【Real Time Render 4】

1、Radiometry（辐射量） deals with the measurement of electromagnetic（电磁） radiation（辐射）. Such radiation consists of a flow of photons（光子）. \

　　Photons behave as either particles or waves, depending on circumstance. 

　　光子可以表现为粒子或波。

　　One wave-related property of photons that cannot be disregarded is the fact that each has an associated frequency or wavelength.  The energy of each photon is proportional to its frequency. Different frequencies of photons are perceived as light of different colors.

　　波有频率、波长属性， 能量正比于频率。不同频率的光子对应不同的颜色。

2、The relationships between a photon’s wavelength λ (in meters), frequency ν (in Hertz, or cycles per second) and energy Q (in joules) are：

　　where c is the speed of light (2.998×108 meters/second) and h is Planck’s constant (6.62620 × 10−34 joule-seconds).

3、In radiometry, the basic unit is energy or radiant energy Q, measured in joules (abbreviated “J”).

　　能量单位是焦耳（joule），简写为 J。

　　The radiant flux（辐射流） or radiant power（辐射强度）, Φ or P, of a light source is equalto the number of joules per second emitted (i.e., dQ/dt).  The watt (W) is another term for joules per second.

　　辐射流等于每秒的joules。简称为watt（瓦）。

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