threshold exposure meaning in English

临界曝光
照射阈,曝光阈

Because the threshold exposure levels for photic damage to the retina at each wavelength of the optical spectrum are well known , it is fairly simple to calculate the maximum permissible filter transmittance that will provide adequate retinal protection from sunlight
由于每种波长光线的极限值都已被测定,所以要计算出安全太阳滤镜最高允许透光率是很容易的