Okay, let's break down the pros and cons of each option and then discuss the best approach

1. Digital Time Clock (nDTC) ONLY:
Pros



Precise Scheduling

You can set very specific on/off times, days of the week, holidays, etc. You have a lot of control.

Predictable Operation

The lights will turn on and off exactly when programmed, regardless of weather conditions.

Override Capabilities

Most digital time clocks have manual override buttons, allowing you to turn lights on or off as needed, bypassing the programmed schedule.

Energy Savings (potentially)

By setting precise schedules, you avoid lights being on longer than needed, particularly during shorter nights or periods of adequate ambient light.

Cons



Lack of Flexibility

They don't automatically adjust for seasonal changes in sunrise and sunset times. You'll need to adjust the on/off times several times a year.

Inaccurate Activation on Cloudy Days

On overcast days, the lights might not be needed at the scheduled "on" time, leading to wasted energy.

Potential for Manual Intervention

Someone has to remember to change the schedule regularly. If not, the lights will either come on too early or too late.

Reliance on Programmed Accuracy

If the clock loses power or the programming is corrupted, your lighting schedule could be disrupted.

2. Photocell (Light Sensor) ONLY



Pros



Automatic Adjustment

The lights turn on and off based on actual light levels. This automatically adjusts for seasonal changes, cloudy days, and varying levels of ambient light.

Energy Efficiency

Lights only come on when it's actually dark enough to warrant them.

Hands-Off Operation

No manual adjustments are necessary.

Cons



Limited Control

You can't set specific on/off times. The lights will come on when it gets dark enough and turn off when it gets light enough.

Sensitivity Issues

Photocells can be fooled by nearby artificial light sources (e.g., streetlights, car headlights) or shadows, causing them to switch on and off erratically or at the wrong times. Placement is crucial.

Lack of "On-Demand" Control

You can't easily override the photocell to turn the lights on early for security or specific events.

Potential for premature failure. Exposure to the elements can cause degradation over time.3. Combination of Digital Time Clock and Photocell (BEST OPTION)



How it Works

The photocell is wired in series with the time clock. The time clock controls when the circuit is potentially powered. The photocell only allows the circuit to complete (and thus power the lights) when the light level is below its set point and the time clock is in its "on" period.

Pros



Maximum Control and Efficiency

You get the best of both worlds. The time clock sets general on/off times, while the photocell fine-tunes the operation based on actual light levels.

Seasonal Adjustment

The photocell handles seasonal variations in sunrise and sunset.

Override Capabilities

Most time clocks allow manual override, so you can turn the lights on outside of the programmed schedule if needed.

Flexibility

You can configure the time clock to turn the lights on only during certain hours (e.g., dusk to dawn, or only during specific evening hours).

Energy Savings

The photocell prevents lights from coming on during unusually bright days within the programmed "on" time.

Added Safety Net

If the time clock fails, the photocell can still provide some level of automatic lighting control (although potentially less efficient).

Cons



More Complex Wiring

The wiring is a bit more involved than using just one device.

Higher Initial Cost

You need to purchase both a time clock and a photocell.

Recommendation

The

combination of a digital time clock and a photocell is almost always the best solution for exterior lighting control. It provides the greatest flexibility, energy efficiency, and reliability.Here's a suggested configuration:1. Time Clock

Program the time clock for a general on/off schedule that covers the period of time when you typically want the lights on (e.g., from 30 minutes before sunset to 30 minutes after sunrise). Slightly overestimate the dark hours to give the photocell some leeway.2.

Photocell

Mount the photocell in a location that is exposed to natural daylight but not directly illuminated by artificial light sources. Adjust its sensitivity so that it turns the lights on when it gets dark enough and off when it gets light enough.3.

Wiring

Wire the photocell in series with the time clock's output. This means the time clock provides power to the photocell, and the photocell only allows the power to flow to the lights when it's dark enough.

Troubleshooting Tip: If your lights aren't working as expected, check the following: Is the time clock programmed correctly? Is the photocell functioning? You can test it by temporarily covering it with something opaque (like a piece of cardboard) to simulate darkness. The lights should turn on. Are all the wiring connections secure?* Are there any obstructions blocking the photocell's view of daylight?By combining the strengths of both a digital time clock and a photocell, you can create a highly effective and efficient exterior lighting control system. Flag for review