I noticed too that some bulbs are hard to find as a 4ft T8, the famed GE Aquarays 9325K amongst them. 3ft T8, but 4ft T12. Wonder why?
From what I personally have observed combined with the opinions of other aquarium professionals is the use of gray nylon filter placed over standard daylights (T2, T5, T8 CFL, etc.) can work as a moonlight; even low level "white" lights such as nightlight bulbs, or even the Rio Mini Sun LED lights can work just fine for this since this has shown to be a more of a low level light issue and timing issue.
Generally around 13 mm in diameter. This is a mini pin bulb which generally uses even less watts per lumen than many than T-8 bulbs. T-5 lamps range from 65 to 105 lumens per watt. The T5 became very popular in the early 2000s among both plant keeping freshwater aquarists and reef keepers for good reasons; they are compact, come in MANY varieties and high lumen per watt outputs (as a broad generalization only requiring 2 to 4 watts per gallon for more shallow planted/reef applications depending upon tank depth and other factors). While the T2 was the latest in straight tube fluorescent lights, the T5 still is better suited for aquariums over 20 inches in depth. The T-5 also comes in many more different varieties, sizes, and even "qualities" (such as the premium Giesemann), and thus is the preferred option for most
Light Bulbs Etc, Inc. 30 Watt 18" T8 2 Pin - Aquarium Super Actinic
Aquarium Lighting: Fluorescent Bulb Selection Guide
T8 fluorescent light bulbs have a smaller diameter than the T12 lighting system. Despite the sizing difference of the two bulbs they still put out roughly the same amount of lumens. Because of the smaller diameter of the T8 bulbs, more of them can be packed into the same canopy than the T12 bulbs. This is a preferable solution for larger, deeper aquariums because it results in an overall brighter illumination making it perfect for plant life, corals and invertebrates.I have larger tanks and use the GE 6500 K aquarium plant bulbs from the local hardware store. I wait until they run a sale on a three pack for around $15.00 to $20.00 for the 48 inch T8s or T12s. My Java fern and Anubias coffeefolia plants grow pretty well in the shaded areas of the tanks.T12 light fixtures run with magnetic ballasts which is less energy efficient than the T8 option that runs with electrical ballasts. The magnetic ballasts cost more to operate than electrical ballasts and can be quite a bit noisier while running. The T8 light bulbs run cooler and provide superior light and color quality. This allows for a more natural lighting in the aquarium than can be provided by the T12 light bulbs.Of the 4 UVB products being discussed, Linear Fluorescent Lighting has been around the longest. These linear fluorescent bulbs will fit into most fluorescent fixtures that accept T8 bulbs, from common aquarium hoods to shoplights purchased from your local home improvement store. Linear fluorescents do a good job of producing low to moderate levels of UVB with a decent CRI, and provide decent even illumination across a wide area (up to 48"). While not the strongest UVB producing bulbs on the market, Linear Fluorescent UVB bulbs definitely have their place, and are great for use with animals that have low to moderate UVB needs and can bask within 12-20" of the bulbs. As a general rule, replace Linear Fluorescent UVB Bulbs every 6 months, although many manufacturers suggest these bulbs remain usable for 12 months.