LEDs are made by a process that deposits the junction materials on a substrate material. One of the limitations of LEDs is that imperfections in the material deposited on the substrate reduce the efficiency. Improvements in the manufacturing process have given us brighter LEDs, as have new junction materials.

To an extent, you can also make the junction larger to get more light. But you can’t extend that very far, mainly due to those imperfections. Their accumulated effect prevents a junction from growing much bigger than a square millimeter. So we won’t likely see larger LED junctions without some advance in materials science to overcome that limitation.

Since a single LED is a relatively low power device (by comparison with other light sources), constructing LED arrays is attractive. As of 2004 you can buy commercial LED arrays for replacement of incandescent lamps. These arrays can deliver as much light as a 20-30 Watt incandescent lamp would. Larger arrays can be constructed for special applications.