Upgrading to High-Intensity Fluorescent (HIF) Lighting for High-Bay Applications

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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
per watt

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

69

1.24

85

50-watt high-pressure sodium

65

0.76

49

2,900-K warm white fluorescent

65

0.98

64

Daylight fluorescent

55

1.72

95

35-watt high-pressure sodium

55

0.57

31

5,000-I 90-CRI fluorescent

46

1.70

78

Vitalite fluorescent

46

1.71

79

Deluxe mercury vapor

40

0.86

34

Standard incandescent

15

1.26

19

Tungsten halogen

22

1.32

29

How to calculate cost-effectiveness

Many factors determine the cost-effectiveness of fluorescent lighting as compared to HID, including:

·         hours of operation

·         cost per kilowatt-hour

·         lamp life

·         lumen depreciation

This lighting calculator can help you compare the costs of HID lighting to fluorescent alternatives. Choose alternatives that provide comparable amounts of light. The calculator corrects for pupil lumens. This factor is not universally accepted, so if you would prefer to perform the calculations without factoring in pupil lumens, input values of 1.0 in the conversion factor field.

Looking ahead

HID and HIF high-bay lighting technologies continue to advance. Expect to see higher efficacies, even lower lumen depreciation numbers and more dimming options to name a few. Higher lumen packages and lower sensitivity to temperature variations are likely for HIF lighting. Also, improved controls and wireless technology will improve the effectiveness of both HIF and HID systems into the future.

On the HID side, count on seeing advanced electronic ballasts and better color quality. While advancements in HID lamps and ballasts may eventually make these systems as energy efficient as HIFs, they may never match the warm-up and restrike times. These delays significantly limit the use of occupancy sensors and similar energy efficient switching methods. HID lighting also has significantly higher lumen depreciation values than T5 lamps. Until these shortcomings can be addressed, HIF remains the best choice for the majority of high-bay applications.

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