# lighting ratio

#### Howard Cha

##### Senior Member
Lighting ratio in photography refers to the comparison of key light (the main source of light from which shadows fall) to the fill light (the light that fills in the shadow areas). The higher the lighting ratio, the higher the contrast of the image; the lower the ratio, the lower the contrast. Since the lighting ratio is the ratio of the light levels on the brightest lit to the least lit parts of the subject, and the brightest lit are lit by both key (K) and fill (F), therefore the lighting ratio is properly (K+F):F although for contrast ratios of 4:1 or more, then K:F is sufficiently accurate.

I'm studying lighting ration.
I can't figure out the part colored.

Many thanks,
Howard Cha

• #### JulianStuart

##### Senior Member
IF F is small, the difference between (K+F):F and K:F is sufficiently small that you can calculate K:F and use that simpler value (instead of calculating (K+F):F)

#### Howard Cha

##### Senior Member
IF F is small, the difference between (K+F):F and K:F is sufficiently small that you can calculate K:F and use that simpler value (instead of calculating (K+F):F)
Thank you very much!

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