FAQs HID – Fluorescent

  1. How is it possible for a fluorescent fixture to replace a HID? For example, how can you replace a 400w Metal Halide, which has 36,000 initial lumens, and still save energy?
  2. What is the difference between standard footcandles and perceived footcandles? How does this affect how I handle High Pressure Sodium retrofits?
  3. What Kelvin Temperature do you recommend in which application?
  4. I have a freezer environment, is there anyway to retrofit this facility with fluorescent and save energy?
  5. When do you recommend T5HO, and when do you recommend T8?
  6. How do I know if lamps are included in a fixture quote?

1) How is it possible for a fluorescent fixture to replace a HID? For example, how can you replace a 400w Metal Halide, which has 36,000 initial lumens, and still save energy?

Although a bare 400w Metal Halide bulb may emit 36,000 initial lumens, we take many factors into account when replacing an existing Metal Halide fixture. First, the fixture body utilized most frequently with Metal Halide fixtures is characterized by a spun reflector and a lens. This combination is not conducive to maximum fixture efficiencies, and most existing HID fixtures have an overall fixture efficiency between 60 and 70%. Optimum Lighting has designed our fixtures with efficiency in mind, and most of our fixtures are over 80% efficient (with many open high bays offering over 90% efficiency levels).

Furthermore, although the initial lumen output of a Metal Halide fixture may be quite high, metal halide fixtures are known for their poor lumen maintenance. The average 400w Metal Halide fixture emits only 65% of its initial lumens by the time it hits Mean lamp life (40% of total lamp life or 8000 hours) and as low as 40% of its initial lumens by the end of lamp life. Fluorescent lamps, on the other hand, have superior lumen maintenance, and maintain 90-94% of their initial lumens through the end of lamp life.

So we calculate the mean lumen output of a 400w Metal Halide as:

Initial Lumens per lamp x Number of lamps x Fixture efficiency x Lumen maintenance x Ballast Factor = 36,000 lumens x 1 lamp x 0.65 x 0.65 x 1.0 = 15,210 mean lumens

We can replace this fixture using a G16 632 UV 2HI E 850 – a 6 lamp T8 high bay with 1.15 ballast factor, which will emit 18,727 mean lumens (2950 mean lumens x 6 lamps x 1.15 ballast factor x 0.92 fixture efficiency). Furthermore, the fluorescent system will require only 218 watts versus the 455 watts required by the 400w Metal Halide fixture – a 52% savings!

2) What is the difference between standard footcandles and perceived footcandles? How does this affect how I handle High Pressure Sodium retrofits?

The human eye is composed of both cones and rods, which work together to process images and light. All traditional light meters are calibrated solely on the measure of photopic light (which is processed by the eye’s cones), as the rod’s response to light was assumed to be arbitrary. Research sponsored by the US Department of Energy, however, has shown that not only do the rods serve an integral role in brightness perception, but they also control pupil size, and thus visual acuity. The source of the rod’s light perception is in their ability to perceive ‘scotopic light’, while cones can only perceive ‘photopic light’. This research suggests that traditional lightmeters that measure only photopic light are outdated, and a more accurate measure of brightness would take into account both scotopic and photopic light (or the S/P ratio of light).

Based on these findings, scientists with the Department of Energy were able to calculate ‘adjustment’ factors for traditional photopically-based footcandles (S/P Graph), which we can use to adjust standard photopic footcandles to a more useful measurement that takes Scotopic and Photopic light into account. For example, a 400w High Pressure Sodium fixture emits an average of 62,025 mean lumens (adjusted for fixture efficiency), but to determine perceived lumens you would need to adjust by a factor of 0.62. The actual lumen output as perceived by the human eye is only 15,516 lumens.

These findings are quite meaningful when retrofitting existing High Pressure Sodium fixtures. If photopic lumens alone were taken into account, an 8 lamp T8 with High Ballast Factor drawing 294 watts would be needed to replace a 400w High Pressure Sodium. Adjusting for scotopic light, however, a 6 lamp T8 drawing 218 watts could easily do the job – saving the customer an additional 76 watts.


