| | Re: Old plant grower, LCD lights, needs heip!
LEDs (light emitting diodes) are point sources of light. Each of them alone is a pretty weak light "bulb", but most LED aquarium lights use dozens of them spread out over a large area. Unlike fluorescent lights they don't need reflectors, and each tiny LED produces a cone of light about 120+ degree cone of light. So, they cover a lot of area with light coming from all directions. Many manufacturers of these light fixtures also measure the light intensity from them at various distances, expressed in PAR dimensions, photons per square meter per second. Look for the intensity at the distance your light will be from the substrate. If that is 20-40 it is low light, 40-50 or 60 is medium light, and above 60 is high light.