Photo eye hysteresis
I've always found it challenging to commingle industrial controls and discrete components, so I would suggest that you stay away from an RC filter even though it could be made to work.  Even ignoring regulatory issues, the simple packaging differences are a headache at best.

You didn't post specs to your photo sensor, but if your goal is simply to avoid flashing plant lighting around dawn, consider using a time delay relay (off-delay) between the sensor and your contactors to allow a "ride-through" period (really a resettable one-shot) -- ensuring that your plant lights stay on for a minimum period of time regardless of what the sensor's output is. 

Off-delay relays are slightly different than a typical relay, as they require an uninterrupted pilot voltage in addition to the "coil terminals" -- the relay's input.



In this diagram, Input Voltage represents the pilot voltage - essentially the power supply to the time-delay relay, Initiate Switch would be the relay's signal input - coming from your photo sensor, and Load would be the plant lighting via the lighting contactors you already have.  Note how the load stays on after the Initiate Switch has gone low again.  

In your application, the input will be high all night, so the output will remain on all night.  At dawn, when the sensor output tends to flap a bit, you'll ride through those transients as long as they are shorter than the off delay period.  The one downside of this approach is that the lights will stay on a little longer into the early morning than they otherwise might.

Such time delay relays can be purchased from McMaster-Carr or Grainger, and can also be very effectively coded in even the cheapest PLCs.  You'll still need the lighting contactors to carry the lighting load; time delay relays are typically used as pilot relays only.