3) What Kelvin Temperature do you recommend in which application?

Kelvin Temperature is largely a matter of personal preference. Higher Kelvin temperature fixtures emit a ‘cooler’ blue light, while lower Kelvin temperatures emit a ‘warmer’ red light. Also higher Kelvin temperatures appear brighter than lower Kelvin temperatures, due to the difference in S/P ratio of each. Due to the principles discussed in Question 2, a 4100K Fluorescent, for example, will appear to emit 1.62 times more light than the standardized footcandle readings, while 5000K Fluorescent will appear to emit 1.96 times more light (21% more light).

Lower Kelvin temperatures (3500) are great for restaurant environments, where a calm mood is desired. While 3500 or 4100K are ideal for supermarket and retail applications, as they accentuate the colors (bright red apples, defined product logos) and the appeal of the products. Generally we recommend 5000K lamps for gymnasiums, factories, warehouse and distribution centers. The higher Kelvin temperature maximizes the perceived light in the environment without the ‘blue hue’ that is often characteristic of 6500K lamps. The higher Kelvin temperature is conducive to increased worker visual acuity, productivity, visual perception and even morale. For gymnasium applications where video equipment is utilized, Kelvin temperatures over 5800K should not be used as they can affect the quality of the recording.

4) I have a freezer environment, is there anyway to retrofit this facility with fluorescent and save energy?

For coolers and freezer environments, Optimum Lighting generally recommends a T5HO fixture.

The T5HO fluorescent lamp emits more heat than a T8 lamp, so by enclosing the fixture, we use the heat trapped within the fixture to create a microenvironment that is conducive to optimal lamp performance.

Optimum Lighting will work with each client to design the appropriate fixture for each temperature need. For example, a 0 degree freezer will need a fixture that traps more heat than a 50 degree dock area. For the 50 degree Fahrenheit area, a deep bodied fixture with a downlight design will maintain enough heat to perform, while in a 30 degree area, a lens would need to be added to ensure additional heat retention within the fixture body. In freezer applications (0 degrees and less), a more compact fixture with a fiberglass body is often recommended (versus the traditional 22 gauge steel of our high bay fluorescent fixtures) – as a means to retain additional heat. Often we recommend the addition of an extra lamp, to increase the heat within the fixture and add a safeguard if lumens are lost due to lower temperatures. (Sample installation Before/After photos)


5) When do you recommend T5HO, and when do you recommend T8?

In general, we try to recommend the technology to our clients that will provide them with the most energy savings, while remaining cost effective and meeting any case-specific need they may have. T8 Fluorescent has the advantage of offering a range of ballast factors – from 0.60 to 1.20, while a T5HO Fluorescent is only offered with a 1.0 ballast factor. The range of ballast factors available for T8 allows us to manipulate the light output of T8 fixtures to more exactly meet our requirements. This advantage of T8 over T5HO is the reason T8 are predominately used for T12 retrofits. A 4 lamp 4′ T12 Fluorescent (4/40 EE/Std), for example, draws 160 watts. Each lamp puts out 2880 lumens, and the ballast factor of this system is 0.88. Assuming a 80% efficiency, the total system lumen output would be:

2880 lumens/lamp x 4 lamps x 0.88BF x 0.80 Efficiency = 6083 lumens

If we wanted to replace this system with a simple T5HO relamp/reballast, we would be greatly restricted since a single T5HO lamp emits 4750 mean lumens and the only available ballast factor is 1.0. If you attempted to replace with 1 lamp, you would be under with only 3800 lumens (assumes same efficiency of 80%), while with 2 lamps, you would be over with 7600 lumens. Now if you attempted the same retrofit with a T8 Fluorescent, you could use a 3 lamp Standard ballast factor system and obtain almost the exact lumens needed (2950 lumens/lamp x 3 lamps x 0.87BF x 0.80 Efficiency = 6160 lumens), while reducing the energy draw from 160w to 80w (at 277V).

