too much where you put the sensor, just don't put it where the street light will shine on it.

Speaking of that - Make sure your street light only shines where the light is needed - i.e., down onto the street. Nighttime glare due to poorly aimed (or poorly designed) streetlights can make driving conditions worse.

Also, as a courtesy, be sure the light isn't spilling-over into people's widows or up into the sky.

just don't put it where the street light will shine on it.

Are you sure you've thought that through?

Or is there something about this that I'm completely missing?

In my fair city the streetlights have sensors mounted on the top of the light itself.

You could put it directly under the street light - and the street light will blink On and Off.

(Ok, slightly facetious. Sensor sees a dark sky, turns on the light; light shines on sensor, sensor turns off the light. Rinse and repeat. Not likely to actually happen, but...)