# How much light is 1 stop?

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#### sweat100

##### Senior Member
Wonderd the above question. What units it holds? (cadela, lux, lumens, time etc???) i have read that decrease of shutter of 1/125 to 1/60 is considerered 1 stop increase. How about decreasing form 15s to 30s? Is it considered 1 stop too?

#### ckiang

##### Senior Member
Originally posted by sweat100
Wonderd the above question. What units it holds? (cadela, lux, lumens, time etc???) i have read that decrease of shutter of 1/125 to 1/60 is considerered 1 stop increase. How about decreasing form 15s to 30s? Is it considered 1 stop too?
Yup, both are 1 stop difference.

There is no concrete/absolute amount of light in "n stops", coz that's only a measure of the difference between 2 settings. The amount of light is measured by exposure, which is a combination of ISO, shutter speed and aperture. There's a formula which takes these 3 and give you the Exposure Value (EV), which is then the absolute value.

EV = log2(aperture² x (1/shutter speed) x (ISO sensitivity/100))

Regards
CK

#### denizenx

##### Senior Member
1 stop is like power of 2...
light is measured in EV for cameras and lux for light.
It is the amount of illumination provided when one Lumen is evenly distributed over an area of 1 square Meter. This is also equivalent to the illumination that would exist on a surface all points of which are one Meter from a point source of one Candela. Lux = lm/m^2 = m^(-2)*cd
cd is Candela, light given by one std candle... LOL

not terribly useful trying to relate it to real world unless u got a lightmetre...

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