T-12 versus T-8 Lamps:

		If existing luminaires utilize T-12 lamps, and the designer is considering a ballast 
		replacement, then the following advantages/disadvantages of specifying T-8 ballasts and 
		lamps should be considered:

	·	32 watt T-8 lamps typically provide fewer lumens than 40 watt T-12 lamps, but 
		provide more lumens per watt and can increase luminaire efficiency.  The efficacy 
		(lumens per watt) differs depending on lamp/ballast combinations.

	·	T-8 lamps are smaller in diameter (1") than T-12 lamps (1.5").  Consequently, they 
		can provide tighter beam control with a reflector designed for them.  They also use 
		less rare-earth phosphors, thereby considerably reducing their cost relative to T-12 
		rare earth phosphor lamps.

	.	A wider variety of ballast output options is available for the T-8, allowing the 
		designer to more closely meet target footcandle levels.

	·	The reduced size can also result in increased surface brightness, which could 
		increase the potential for glare in open cell luminaires.

	·	While a retrofit from T-12 to T-8 lamps does require changing the ballast, it does 
		not require changing the lampholders.  Lampholders over ten years old, however, 
		should be replaced to assure a tight fit with lamp pins.  It should be noted that a 6" 
		leg spacing is available in a 31 nominal watt T-8 U-lamp, simplifying conversion 
		of 2x2 luminaires with T-12 U-lamps.