Well you can use this little snippet I pulled from another post around here somewhere and depending on how much lux the fluorescents use they may be better in the GH.
Daylight intensity in different conditions
Illuminance Example
120,000 lux Brightest sunlight
110,000 lux Bright sunlight
20,000 lux Shade illuminated by entire clear blue sky, midday
10,000 - 25,000 lux Typical overcast day, midday
<200 lux Extreme of darkest storm clouds, midday
400 lux Sunrise or sunset on a clear day (ambient illumination).
40 lux Fully overcast, sunset/sunrise
<1 lux Extreme of darkest storm clouds, sunset/rise
Daylight intensity in different conditions
Illuminance Example
120,000 lux Brightest sunlight
110,000 lux Bright sunlight
20,000 lux Shade illuminated by entire clear blue sky, midday
10,000 - 25,000 lux Typical overcast day, midday
<200 lux Extreme of darkest storm clouds, midday
400 lux Sunrise or sunset on a clear day (ambient illumination).
40 lux Fully overcast, sunset/sunrise
<1 lux Extreme of darkest storm clouds, sunset/rise