Hello, I would like to build a panel light with four flourescent tubes. The tubes have a diameter of 26 mm and are 1200 mm long. They have a distance of 42 mm one to another. The tubes are mounted on a board, that is covered with aluminium foil as a reflector. Each tube produces a luminous flux of 2340 Lumen. I would like to calculate the illuminance in Lux in one meter perpendicular distance of the panel light. How can I do that ? The result does not have to be perfect – a result within 10 – 20 % of the actual value would be satisfactory.