Also, T8 technology is an older technology and slightly more energy efficient than T5HO, so we try to recommend it whenever possible. A 400w Metal Halide, for example, can be replaced one for one with a 6 lamp T8 High Bay Fluorescent with a high ballast factor(HBF) Instant Start ballast or a 4 lamp T5HO with a 1.0 BF Program Start ballast (lumen comparison). The 6 lamp T8 HBF draws 218 watts and produces 18,727 lumens, while the 4 lamp T5HO draws 234 watts and produces 17,860 lumens. The T8 fixture produces approximately 86 lumens/watt, while the T5HO only produces 76 lumens/watt.

Despite the advantages of the T8 Fluorescent, there are many applications where we recommend the T5HO. We recommend T5HO in reduced temperature environments, due to the greater heat emission of the T5HO fluorescent lamp (See Question 4). We also recommend T5HO in many sensored applications. Optimum Lighting always recommends that sensors be used in conjunction with Program Start ballasts. A program start ballast has a ‘softer’ start than an Instant Start ballast, and will allow for 50,000 to 100,000 ON/OFF cycles (depending on the manufacturer). Instant Start ballast should not be used with sensors as they will rarely provide more than 7,000 to 10,000 ON/OFF cycles, and will often result in premature lamp and/or ballast failure. Both T8 and T5HO program start ballasts are currently available with 100,000 ON/OFF cycles, so the decision of which technology fits each application is more complicated.

If your client is most interested in energy savings, the T8 program start ballast is the better solution. As described above, a 6 lamp T8 HBF or a 4 lamp T5HO will produce adequate light to replace a 400w Metal Halide. A 6 lamp T8 on a 1.15BF Program Start Ballast factor will draw 216w, while the 4 lamp T5HO will draw 234w. By using a T8 fluorescent fixture, you can save an additional 18 watts per fixture location (lumen comparison).

If your client is most interested in overall cost, the T5HO program start ballast is often the better solution. The T8 and the T5HO program start ballasts are almost identical cost-wise, but since the T5HO system is a 4 lamp system, you can house it in a smaller fixture body (G10). This smaller fixture body allows for a more cost effective overall fixture.

We also recommend T5HO for many 347V applications where a sensor is required. T8 347V Program Start ballasts are not currently available with high ballast factors, so in order to replace a 400w Metal Halide (15,210 mean lumens, See Question 1), you would need to use 7 T8 lamps with a standard ballast factor Program Start ballast (2950 lumens x 7 lamps x 0.88BF x 0.91 lumen efficiency =16,537 lumens) and a much wider fixture design. The same replacement could be done with a narrower design, 4 lamp T5HO 347 fixture, which proves to be a much more cost effective recommendation.

Finally, we recommend T5HO for most 480V applications. Universal Technologies is the only ballast manufacturer that currently offers 480V ballasts for T8 applications, while 480V T5HO ballasts are offered by Osram Sylvania, Advance Transformer and Universal Technologies. Due to the wider availability of the T5HO fluorescent, it is a more reliable ballast supply than the Universal T8 480V Fluorescent.


6) How do I know if lamps are included in a fixture quote?

The designation for lamps can be found at the end of a fixture code and is three numbers. The first number represents the Color Rendition Index (CRI) of the lamps you need. For example, an 8 would mean that you need lamps with a CRI from 80 to 89, while a 7 would mean a CRI from 70 to 79. The second and third number represent the desired Kelvin Temperature (41 for example would mean you need a 4100K lamp). A complete fixture code, therefore, would be G10 454 UV 2PS E 850, which would mean you want a CRI from 80-89 and a 5000K lamp.

Fluorescent High Bay Fixture


Fluorescent High Bay Fixture


Fluorescent High Bay Fixture


Fluorescent High Bay Fixture