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The T8 is among the most efficient fluorescent source. In addition, their cost is now lower than the costs for T12 lamps.
T8 lamps are available with three different types of phosphor coatings:
- Coating with halo-phosphate phosphors: The halo-phosphates have been used for many years, but have the disadvantage that good colour rendering can only be achieved at the expense of reduced efficacy. Colour rendering ranges from 50 to 75.
- Coating with three-band phosphors (or tri-phosphors): these phosphors achieve both good colour rendering and high efficacy; however they are more expensive than the older halo-phosphates. Colour rendering ranges from 80 to 85.
- Coating with multi-band phosphors: very high colour rendering, but this has only been achieved with some reduction in efficacy compared with the tri-phosphor lamps. Colour rendering of 90 and above.
During the life of a fluorescent lamp, the phosphors age and the light output decreases.
The two latter coatings age more slowly than the halo-phosphates; these lamps therefore have improved lumen maintenance.
The halo-phosphate type 26mm lamps produce approximately the same light output as the 38 mm diameter lamps of the same length and colour, but consume around 8% less energy. The Tri-phosphor type version not only consumes around 8% less energy but also produces approximately 10% more lumens and has a higher Colour Rendering Index. This latter version shall therefore be preferred.
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