Lighting Intensity

To: ESCHOVIL <ESCHOVIL at us_oracle.com>, Aquatic-Plants <Aquatic-Plants at actwin_com>
Subject: Lighting Intensity
From: Rodney Dorville/EC/SP_SF <RDORVILL at sp_ac.sg>
Date: 3 Feb 97 12:52:43 WAT

>> Question One:  Is it true that the intensity of MH is the same as 4 
flourescents at the surface
>> of the aquarium?

Assuming that the Metal Halide bulb is 150W and is of the minature type, the 
luminous flux on the surface is 11250 lux with a colour temperature of 4200K 
over 1m square
For a flourescent tube 36W cool daylight (normal) it is about 2500 lux, so 4 
tubes = 10000lux.  However, with a flouro system you can vary the colour 
temperature ranging from 4000K to 6500K by having one bulb in a particular 
temperature (assuming normal bulbs - not the grow-lux, actinic-sun or 
power-twist versions).
So approximately, you will get the same lighting at the SURFACE of the water.  
The power consumption is, however, different with the Metal Halide taking about 
300W in all (heat, ballast etc) and the flouros - 180W in all (heat, ballast 
etc).


>> Second Question:  If question one is true, does one form of light penetrate 
water better
>> than the other?  IOW, should a tank that is lit by flourescents be more 
intensly lit at the
>> same depth as light from a MH bulb?

The light penetration of a MH with proper reflector can reach up to 36 inches 
easily, however, no matter how many fluorescent lamps you have, the maximum 
penetration is about 18 inches.  Again, if the bulbs are placed at the surface 
of the water.  This can be easily measured, as you have mentioned, with a lux 
meter.


>> Does this seem accurate, or does everyone think that I was smoking my 
aquatic plants?  Could this
>> effect have been caused by the type of reflector or the differences between 
MHs and
>> flourescents?

A reflector helps immensely.  A deep reflector for a MH lamp will increase your 
intensity by at least 40-60%.  For fluorescent lamps, however, reflectors help 
up to 30%.  Close proximity of flourescent lamps decrese the intensity because 
of adsorbtion effects.

Rodney