Mercury vapor lites AND shop light question for "the George"

> From: Earle Hamilton
> A recent digest mentioned mercury vaport lite (175 watt) at about
> sixty bucks.  Saw an add for one at a local hardware store for only
> thirty bucks.  Is anybody out there using mercury vapor lites.  What
> are the pros and cons of using them compared to MH.

Are you sure they are mercury vapor and not *sodium* vapor?  MV are
almost as expensive as MH, I think.  I also think they are just about
the same except that MH has some halides of metal added for a better
spectrum.  SV are very cheap but have a lousy spectrum.

> George, I saw in a post you made some time back that we should not use 
> the cheap shop lights.  Did I miss something?  What is wrong with buying 
> a ten dollar double bulb 4' fixture at the discount store?

There's nothing inherently wrong with buying them.  It's the
application of them to aquariums that I take issue with <g>.

1) The fixtures don't seem to be long lived. 
2) The sleazo electronics reduce the light from the FL bulbs by about
   20%.  Maybe not a big deal to you, but when I pay $20 for a tri-
   phosphor bulb, I want all the lumens I paid for.  The bulb will
   loose 10-20% over 6 months anyway, why *start* with lower lumens?
3) The sleazo fixtures seem to greatly shorten the life of some bulbs,
   most notably Tritons.  Consumer Reports noted this same thing when
   they tested compact FL bulbs that are designed to replace incand.
   bulbs - some electronic ballasts greatly shortened the bulb life. 
Other than that, they are great. 

> Bought one of those cheap lux meters ($40) and was surprised at the 
> values being so low, especially in the non MH lit tanks.

I wonder how it compares to the $120 digital unit I got from a reef
place?  I have an expensive camera light meter and it's lux reading
does not match the luxmeter.  A cheap meter I saw in a hydroponics
store matched neither one.  The luxmeter seems to agree with rated
lumens of some bulbs ...

> I suggest we consider these underwater light meters to 
> shed some light :) on the most important variable in making plants grow 

mega dittos (to borrow a phrase).