Count specific range of output as 1 single output

There are two distinct problems here.

The first problem is to convert the analog reading into a binary value. You measure a value between 314 and 856, and you want to know whether the LED is ON or OFF. The simplest solution is to compare the reading to a threshold that is roughly in the middle of the range you measure. You could say, for example, that the LED of OFF if the reading is below 580, and is ON otherwise:

bool led_is_on = analogRead(ldr_pin) >= 580;

If the readings are noisy while they cross the threshold (does not seem to be the case in the short span of data you show), you may want to use some noise cancelling techniques. You could, as suggested by Michel Keijzers, require multiple consecutive “ON” reading before deciding the LED is actually ON. Or you may research the technique of using hysteresis, which would be my favorite solution, as it is extremely simple. However, if your readings are always as clean as what you are showing us (never fluctuating mid-range), you can stick with the simple threshold solution shown above.

The second problem is called edge detection. You want to count the blinks. For this, you need to count how many times the LED turns ON, which is not the same as how many times the LED is ON. You know that the LED turned ON if you just detected it is ON and, on the previous iteration it was OFF. So you have to remember whether the LED was ON last time you looked at it. This means you have to store this information (whether the LED was ON) in a static (or, if you prefer, global) variable. Which leads to the following program:

int blink_count;

void loop() {
    static bool led_was_on = false;
    bool led_is_on = analogRead(ldr_pin) >= 580;
    if (!led_was_on && led_is_on) {
        blink_count++;
    }
    led_was_on = led_is_on;
}

Note the condition: !led_was_on && led_is_on means “The LED was not ON and now it is ON”.

I'm not sure what the value 400 is used for exactly, but the code below is for increasing the counter when at least 6 consecutive values above 800 are occurred.

The key is to use a state machine. I don't have a compiler at hand so forgive possible syntax errors. First we define a state. In your case, there are only two possibilities, so a boolean (bool) is used, normally an enum is used.

bool _counting = FALSE; 

We also need a constant (or define) and a counter to see how many ON values are needed before incrementing the counter, which counts downwards to 0 (and can go negative when more ON values occur).

const int MIN_FLASH_LENGTH = 6;
int _onBeforeIncrementing = MIN_FLASH_LENGTH;

However, we can use the last variable to see if counting is occurring, so we do not have to use the boolean above.

Then we need a counter for the amount of flashes itself:

int _amountOfFlashes = 0;

Both of these are global variables.

Furthermore, in the loop, we need to check for the LED value.

Thus the entire code will be:

const int MIN_FLASH_LENGTH = 6;

int _onBeforeIncrementing = MIN_FLASH_LENGTH;
int _amountOfFlashes = 0;

void loop()
{
    int ledValue = getLedValue(); // Use your code here
    if (ledValue >= 800)
    {
        _onBeforeIncrementing --;
        if (_onBeforeIncrementing == 0)  // Flash of enough length occurred
        {
            _amountOfFlashes++;
        }
    }
    else // Restart counting
    {
        _onBeforeIncrementing = MIN_FLASH_LENGTH;
    }
}

The code fragment

if (_onBeforeIncrementing == 0)
{
    _amountOfFlashes++;
}

can be reduced to:

 _amountOfFlashes += (_onBeforeIncrementing == 0) : 1 : 0;

Also note if you have more code to add, to use the name LED or LDR into the global variables for clearity.

By my understanding you want to count the values where your LED is on (800+ values in your case).

For this you can simply create an if condition where in you say if the value is greater than 800 increase counter by 1

int count = 0;

if(value>=800):
    count++

Here the variable value is the data you are printing on your serial monitor and count is your counter.

Also add the if condition inside the loop function and the declare the variable count = 0 outside the loop function