light-time.pde

#include <Wire.h>
#include "RTClib.h"
#include <SPI.h>

#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

// If using software SPI (the default case):
#define OLED_MOSI   9
#define OLED_CLK   10
#define OLED_DC    11
#define OLED_CS    12
#define OLED_RESET 13
Adafruit_SSD1306 display(OLED_MOSI, OLED_CLK, OLED_DC, OLED_RESET, OLED_CS);

#if (SSD1306_LCDHEIGHT != 32)
#error("Height incorrect, please fix Adafruit_SSD1306.h!");
#endif

int lightPin = 0;  //define a pin for Photo resistor
int buttonPin = 7;
boolean lightOn = false;

RTC_DS1307 RTC;


void setup()   {                
  Serial.begin(9600);
  
  // enable internal pull-up
  pinMode(buttonPin, INPUT);
  digitalWrite(buttonPin, HIGH);

  // by default, we'll generate the high voltage from the 3.3v line internally! (neat!)
  display.begin(SSD1306_SWITCHCAPVCC);
  // init done
  
  display.clearDisplay();
  display.setTextSize(2);
  display.setTextColor(WHITE);
  display.setCursor(0,0);

  display.println("Ready.");
  display.display();
  
  delay(1000);
  display.clearDisplay();
  display.display();
  
  Wire.begin();
  RTC.begin();
 
  if (! RTC.isrunning()) {
    Serial.println("RTC is NOT running!");
    // following line sets the RTC to the date & time this sketch was compiled
    RTC.adjust(DateTime(__DATE__, __TIME__));
  }

}

void reset() {
  lightOn = false;
  
  display.println("Resetting...");
  display.display();
  delay(1000);
  display.clearDisplay();
  display.setCursor(0,0);
  display.println("Done");
  display.display();
  delay(1000);
  display.clearDisplay();
  display.display();
}

void timenow() {
    DateTime now = RTC.now();
 
    display.clearDisplay();
    display.setCursor(0,0);
    display.print(now.hour(), DEC);
    display.print(':');
    display.print(now.minute(), DEC);
    display.print(':');
    display.print(now.second(), DEC);
    display.println();
    display.display();
}

void loop() {
  
  // light level 850 for light is on, less than that, is ambient light
  int value = analogRead(lightPin);
  
  int resetFlag = digitalRead(buttonPin);  // read input value

  if (resetFlag == LOW) {         // check if the input is HIGH (button released)
    reset();
  }

  if (lightOn == false && value > 850) {
    lightOn = true;
    timenow();
  } else if (lightOn && value < 700) {
    reset();
  }
  
  delay(10); //short delay for faster response to light.  
 
}

This is awesome. I instantly feel like porting it to Johnny Five :D