The Value of Light or Measures of Brightness
To begin with we have a specific brightness of light at any given time. Different times of the day, conditions, cloud cover etc. provides for changing light values. It is just like the temperature, it is never static, but it is totally measurable. At 72 F or 20 C we are comfortable, if we increase the heat to 100 F or 37.8 C we are too hot, and when it is 20 F or -6.7 C we are cold.
We can measure light and we say that the “light level” or “light intensity” is “X”. Light is measured in the European version as “LUX” or the North American format of “foot candles”. A foot candles measurement is the amount of light that one candle can emit at a distance of one foot. Naturally, when you have more candles it will be brighter. Another measurement that we know of when dealing with artificial light, is that light loses its brightness inversely proportional to the square of the distance. In other words, if we have one-foot candle power at one foot, by being another foot farther away the light level is not halved but quartered. We’ll get into this more when we discuss flash photography. For now, you can see various light levels outdoors under different conditions.
Light Level or Illuminance, is the amount of light measured in a plane. The work plane is where the most important tasks in the room or space are performed.
MEASURING UNITS LIGHT LEVEL – ILLUMINANCE
Illuminance is measured in foot candles (FC) or LUX ). A foot-candle is actually one lumen of light density per square foot, one lux is one lumen per square meter. Condition Illumination
• LUX = FC (10.752)
• FC = LUX / 10.752
COMMON LIGHT LEVELS OUTDOOR
1 Stop or unit of Light Overexposed
1 Stop or unit of Light Underexposed
Determining the proper exposure.
Ok, let’s get back to determining proper exposure. As we discussed in our last post, the camera sensors are geared to read the part of the scene you are metering as if it looked like it was 16% gray. If what you are looking at is white, then the picture would turn out darker because the sensor thinks it is light gray. Opposite to this, when you are looking at something that is dark and the camera thinks it is 16% gray, the picture would turn out too light. This is where your creativity and imagination kick in.
If you want as close to the “best” exposure as possible you would look at the scene and imagine it as a black and white scene and then pick an area that looks close to 16% gray and use that area to meter for the best light level reading. You now get to turn this “level” into the exposure that you want to use to create the image you want.
How do we translate the exposure reading into the image we want?
Now we get into the trinity of photography; aperture, shutter speed, and ISO. By properly adjusting these three elements you will get the exposure you. That we will discuss in our next blog.
Night at the Bellagio – always a tough exposure
We hope this will help you get the images that you imagined and deserve.
Good shooting and understanding light!
Bob and Chuck
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