Bioreactor

1. A production facility comprising:

a plurality of trays;

for each tray, a layer of liquid having a surface, each tray being in receipt of the layer for which said tray is provided, the trays being spaced such that each layer has associated therewith a respective headspace; and

light sources for each layer and which are disposed in the headspace associated with said each layer, to illuminate, at least in part, said each layer,

wherein the light sources are defined in part, by light pipes which receive sunlight in use, each of said light pipes terminating in an emitter; and

the light sources are further defined in part by lamps which deliver artificially produced light.

2. A production facility comprising:

a greenhouse;

a plurality of trays disposed in the greenhouse in stacked, spaced relation to one another such that each tray has associated therewith a respective headspace;

a plurality of layers each containing water, nutrients, dissolved carbon dioxide and algae, the layers being provided one for each tray such that each tray is in receipt of the layer provided therefor; and

light sources disposed in the headspaces, each light source illuminating the associated layer beneath, said light sources comprising LED lights,

wherein said light sources are adapted such that, on a dark night, each light source illuminates the respective layer beneath through the full depth of the layer; and,

said trays decrease in size as the stack progresses upwardly.

3. A production facility according to claim 2 , wherein the trays define a generally conical stack.

4. A production facility according to claim 2 , wherein the tray size and spacing is such that, over the course of a sunny day, at least a majority of the surfaces of the layers are exposed to sunlight.