Rather than hijacking a thread where #12 posted about rpm cube rule............. Does anyone know how much to increase lumen output to double light level? 4 times? Square rule. Cube? Ignore the details if possible. Just ball park. Over head light (high bay) outputs 120 degree pattern. For example. If I have a 5,000 lm source now and want to double the light level in the area covered by the 120 degree pattern. More questions to follow if there's an expert here.