Re: Lighting efficiency

Dave Gomberg writes....

Reply-To: ac554 at FreeNet_Carleton.CA
>On Thu, 29 Jun 1995 03:39:03 -0400 you wrote:
>>  fluorescent T12, GE Chroma 50, 1870 lumens, 40 watts,
>>    46.75 lumens/watt (similar for a cool white)
>>  fluorescent T12, GE rare earth, 2960 lumens, 40 watts,
>>    74 lumens/watt (typical "aquarium" bulb)
>>  fluorescent T8, GE rare earth, electronic ballast (!), 2650 lumens, 27 watts,
>>    98 lumens/watt  (part is T8 and part is electronic ballast)
>>  MH, E37 VBU, 31000 lumens, 400 watts,
>>    78 lumens/watt
>With the figures above, why would anyone go MH? 
>They are expensive, dangerous, and black body at
>best.  Why not go for phosphors tuned to plant
>needs?  I am not saying such a tube exists, but I
>am saying it is the best choice.  Sylvania MUST
>have data on GroLux, it's been out for 40 years.
>Dave Gomberg, Experimenta      San Francisco CA      gomberg at wcf_com

Actually, there are many reasons for going with MH. One may prefer
a spotlight effect, wish to work in the tank relatively unencombered
by an awkward hood, or have a six foot long tank for which the above
fluorescent lamps do not provide a good fit.

I'm also guessing that the lumens/watt of the fluorescents are
initial lumens. There is quite a dropoff generally within a year.
Below is some data from Venture concerning their vertical burn
MH lamps.

Bulb  Watts   Avg. Life       Lumens/watt
                         Initial    At 40% Lifespan
E90   175     10000 hrs     91            76              
E40   400     20000 hrs    100            91

Both of the above lamps are 4000K with CRI 65. I'll guarantee
you there is no fluorescent lamp that with give you 91 lumens/
watt after a 8000 hour burn. I'm not advocating these lamps.
It's just that the choices are not obvious. It depends upon ones
requirements. As for expense, I'm presently using a $28 (Canadian)
Phillips MH that I expect to last two or three years. The colour
could be better, but it fits the bill.