No extra glass for mogul bulbs needed.
Folks usually add actinics to make their tank look bluer when using bulbs thqt are either too yellow or too green, although there is some speculation thqt it also enhances growth and true coloration (as opposed to perceived coloration while these VHO bulbs are on) of some exotic
Acroporiids. However, true presentation of true color can be acheived in the 10kK to 15kK coor range for many MH bulbs on the market now, with little fluorescence from actinic-type bulbs. Note the color difference between the Iwasaki bulb on the left and the two XM bulbs in the photo below, color temp of the bulbs is 6.5kK for the Iwasaki, 10kK for the XMs, both are 250 watt bulbs on new generatioin Icecap electronic ballasts, pix about 15 months ago in the 180 display tank:
I am not currently running the
VHO actinics on a regular basis, although I think I may start running them again, simply because I like the fluorescence of these bulbs on some corals. Visual presentation of the XM bulbs at 10kK is more than satisfactory for me, and although the PAR for the 250 watt
Iwasaki bulbs is high, I prefer the whiter light (bluer actually) of the XM's and their PAR values on the Icecap Electronics (see Sanjay's work for the actual numbers).
The following shot is of the hood I built for my lighting so I can hide the lighting with a finished look and still be able to vary the height of the bulbs from the surface of the water:
I have fixed the lights on racks that can be adjusted both up and down for height, as well as be totally removed from the hood for cleaning, maintenance, and work inside the tank should the bulb and reflector positions become a hinderance. Cooling fans are set in the top of the hood to push air into the hood to allow for a rolling effect of air inside the hood. This rolling air current must travel across the surface of the water just prior to being ejected from the hood at the surface level of the water column (vents are located along the entire length of the cabinet at the base of the hood in the back). This maximizes evaporative cooling while minimizing direct air current on the bulbs themselves (which prolongs the bulb life).
Interior detail:
You can see the vents at the back of the hood in this photograph. If you have jumpers, place eggcrate in these openings. The fluorescent reflectors mount on the suspended bar at the front of the rack and are aimed to reflect back into the tank at 45 degrees of declination from horizontal. To give you a sense of scale, the muffin fan seen in the upper left corner is 4"x4". The entire front and top of the hood open as one piece, hinged across the entire rear top lip with a stainless steel piano hinge coated with clear marine grade epoxy sealant. All exposed screws and fasteners are either caulked, sealed and painted or made of rust-resistant or sealed stainless steel. This is necessary for all your metal fasteners (screws or nails) to prevent them from rusting inside the wood and allowing the structure to collapse.
The use of glass covers for HQI bulbs would only be necessary for the local enclosure to prevent UV leakage into the tank and the room where the tank is located (just around the bulb and reflector like a closed shield). Covering the entire surface of the tank would both throw off pH, air to water gas exchange, and ultimately, your alk concentrations as the accumulation of CO2 in the tank exerts its effects on the system.
HTH
Vince aka VINNIE 
