As the ratio of height between (light to working plane distance) and (distance between lights) changes the eveness of lighting level on the working plane between those lights changes.
This is perhaps easier to visualise by imagining street lights in an fairly poorly lit area. The light are quite powerfull and set quite high above the ground but also very far apart compared to the height of the lamps. Resut is lighting level on the working plane (the floor level) varies from very bright below each lampost but much darker midway between the lampposts.
Now compare this with a classrom or corridor where the lights are less bright and located much closer tothe floor level but also far more closely grouped along the corridror. Result is a more even lighting level in the classrom or corridor.
An area can be lit with few bright lights spread out which results in uneven lighting levels but can also be lit by the same amount of light but with fewer more evenly spaced fittings which results in a more consistent levelof light such as would be wanted in a classroom.
To investigate set Candela to 5000cd, two lights at 10m height and 20m apart, click the Total checkbox and slide the purple dot between the two fittings and see how the lighting level varies from 54.47lux directly beloww each fitting to a low of 35.36lux at the exact midpoint. A slight variation.
Now slide the red dot upwards to just 3m vertical difference between light and floor level and not how the lighting leven variesfar more (26.36lux) at the midpoint but (557.37lux) directly below either light fitting. Far more variation.
