Light Output

Increasing Light Emission

[http://www.ncbi.nlm.nih.gov/pubmed/12234677 Paper on isolation of G-LRE and H-LRE, which lists previous attempts to improve light production]
[http://www.ncbi.nlm.nih.gov/pubmed/10036167 Intensified light emission in presence of low ATP concentration by PPDK]
[http://www.ncbi.nlm.nih.gov/pubmed/1332531 Enhanced luciferase activity through cytodine nucleotides]
[http://www.ncbi.nlm.nih.gov/pubmed/12044905 Gene chimerisation to improve practical usefulness of firefly luciferase]
[http://www.ncbi.nlm.nih.gov/pubmed/17540326 Genetically modified firefly luciferase - the EPIC luciferase]

The [http://en.wikipedia.org/wiki/Candela Candela] measures how much light perceivable to the human eye is being emitted by a source of radiation, the Luminous Intensity (or luminous flux. It is related to [http://en.wikipedia.org/wiki/Radient_intensity Radiant intensity] (or radiant flux) (which is measured in watts per steradian) but has been weighted by a [http://en.wikipedia.org/wiki/Luminosity_function Luminosity function]. This alters the power output so that it is proportional to the sensitivity of the human eye: [http://en.wikipedia.or/wiki/Candela#Explanation Definition] of the candela with respect to Radiant intensity. Therefore, an object which is black may be emitting a lot of radiation (measured in watts per steradian) but since it is not perceivable to the human eye it is emitting 0cd of radiation.
The [http://en.wikipedia.org/wiki/Lumen_%28unit%29 lumen] is simply cd*sr. It is thus the analogue to the Watt

The [http://en.wikipedia.org/wiki/Lux Lux] measures how much light is incident on a suface, the Illuminance. It is related to irradiance (measured in Watts per m^2) but has been weighted again by the luminosity function. 1lux=1cd/m^2
The luminance of an object is how much light is emitted from it. This is also measured in Lux, but it is different contextually.

A table of ambient illuminances. For our glowing bacteria to be seen from a given distance, they must be at least 1/20th of this value.

Illuminance	Example
10⁻⁵ lux	Light from Sirius, the brightest star in the night sky
10⁻⁴ lux	Total starlight, overcast sky
0.002 lux	Moonless clear night sky with airglow
0.01 lux	Quarter moon
0.27 lux	Full moon on a clear night
1 lux	Full moon overhead at tropical latitude
3.4 lux	Dark limit of civil twilight under a clear sky
50 lux	Family living room
80 lux	Hallway/toilet
100 lux	Very dark overcast day
320–500 lux	Office lighting
400 lux	Sunrise or sunset on a clear day.
1,000 lux	Overcast day
10,000–25,000 lux	Full daylight (not direct sun)
32,000–130,000 lux	Direct sunlight

A brief [http://en.wikipedia.org/wiki/Candela#SI_photometric_light_units summary] of the different luminous measures

To summarise, the luminosity function allows one to convert between radiant energy and luminous (i.e., visible) energy.