### Instruction:

Extract the cause and effect entities from the following sentence:
For a given spectral value, reflectance is the ratio between the power per unit surface area emitted by a surface and the power per unit surface area (irradiance) incident on the surface

### Assistant:

KEYWORD: For
VARIABLE: reflectance
CONDITION: is the ratio between the power per unit surface area emitted by a surface and the power per unit surface area (irradiance) incident on the surface
CAUSE_1: a given spectral value
EFFECT_1: reflectance is the ratio between the power per unit surface area emitted by a surface and the power per unit surface area (irradiance) incident on the surface


### END
