T5 fluorescent lamps

Q1) What are T5 lamps?

T5 lamps are fluorescent lamps that are 16mm (5/8") in diameter. These lamps are approximately 40% smaller than T8 lamps, and almost 60% smaller than T12 lamps.


Q2) Are T5 lamps the same length as T8 lamps?

T5 lamps are slightly shorter than T8 lamps for similar rated power. Therefore they cannot be used as replacements in large lamps. However, some luminaires can be made to accept either T5 or T8 lamps by changing the sockets and ballasts. Please refer to the Plug and Enhance Technology for the replacement of T8 lamps by T5 lamps.


Q3) What are T5 HO lamps?

"HO" stands for high output. T5 HO lamps deliver more light than standard T5 lamps and are available in higher wattages. HO lamps have the same diameter and length as standard T5 lamps. The following table compares characteristics of T5 and T5 HO lamps.

Lamp type Nominal length (inch) Rated light output (lm) Lamp efficacy (lm/W)
T5 14W 22 1350 96
T5 21W 34 2100 100
T5 28W 46 2900 104
T5 35W 58 3650 104
T5 HO 24W 22 2000 86
T5 HO 39W 34 3500 90
T5 HO 54W 46 5000 93
T5 HO 80W 58 7000 88


Q4) Do T5 luminaires perform better than T8 luminaires?

The lamp size and optimal temperature of T5 lamps are different from that of T8 lamps, and both these factors affect luminaire performance. The optical control efficiency and flexibility of luminaires for T5 lamps is better because of the smaller diameter of the lamps. The higher optimal temperature of T5 lamps may allow T5 lamps to perform better in closed luminaires than open luminaires.


Q5) How does temperature affect the performance of light output of T5 lamps?

T5 and T5 HO lamps produce maximum light output at 35oC, while the light output of T8 lamps is optimal at a temperature of 25oC. The figure below illustrates the variation of light output of T5 and T8 lamps at different operating temperatures. There are many factors might also influence the light output of T5 lamps. The difference in light output of T5 lamps between 25oC and 35oC is always smaller than that shown in the figure below by some research studies.

Relationship between light output and ambient temperature. The text above describes the image.


Electronic ballast

Q1) What are the differences between electromagnetic and electronic ballast?

Electromagnetic ballasts employ copper coils and transformers to run a lamp. They are usually consists of a choke and a capacitor for power factor correction. Electronic ballast involves low-pass filter, rectifier, buffer capacitor and a high frequency oscillator. Electromagnetic ballasts cost less, but are less efficient than electronic ballast. Using electronic ballasts in fluorescent lamps can enhance significantly system efficiency as well as enhancing light output quality.


Q2) Do fluorescent lamps flicker with electronic ballasts?

Since electronic ballasts work with higher frequency than electromagnetic ballasts, their flickering effect is minimized.


Compact fluorescent lamps (CFL)

Q1) How does the lamp life of CFL compare to other light sources?

Rated lamp life of CFL ranges from 8,000 to 10,000 hours. Rated lamp life for other lamp technologies varies, from 1,000 hours for filament lamps to around 60,000 hours for induction lamps.


Q2) What CFL should I buy to replace the corresponding incandescent bulbs?

CFLs use about one-forth of the power of incandescent bulbs to give the same amount of light. Therefore the rated power input of CFLs is much lower than incandescent bulbs. Please refer to the table which shows the equivalent light output of CFLs compared with Incandescent bulbs.


Light Emitting Diode (LED)

Q1) What is the efficiency of LEDs compared with other light sources?

Efficiency of a lamp is called luminous efficacy, which is defined by the luminous flux in lumen per unit lamp power. The table below compares the typical luminous efficacy and life expectancy of different colours of LEDs commonly available in the market with conventional lamps.

Light sources   Luminous efficacy (lumen/W) Life expectancy (hours)
1W LEDs Red 37 50,000
Red-orange 48 50,000
Amber 37 50,000
Green 40 50,000
Cyan 34 50,000
Blue 12 50,000
White (phosphors-converted) 34 50,000
White (colour blending) 30 50,000
Incandescent lamp 9 3,000
T8 Fluorescent lamp 70 12,000
T5 fluorescent lamp 90 18,000
Integrated compact fluorescent lamp 55 6,000
Integrated Induction lamp 70 60,000


Q2) What are the possible applications of LEDs?

LEDs have a wide range of applications because their robust and versatile characteristics. Here are some application examples of LEDs:

  • Exit sign
  • Building facades lighting
  • Traffic signal
  • Areas with high lamp replacement (maintenance) cost
  • Projector
  • Landscape lighting
  • Vehicle rear light, torches, table lights, decorative lamp etc.


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