T5 Temperature Performance

T5 Temperature Performance

There is much confusing information regarding operating temperature ranges for the T5HO lamp. Most fluorescent lamps (T12, T8) were designed to provide their maximum light output at an ambient temperature of 25°C (77°F). The T5HO lamp is designed to provide maximum light output at 35°C (95°F). Note that these are not room ambient temps, but rather they are the ambient temperature in relation to the bulb wall. Major lamp manufacturers exhibit the curve below to show effective lumen output at certain temperatures, but they neglect to inform that these are estimates based on a bare lamp in free air, not an operating lamp in a luminaire, especially an enclosed luminaire. This leads to a misunderstanding.

light output vs temperature


T5 Lamp Performance is Optimized at 35°C
The chart above indicates that the T5 system will not produce much at 5°C(41°F), yet the T5HO ballast/lamp combination is warranted to start and operate reliably down to -20°F(-30°C)! Obviously something is inconsistent here.

The Light Edge luminaires have been used successfully in nearly every conceivable cold weather application, from open parking structures in Calgary & Anchorage, to frozen food lockers and cold storage facilities. How is this possible? Simple...all of the T5HO fixtures provided by The Light Edge are enclosed systems, which provide the best lumen maintenance regardless of the ambient operating temperature.


The Light Edge has performed testing of our 4-lamp MONSOONTM luminaire in a  -26°C(-15°F) freezer environment. The MONSOONTM units were installed and allowed to stabilize at (-)15°F for 4 hours, then energized. The units started and came up to maximum light output within 3 minutes.

After burning for several days (approx. 120 hours, allowing full lamp seasoning) a Fluke ET995 digital thermometer instrument coupled to a Fluke 80tk thermocouple was inserted into the lamp compartment and the following readings were taken:

  • Room Ambient Temperature: -15°F (-26°C)
  • Inside surface of lens: 15°F (-9°C)
  • Lamp hot spot: 71°F (22°C)
  • Ambient lamp compartment: 67°F (20°C)

According to data published by major lamp manufacturers (relationship of luminous flux to ambient temperature), the T5HO lamp operating in an ambient environment, in still air, of -20°C doesn't register on the chart. However, the lamp compartment temperature in an enclosed luminaire is higher than the room ambient temperature. In our example above, with a corrected ambient temperature of 67°F, the efficiency of the lamp output is raised to 76%. All light sources will suffer some loss at such an extremely low temperature, however the T5HO lamp shows itself suitable as long as it is in an enclosed luminaire within that environment. The majority of the applications we anticipate are in an environment range above 32°F, which as the (incomplete) manufacturer's data projects should allow at least 83% efficiency.

The chart below shows relative relationship between room ambient temperature (in Fahrenheit) and light output for our enclosed luminaire. It is a compilation of lamp manufacturer's data (also attached) and our studies.

light output vs temperature



T5 technology has a very broad range of operation - one simply needs to address the technology correctly. The Light Edge utilizes extremely efficient heatsinking in our products. Heatsinking is 60% more effective than convective airflow for ballast cooling, and doesn't pull cold air or dirt through the fixture (keeping the fixture clean and lumen output high!). As an illustration of the impressive thermal management of our luminaires, let's look at an installation for US Gypsum in Washington State:


The customer built custom louvered galvanized shielding around The Light Edge RAPTORTM 2-lamp luminaires that illuminate the viewing ports on their gypsum-drying kilns. These shields were neccessary for worker protection, because the surface temperature of the RAPTORTM tests to an incredible 82°C (180°F)! Although far beyond the ballast manufacturers warranty for heat (and The Light Edge's as well!), these RAPTORTM luminares have been operating without failure for over two years.

That's good thermal attenuation!