I have installed T-5 fixtures (5 -4ft bulbs per fixture) in place of 400 watt metal halide high bay fixtures with great results. The lighting is slightly brighter, and seems to be of much better quality.
I have not made any measurements, but I can't imagine the electronics for the fluorescents to be any worse than the electronics used by the HID ballasts.
#175763 - 03/10/0809:36 PMRe: Replacing metal halide high bays with fluorescent
I've replaced several 400W MH fixtures with 6 lamp T5's in several different businesses. Each installation to T5's improved the light (more) and resulted in less electricity (aprox 1/3 less) usage. No one has complained of any harmonics or causes any electrical problems with other adjacent tennats. Defineatly the way to go, especially if your changing out ballasts on the MH fixtures, plus you have advantage of instant on. Our price was about $215 per fixture plus 6 blubs at 6.50 each. Highly recommended.
Ballasts=feedback harmonics. Not sure the dif between the two types on your application. They have meters to measure such things, but they are around $2K. Might be able to rent one if you're lucky though. Good luck!
#175826 - 03/12/0807:39 AMRe: Replacing metal halide high bays with fluorescent
Change them ASAP. The lastest and greatest fixtures do not present Harmonic problems. Light output will be much better. Also each individual fixture can be ordered with a PID sensor for even better savings.
#175828 - 03/12/0809:34 AMRe: Replacing metal halide high bays with fluorescent
We use a lot of the Highbay 4, 6 and 8 Lamp T5HO Fluorescent Fixtures - with Reflectors and Parabolic Diffusers.
They are a much better choice for wide spread area lighting than an HID Highbay or Lowbay, as the linear Lamps have a good light spread - especially with the reflectors and Parabolic Diffusers!
The THD (Harmonics) of the Electronic Ballasts does not result in anymore L-N Load Current then what is produced by a typical CWA Reactor based HID Ballast. Maybe an additional 5% if the Circuits are loaded to Maximum, and the Ballasts are "Noisy" (>20% THD).
The typical tradeoff for a Lighting Retrofit (old Probe Start Metal Halide fixtures replaced with T5 HO Fluorescents) is a drammatic reduction in drawn Kilowatt Hours, while still retaining the same level of Light (and a much "cleaner" light output too!). Clients receive conservation + reduction benefits, and typically the retrofit pays for it's self within 2 years.
The Ballasts driving the Lamps on the fixtures I typically Specify / Design with, are "Programmed Start" instead of just plain old "Instant Start". The Lamps are started in the "Hot Cathode" mode, and as they are run, the Cathode Heating is reduced accordingly. This results in excellent Lamp efficiency + effecacy (read: high, stable light output), best life operation, and since the Cathodes' heat is reduced during operation, the total drawn wattage is reduced at that time
Standard "Rapid Start" methods are great for Lamp operation, but power is wasted by continuously heating the Cathodes at the same level.
"Instant Start" methods use "Cold Cathode" operation, but the Lamps are not running at their optimum output. The Cathodes are not heated, so there is no "Parasitic Load", or "wasted power" to heat the Cathodes; the tradeoff is lower power drawn through the Lamps, and results are lower Light output.
Scott " 35 " Thompson Just Say NO To Green Eggs And Ham!
#175871 - 03/13/0810:54 AMRe: Replacing metal halide high bays with fluorescent
Scott made mention of T-5's having a 'cleaner' light. I know, that's not an easily defined term ... but it's still true, regardless.
Comparing 400 watt MH to 5-tube T-5's, in actual use the overall level of lighting seemed identical. That is, the side of the shop with the T-5's did not seem any brighter than the side next to it, with the MH. Yet ... on the T-5 side ... the light seemed 'softer,' colors clearer, shadows lesser. You just seemed to be able to see things better - especially when doing detail work on a bench.
The power savings are very real, as well. The same light, or better, for about 1/3 of the electric bill. Other advantages were a lesser load on the air conditioning (HID gets HOT!), and the fact that the fixture never goes completely dark. That's what happens when the only bulb or ballast in a fixture goes bad; the T-5's I saw had 5 bulbs and 2 ballasts.
The term "Cleaner Light" is just my interpretation - not any justifiable term. The Light output appears more uniform and less distorted. This must be contributed by the 20kHz Lamp operating Frequency, the Parabolic Diffusing apparatus, the use of "HO" (High Output) Lamps, and the 5,000K Color Temperature Lamps.
The power savings is the most apparent thing between the two technologies. Along with this, there are other benefits such as what Reno mentioned - Lamp failure does not take out an entire fixture, only one or two Lamps of an array will be affected.
Additionally, the total heat produced is somewhat less with Fluorescents, and the Fluorescents have an "almost instant On" characteristic, one which is not in comparison with HIDs - even PSMH Electronic Ballastry - Auto Dimming.
The usage of Linear Fluorescent Bay Fixtures -vs- an HID Bay Fixture depends mainly on the Environment, as follows:
*A An HID Fixture may be better suited where tasks are in specific points - so the light is concentrated more in the task area, rather than a wide distribution.
*B An HO Linear Fluorescent Fixture may be better suited in Warehouses (like Racking Aisles), because a wide distribution of light is needed overall, instead of specific point intensities.
Scott " 35 " Thompson Just Say NO To Green Eggs And Ham!
#175979 - 03/17/0803:17 AMRe: Replacing metal halide high bays with fluoresc
Good stuff guys!, I am also a big fan of the newer T-5 fluorescent fittings. I've used them in quite a few applications, including factories, the "yards" of a slaughter-house, they even make a street-light-type fitting that uses these lamps.
The only down side to these fittings that I have experienced, is temperature changes can cause the light output of the tubes to vary slightly, but it is not a big variation.
I would be interested to see how a M-H lamp actually stacks up against a T-5 fitting, using real-world analysis, not the information given in lighting company literature, where the tests are often done in some sort of a laboratory. I believe the first place to start would be comparing the output of the two lamps in lumens/watt. Any takers?