Got this on eBay. My first Dark To Light photocell. It has the 2.6 footcandle turn-on level, which I like because the lights come on earlier. Made in May 2008.
8 foot candles?! Those must come on long before dusk. There are some lights here that come on really early and don't even shut off if it's overcast outside. They're white colored and are either Fisher Peirce or Ripley...
Yep! They are for aircraft warning lights which need to be on very early and go off very late, or stay on all day if it's dull. From what I understand the go from 1 FC to 35 FC, you can see this spec sheet showing the levels.
How do you tell what footcandles do PC activate at? Anyways the electronic ones have a adjustment knob inside which I guess adjusts which FC do they turn on at.
@Joe - It says in the specifications and part number. For example, in "DP124-2.6-TJ", 2.6 indicates the turn-on level in footcandles. DTL photocells most commonly use 1.5 ftc turn-ons.