Adding a personal 2¢ to the previously posted Messages...
What is the lowest temperature at which a T8 lamp will operate?
How much light do they produce at sub-zero temperatures when they don't operate properly?
I have mentioned the following scenario before, so in the spirit of redundancy I proudly mention it again!
Per the Design-Build of a large Industrial Cold Storage Warehouse, an Illumination Maintenance follow-up was performed by myself and another EE. The tasks involved taking Foot-Candle readings at various points / locations, at a work plane of +2.5 Feet above Floor level.
Target Ambient Temperatures per Function Area:
A: Loading Dock: 4.4°C (40°F) Apx. 15,000 Sq. Ft.
B: Cold Storage; Warehouse Freezer: -20°C (-4°F) Apx. 65,000 Sq. Ft.
C: Cold Storage; Spec. Freezer: -40°C (-40°F) Apx. 1,000 Sq. Ft.
Per Design, the Installed Lighting for the Loading Dock and the -20°C Warehouse Freezer was built around our typical F54 T5HO 5000K Lamps, installed in 6 Lamp High Bay Fixtures, driven by Programmed Start Ballasts.
400 Watt Pulse Start Metal Halide High Bay Fixtures with Magnetic Reactor Ballasts, were used in the -40°C Spec. Freezer
Several Months after Final Commissioning and Start-up, the Client's Maintenance Staff installed several Eight Foot Fluorescent Reflector Strips in the Loading Dock and the Warehouse Freezer.
These Luminaries used T8 Standard Medium Bi-pin Lamps (265ma-430ma) with 4100K Color Temperature, driven by standard Electronic Instant Start Ballastry.
A mixture of Luminaries using (4) Four-Foot F32T8 Lamps, or (2) Eight-Foot F96T8 Lamps had been installed in both areas.
At the 40°F Loading Dock, the Quantity of Light Output for the T8 Fixtures was noticeably lower than the "Perceived Normal Output" of a given F32T8, 4100K Color Temp.
There was at least a 25% reduction in output Lumens from the T8 Cold Cathode Operation in the 40°F Ambient, as evident by Foot-Candle readings, and in comparison with an equivalent Lamp operated in a nearby Office; where the Ambient was +70°F.
The F54 T5HO High Bays were performing at, or better than our original target design prediction of 35Fc avg.
Quite impressive for Fixtures in operation for 18 Months! Lumen depreciation was less than expected, but this Facility is for Food-Based Logistics, so routine Maintenance keeps the dust from building up.
BTW, the T5's were Ceiling mounted at +24 Feet A.F.F., and the T8's were Chain Suspended at +10 Feet A.F.F., so the T5's likely had more Heat surrounding the Fixtures.
Lamp operation at the -20°C Warehouse Freezer was much different for the T8 Lamps, but the same for the T5 Lamps.
The T5 High Bays operated as per design, with a target of 30Fc avg.
The T8 Lamps could not achieve a stable Lamp Plasma in this very cold Ambient, and as result, suffered from Hypothermia.
Clear indications of this were the extremely low Lumen output (at best, 10% rated Lamp Lumens), and the constant "Cork-Screw Swirrel" of Gases springing across the Lamp.
As to mounting heights, the T5's were Ceiling mounted at +40 Feet A.F.F., and, as with the Loading Dock, the T8's were Chain Suspended at +10 Feet A.F.F.; so once again, the T5's likely have more Heat surrounding the Fixtures due to their mounting height and location, than the T8 Fixtures would have.
The warmer, lighter Ambient Air being at Ceiling Height (Buoyant forces plus Solar Heat Gain), and the colder, heavier Ambient Air settling close to the Concrete Slab Floor.
FWIW, the output Lumens from the 400W MH in the Spec. Freezer was reduced apx. 30% by the extremely low Ambient Temperature.
Some important points here are:
- Cold Cathode (Instant Start) Lamp Operation was used to drive the 265ma - 430ma T8 Lamps in the Suspended Strip Fixtures,
- Hot Cathode Lamp Operation - via Programmed Start was used with the T5 High Bay Fixtures,
- In addition to the Hot Cathode Lamp Operation, High Output or "HO" (800ma) Lamps were used in the High Bay Fixtures,
- Area Lighting for the High Bays was divided into separate Occupancy Sensor Controlled Zones, where Four of the Six Lamps were turned Off after 30 Minutes of inactivity.
The outer Two Lamps remained On until the end of the work day (16 Hours On, 8 Hours Off via Lighting Control Time Clock).
Man, that Warehouse was COLD!!! We would periodically run out to the 40 degree Loading Dock to warm up!!!