棚室内湿度大，光照弱，光照强度减半；
而建造这类养殖设施也有很高的技术要求，即只能让适量的光照透进容器 —— 光照过强或过弱都会降低藻类的生长速度。
They must also be constructed so that the right amount of sunlight hits them—too much or too little slows growth.
如果一个光源照亮某一个地方，这个地方距离光源越远，光照强度会越弱，但是光照强度并不是与光源距离等比例地减弱，就是说，距离延长两倍，光照强度并不是减弱两倍，而是减弱两倍的两倍，等于减弱四倍；
If a light illuminates a certain space, its intensity at twice the distance is not twice as feeble, but two times two, equal four times, as feeble.
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