Exposure Value
Exposure value (EV) is a measure of the amount of light used in a photograph. The brighter the light, the higher the number of the exposure value (EV). An exposure value of 0 means there was no light at all.
Exposure value, or EV, is a measure of light intensity. It’s based on the amount of light required to produce an exposure of a certain duration.
For example, if you’re shooting with a camera that has an ISO setting of 100 (and the shutter speed and aperture are fixed), at f/8 and 1/125 second, your exposure value will be 1/125 second at f/8 ISO 100. If you change your shutter speed to 1/500 second, but keep everything else the same, your exposure value will increase to 1/500 second at f/8 ISO 100.
EV can also be used as a way to calculate exposure settings when you’re taking pictures manually. For example, if you want a photo to be exposed for 1 second at f/8 ISO 100 (with no flash), then you’d set your camera’s shutter speed to 1 second, its aperture to f/8 and its ISO rating to 100 (or 400 or 800).
The higher the EV number, the greater the amount of light is hitting your sensor. A lower EV number means less light is hitting your sensor.
You can use EV to adjust how bright or dark an image appears on your camera’s LCD screen. This is called exposure compensation, and it’s one way to control how much light reaches your camera’s sensor when shooting in auto mode — either automatically or manually — without having to change any other settings.
In photography, there are two types of exposure: over-exposure and under-exposure. Exposure compensation is used to bring the brightness back up when it’s too dark (over-exposed). You can read more here.
It is measured in two ways: as an absolute value and as a relative value.
Absolute Values
Absolute values are fixed numbers that tell you exactly how much light will enter the camera. The scale ranges from 0 to 20, which means that if you have an EV of zero, nothing will enter the camera, while an EV of 20 means that all of the available light will fall on your sensor without fail.
Relative Values
Relative values are numbers that tell you how much light your photo should contain compared to another photograph taken at a different time of day or under different conditions (for example, one taken indoors versus outdoors). The scale ranges from -2 (1/4 stop darker than normal) to +2 (+1 stop brighter than normal), meaning that if you have an EV of +1, then there will be one stop more light in your image than usual.
The EV scale helps photographers figure out how much light they need to capture an image correctly. If you have too much light in an image, it will appear overexposed and washed out — if you have too little light, your photos will appear too dark and blurry.