average light intensity from sine equation

Pressure fluctuations caused by sound waves are much easier to measure. There are some optical techniques that make it possible to image the intense compressions are rarefactions associated with shock waves in air, but these are not the kinds of sounds we deal with in our everyday lives. The period of a sound wave is typically measured in milliseconds. For typical sound waves, the maximum displacement of the molecules in the air is only a hundred or a thousand times larger than the molecules themselves - and what technologies are there for tracking individual molecules anyway? The velocity and acceleration changes caused by a sound wave are equally hard to measure in the particles that make up the medium.ĭensity fluctuations are minuscule and short lived. Measuring displacement might as well be impossible. The density amplitude is the maximum change in density.The pressure amplitude is the maximum change in pressure (the maximum gauge pressure).Amplitudes associated with changes in bulk properties of arbitrarily small regions of the medium.The acceleration amplitude is the maximum change in acceleration.The velocity amplitude is the maximum change in velocity.The displacement amplitude is the maximum change in position.Amplitudes associated with changes in kinematic quantities of the particles that make up the medium.High-definition televisions range from 450 to about 1500 cd/m 2.The amplitude of a sound wave can be quantified in several ways, all of which are a measure of the maximum change in a quantity that occurs when the wave is propagating through some region of a medium. Most consumer desktop liquid crystal displays have luminances of 200 to 300 cd/m 2. Typically, calibrated monitors should have a brightness of 120 cd/m 2. From Wikipedia 'The sRGB spec for monitors targets 80 cd/m 2. It is used to characterize the amount of visible light from a light-emitting surface, such as the light provided by a display device. The candela per square meter (cd/m 2) is the derived SI unit of luminance for a surface. It is approximately equal to the old unit 'candlepower' and is generally taken to be equivalent.įor an isotropic source, the relationship between the candela and lumens is 1 cd = 4π lm and the unit relationships is 1 cd = lm/sr. The candela is then used to define the lumen and other quantities used in the measurement of visible light. The candela is abbreviated cd and its standard symbol is I v. of a source that emits monochromatic radiation of frequency 540 x 10 12 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian. The candela is the luminous intensity, in a given direction. It is one of the seven foundation SI units. The candela is the foundation unit for the measurement of visible light. An interesting aspect of lambertian reflection is that although the luminous intensity will be half as much at that angle, the visual area that your eye sees is also half as much, so the surface appears equally 'bright' from that angle. The ray showing 50% is at the angle 30° from the surface where cos 60° = 0.5. For an ideal lambertian surface the reflection will follow the cosine law. Reflection from a surface can be complicated by surface roughness. The intensity or pointance from such a surface in any direction is proportional to the cosine of the reflected angle. For example, an evenly illuminated flat surface such as a sheet of paper is approximately lambertian in that the luminance that you see from any direction is essentially the same. It behaves according to the inverse square law.Ī flat surface that reflects or emits equal luminance in every direction from the surface is said to be a lambertian surface.

Unit illustrationįor a point source, the emitted light intensity or pointance is the same in all directions, or isotropic. In the luminous case it is measured in lumens/m 2 steradian which is equivalent to candela/m 2 = nit. In the radiant case it is measured in watts/m 2 steradian and is also called radiance. The power per unit area per unit solid angle is sometimes called sterance. Otherwise, for a flat radiating surface, known as a lambertian, the intensity falls off as the cosine of the observation angle with respect to the surface normal. If the intensity ( I = dΦ/dω ) of a source is the same in all directions, the source is called isotropic.

For visible light it is expressed in lumens per steradian = candela. In the case of radiant power, it is expressed in watts per steradian. It expresses the directionality of the radiated energy and is appropriate for the description of point sources. The power (flux) per unit solid angle (sometimes called pointance) is the nearest precise terminology to the common term intensity.

Average light intensity from sine equation