Today's HID fluorescent fixtures designed for high-bay (high-ceiling) applications have many advantages over comparable HID fixtures:
· reduced energy consumption
· lower lumen depreciation rates
· more dimming options
· faster start-up / restrike
· better color rendition
· more pupil lumens
· reduced glare
These benefits add up to real cost savings over the life of the product. As an added bonus, HID fluorescents do a tremendous job of lighting large spaces.
High-intensity fluorescent fixture designs
As you'll see below, the majority of today’s HIF fixtures employ T8 or high-output T5 linear fluorescent lamps. These tubes last longer, are most efficient and have lower lumen depreciation than twin-tube lamps and compact fluorescent lamps (CFLs). Their innovative reflector designs make HIFs ideal for any ceiling height, so they are an excellent replacement for HID lamps.
HIF fixtures are typically square or rectangular, although an alternative design has been shown to be effective for wide-open spaces. The “star” fixture uses CFLs or twin-tube T5s mounted to 2-foot extensions that radiate out from a central housing that usually contains the ballasts. Its circular light distribution successfully illuminates such applications as skating rinks.
Where HID technology once had a performance advantage with respect to wide temperature ranges, HIFs have caught up. Amalgam technology – where certain metals are mixed with the mercury inside the lamp – enables HIFs to sustain maximum output levels throughout temperature extremes. The one drawback is that amalgam lamps are not dimmable.
How to Make the Best Choice
The Color Rendering Index of fluorescent and HID lamps
The color rendering index (CRI) indicates a light's ability to accurately render a sample of eight standard colors relative to a standard source. Measured on a scale of 0 to 100, the higher the CRI value, the better a light will render color.
Lamp type CRI
T8 fluorescent ..................................... 75–98
T5 fluorescent ..................................... 75–98
High-color-rendering metal halide....... 80–93
White high-pressure sodium ............... 60–85
Standard metal halide ......................... 60–70
Pulse-start metal halide ...................... 65–70
High-pressure sodium................................ 27
Low-pressure sodium ................................. 5
Conversion factors for lumens to pupil lumens
Pupil lumens per watt measures how effectively the eye sees emitted light. We achieve this figure by applying correction factors to conventional lumens per watt values. Pupils are more receptive to light at the blue end of the spectrum.
|
Light source |
Conventional lumens |
Correction factor |
Pupil lumens per watt |
|
Low-pressure sodium |
165 |
0.38 |
63 |
|
5,000-K T5 fluorescent |
104 |
1.83 |
190 |
|
4,100-K T5 fluorescent |
90 |
1.62 |
145 |
|
Clear metal halide |
85 |
1.49 |
126 |
|
5,000-K pure triphosphor fluorescent |
70 |
1.58 |
111 |
|
3,500-K pure triphosphor fluorescent |