In his neverending quest to life off the grid, Mikey Sklar made a LED grow lamp from some LEDs, a power supply, and an old broiler pan, which functions as a heat sink. Mikey writes:

A 33 watt grow light made from 19 blue and red LEDs. Each LED is glued onto a broiler pan which acts as a heat sync. This light should be excellent for growing many forms of plants and algae. It cost me about $113 in parts and shipping to make this unit. I estimate this light to be equivalent to a 300W HID/HPS grow light.

Nice process photos and materials/suppliers list included.