曝光计是一种用来量度热辐射功率的仪器。一般用于气象学，用来量度源自太阳的辐射，又或充当太阳热力计来使用。

一般来说，曝光计会利用物理或化学的方法来量度辐射量，但方法都是计算在每单位时间内，仪器所能够收集的光子数量。这个仪器可以用来量度紫外光及可见光，视乎测量物料而定。例如：草酸铁溶液（例如：草酸铁钾）就可以用于化学式的曝光计。至于物理式的，一般用采用辐射热测量计、电热堆（thermopile）及光电二极管，并透过对读数与光子数量的调较，从而计算出热辐射功率。

一般的典型曝光计不需要操纵，可自动进行监测。量度单位是「瓦特每平方米」（W/m）。

Actinometers are instruments used to measure the heating power of radiation. They are used in meteorology to measure solar radiation as pyrheliometers.

An actinometer is a chemical system or physical device which determines the number of photons in a beam integrally or per unit time. This name is commonly applied to devices used in the ultraviolet and visible wavelength ranges. For example, solutions of iron(III) oxalate can be used as a chemical actinometer, while bolometers, thermopiles, and photodiodes are physical devices giving a reading that can be correlated to the number of photons detected.