Dusk/Dawn sensor question

[beyond the blue]

I have just fit some outside lights with a separate Dusk/Dawn sensor and everything works fine. When I ordered the sensor there was different fixed lux levels available ie. on at 20 lux off at 80 lux, on at 20 lux off at 120 lux etc. My question is, why would manufacturers decide that if 20 lux was a good level to switch lights on, why then set a higher level for them to switch off. Why not nearer the same level.

 

[TopBanana]

It can help stop on/off cycling, so if you switch all the lights on at 20lux you may find the ambient light level near the sensor increases to over 20 - you don't want them getting stuck in that cycle.

 

[beyond the blue]

Yep, that makes sense, cheers.