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A key light of 800 footcandles and a fill light of 200 footcandles has a ratio of 5:1 according to the lighting ratio formula — (800 + 200):200 = 1000 / 200 = 5 : 1. The ratio can be determined in relation to F stops since each increase in f-stop is equal to double the amount of light: 2 to the power of the difference in f stops is equal to ...
The melanopic ratio is determined taking into account the source type of light and the melanopic illuminance values for the eye's photopigments. [25] The source of light, the unit used to measure illuminance and the value of illuminance informs the spectral power distribution.
When appearing on light bulb packages, brightness means luminous flux, while in other contexts it means luminance. [5] Luminous flux is the total amount of light coming from a source, such as a lighting device. Luminance, the original meaning of brightness, is the amount of light per solid angle coming from an area, such as the sky.
There are two luminous efficiency functions in common use. For everyday light levels, the photopic luminosity function best approximates the response of the human eye. For low light levels, the response of the human eye changes, and the scotopic curve applies. The photopic curve is the CIE standard curve used in the CIE 1931 color space.
Ordinary people have better reading performance using high-frequency (20–60 kHz) electronic ballasts than magnetic ballasts, [10] although the effect was small except at high contrast ratio. The flicker of fluorescent lamps, even with magnetic ballasts, is so rapid that it is unlikely to present a hazard to individuals with epilepsy . [ 11 ]
While luminance is a linear measurement of light, lightness is a linear prediction of the human perception of that light. This distinction is meaningful because human vision's lightness perception is non-linear relative to light. Doubling the quantity of light does not result in a doubling in perceived lightness, only a modest increase.
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Where SR = suppression Ratio, D = responding during CS and B = responding before CS. If SR = 0, there were no responses during the CS and conditioning is strong. If SR = 1/2, the response rate did not change when the CS was presented and there is no evidence of conditioning; It would be unusual for SR to be greater than 1/2.