Tom's Life Bits

I've retrofitted most of my older fluorescents with electronic ballasts and T8 lamps. To my eyes, the light output appears to be about the same or a bit higher.

This may be partly because I'm comparing new lamps to old ones. Initial lumens of a typical F40T12 “cool white” T12 lamp is around 3000. Initial lumens for a F32T8 4100K T8 lamp is around 2950. So, in theory, a tiny bit dimmer - but T8s maintain their output better over their lives, so a 5 year old T8 will be brighter than a 5 year old T12.

Note that this is the output using ballasts with normal ballast factor. Most standard ballasts slightly underdrive T8 lamps, to about 90% of their rated power (and light output). This is where some of the advertised energy savings comes from (though they really are more efficient at turning electricity into light).

If you want a dramatic increase in light when you fit new ballasts and lamps, specify high ballast factor. This runs the lamps at typically 108-115% of rated power, or around 34-37 watts, and increases output to 3200-3350 lumens.

High ballast factor ballasts can be tough to find, but in most cases you can accomplish almost exactly the same effect by fitting 2-lamp fixtures with 3-lamp NBF ballasts and capping the third output wire.

Your Lithonia fixtures will probably come with NBF ballasts unless you order them otherwise (they'll probably be Advance REL-2P32-SC). You'll lose a few lumens to the diffuser. The new lamps should more than make up for that loss. So, I'd guess that your new light level should be a bit higher than your old T12s.

Assuming you use 4100K lamps, the new ones will also seem brighter, lumen output aside, because of their higher CRI. Old T12 cool white lamps have a CRI around 63; new T8 4100K lamps are usually 78 or 82 CRI. This makes colors look brighter and truer, and whites look less dingy.

Energy Information

Ballasts are available with various ballast factors. Ballast factor is defined as the relative light output compared with a reference ballast. For example, a ballast factor of 0.85 would yield 85 percent of a lamp's rated lumens or light output. Refer to Table 2 for energy usage for various types. Electronic ballasts are typically available in three groups of ballast factors:

• Low ballast factor (LBF) = 70 to 80 percent of rated lamp light output
• Normal ballast factor (NBF) = 85 to 95 percent light output
• High ballast factor (HBF) = 105 to 115 percent light output

Table 2 illustrates the differences in operating costs for a common two-lamp system. The analysis reveals that T-8 lamps combined with an electronic ballast produce approximately 89 lumens of light per watt, whereas T-12 lamps using a standard electromagnetic ballast produce only 54 lumens per watt. The maximum energy efficiency can be achieved by using both premium lamps in combination with premium ballasts. This combination produces close to 100 lumens of light per watt.

Comparison

The combination of lamp and ballast determines the type of light produced. Selecting the right combination starts with knowing the location and purpose of the lighting. After determining the required lighting levels and selecting the appropriate luminaire, the proper lamp and ballast must be chosen. Refer to Table 2 for light output comparison. It should be noted that light outputs are based on initial levels. The lamp lumen depreciation (LLD), at 40 percent of rated lamp life, is 85 percent of initial lumens for a T-12 lamp, whereas the T-8, T-5 and T-5 HO lamps are much better at 95 percent.

In areas with fixed ceiling grid patterns or for a retrofit project, the available options allow you to select the right combination of lamps and ballasts to meet the lighting requirements for the space in the most cost effective and energy-efficient manner.

by Ian Philips

There has recently been a lot of discussion on fluorescent lighting and T8 vs. T12 bulbs. I thought that a summary of the discussion would be of value. I have distilled many postings down to a unified article.

The bottom line was that people who have tried both types of lamps prefer:

       T8 bulbs in combination with electronic rapid start ballast.\\

The benefits being:

       Longer bulb life with lower lumens drop off.
       Significant power ($) savings.
       Cheaper bulbs.