I am using the Arduino UNO R3 and Adafruit Data Logger Shield to log temperature, light, and humidity on a FAT32 SD card. The code I have (attached below) is able to create a file, but sensor readings are not added to it. The sensors I am using are the DHT22 Sensor and the BH1750 sensor. I am new at coding and have no idea why this is not working. 
/* This is the initial project code for the IRES Arduino project using both the DHT22 sensor and BH1750 sensor*/
//Libraries
#include "RTClib.h";
#include "SD.h";
#include <DHT.h>
#include <Wire.h>
//Constants
#define LOG_INTERVAL 3000 // mills between entries
#define ECHO_TO_SERIAL 1 // echo data to serial por
#define DHTPIN 2 // what pin we're connected to
#define DHTTYPE DHT22 // DHT22/AM2302
DHT dht(DHTPIN, DHTTYPE); //// Initialize DHT sensor for normal 16mhz Arduino
int chk;
float hum; //Stores humidity value
float temp; //Stores temperature value
int BH1750_address = 0x23; // i2c Addresse
byte buff[2];
//Object and Error
RTC_PCF8523 rtc;
char daysOfTheWeek[7][12] = {"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"};
const int chipSelect = 10; // for the data logging shield, we use digital pin 10 for the SD cs line
File logfile; // the logging file
void error(char *str)
{
Serial.print("error: ");
Serial.println(str);
while(1);
}
void setup(void)
{
Serial.begin(9600);
Serial.println("IRES");
// initialize the SD card
//Serial.print("Initializing SD card...");
// make sure that the default chip select pin is set to output, even if you don't use it:
pinMode(10, OUTPUT);
// see if the card is present and can be initialized:
if (!SD.begin(chipSelect)) {
Serial.print("Card fails, or not present");
// don't do anything more:
return;
}
Serial.println("card initialized.");
// create a new file
char filename[] = "LOGGER00.CSV";
for (uint8_t i = 0; i < 100; i++) {
filename[6] = i/10 + '0';
filename[7] = i%10 + '0';
if (! SD.exists(filename)) {
// only open a new file if it doesn't exist
logfile = SD.open(filename, FILE_WRITE);
break; // leave the loop!
}
}
if (! logfile) {
error("couldnt create file");
}
Serial.print("Logging to: ");
Serial.println(filename);
//For DHT22 and BH1750
dht.begin();
Wire.begin();
BH1750_Init(BH1750_address);
//For RTC
if (!rtc.begin()) {
logfile.println("RTC failed");
#if ECHO_TO_SERIAL
Serial.println("RTC failed");
#endif //ECHO_TO_SERIAL
}
logfile.println("runtime,time,hum,temp,lux");
#if ECHO_TO_SERIAL
Serial.println("runtime,time,hum,temp,lux");
#endif
}
//Additional Coding for BH1750
void BH1750_Init(int address){
Wire.beginTransmission(address);
Wire.write(0x10); // 1 [lux] resolution
Wire.endTransmission();
}
byte BH1750_Read(int address){
byte i=0;
Wire.beginTransmission(address);
Wire.requestFrom(address, 2);
while(Wire.available()){
buff[i] = Wire.read();
i++;
}
Wire.endTransmission();
return i;
}
void loop()
{
DateTime now;
// delay for the amount of time we want between readings
delay((LOG_INTERVAL -1) - (millis() % LOG_INTERVAL));
// runtime, log milliseconds since starting
uint32_t runtime = millis();
logfile.print(runtime);
logfile.print(", ");
#if ECHO_TO_SERIAL
Serial.print(runtime);
Serial.print(", ");
#endif
// now, log actual time using RTC
now = rtc.now();
logfile.print(now.year(), DEC);
logfile.print("/");
logfile.print(now.month(), DEC);
logfile.print("/");
logfile.print(now.day(), DEC);
logfile.print(" ");
logfile.print(daysOfTheWeek[now.dayOfTheWeek()]);
logfile.print(") ");
logfile.print(now.hour()-6, DEC);
logfile.print(":");
logfile.print(now.minute(), DEC);
logfile.print(":");
logfile.print(now.second(), DEC);
#if ECHO_TO_SERIAL
Serial.print(now.year(), DEC);
Serial.print('/');
Serial.print(now.month(), DEC);
Serial.print('/');
Serial.print(now.day(), DEC);
Serial.print(" (");
Serial.print(daysOfTheWeek[now.dayOfTheWeek()]);
Serial.print(") ");
Serial.print(now.hour()-6, DEC);
Serial.print(':');
Serial.print(now.minute(), DEC);
Serial.print(':');
Serial.print(now.second(), DEC);
Serial.println();
#endif //ECHO_TO_SERIAL
//For DHT22
//Read data and store it to variables hum and temp
hum = dht.readHumidity();
temp= dht.readTemperature();
logfile.print(", ");
logfile.print(hum);
logfile.print(", ");
logfile.println(temp);
//Print temp and humidity values to serial monitor
#if ECHO_TO_SERIAL
Serial.print("Humidity: ");
Serial.print(hum);
Serial.print(" %, Temp: ");
Serial.print(temp);
Serial.println(" Celsius");
#endif //ECHO_TO_SERIAL
//For BH1750
delay(2000);
float valf=0;
if(BH1750_Read(BH1750_address)==2){
valf=((buff[0]<<8)|buff[1])/1.2;
logfile.print(", ");
logfile.print((int)valf,DEC);
logfile.print("lux");
#if ECHO_TO_SERIAL
Serial.print("Light: ");
if(valf<0)Serial.print("> 65535");
else Serial.print((int)valf,DEC);
Serial.println(" lux");
#endif
}
//Trying to get this stupid thing to log
logfile = SD.open("filename", FILE_WRITE);
if (logfile) {
logfile.print(runtime);
logfile.print(",");
now = rtc.now();
logfile.print(now.year(), DEC);
logfile.print("/");
logfile.print(now.month(), DEC);
logfile.print("/");
logfile.print(now.day(), DEC);
logfile.print(" ");
logfile.print(daysOfTheWeek[now.dayOfTheWeek()]);
logfile.print(") ");
logfile.print(now.hour()-6, DEC);
logfile.print(":");
logfile.print(now.minute(), DEC);
logfile.print(":");
logfile.print(now.second(), DEC);
logfile.print(",");
logfile.print(hum);
logfile.print(",");
logfile.print(temp);
logfile.print(",");
logfile.print((int)valf,DEC);
logfile.print(",");
logfile.close(); // close the file
}
// if the file didn't open, print an error:
else {
Serial.println("error opening test.txt");
}
}