Comparing

Guide to Common HID Retrofits

High Intensity discharge fixtures were the fixtures of choice for most industrial and commercial applications for more than three decades. Advances made in fluorescent lamps, ballasts and fixture design combined with rising energy costs have now made fluorescent fixtures the obvious choice for many of those applications.

HID fixtures fall into three categories; mercury vapor, metal halide and high and low pressure sodium. By far the most common of these (for indoor applications) is metal halide. Despite the obvious advantages of modern fluorescent alternatives, many contractors, architects, and engineers continue to specify and install HID fixtures in new construction. This fact along with 30 plus years of HID usage has created an opportunity of unprecedented proportions for lighting retrofitters.

The Achilles heel of HID lighting is lumen maintenance. Among the advantages of HID to fluorescent retrofits are; better mean fixture lumens/watts, instant on/instant re-strike, improved color rendering and improved color temperature both of which combine to give fluorescents a higher scotopic value, reduced maintenance costs, reduced air conditioning costs, no fire danger, no stroboscopic effect, reduced UV emissions, reduced glare, an increased ability to direct the light where it is needed and a 45-65% reduction in energy usage and cost.

While all of these can be significant in specific applications, lumen maintenance will be a factor in almost all applications. A complete understanding of HID lumen depreciation is therefore essential.

The amount of light produced by an HID lamp (measured in lumens) decreases dramatically with the age of the lamp. Standard probe start metal halides on average lose over 55% of their lumens by the time they reach their "rated lamp life". It is important to understand that "rated lamp life" is defined as the point where 50% of any group of lamps will still be burning. When a group of metal halides reaches the end of "rated life," (20,000 hours for 400 watt, less for larger and smaller wattages) 50% of the original lamps will still be burning and still be depreciating. It is not uncommon to see metal halide lamps still burning with only 15-25% of original lumens.

The newer pulse start lamps are more consistent and on average will retain their lumens better than probe start lamps. Pulse start lamps will retain around 57% of their lumens at end of lamp life.

It is also important to know that, no matter how dim a metal halide or pulse metal halide lamp gets, it will still use the same amount of electricity. Metal halide is by ar the most widely used HID lamp for indoor applications, with its poor lumen maintenance record you might wonder why they are so widely used.

• First, when metal halide lamps came on the market, they were the best alternative available.
• Second, many lighting contractors have continued to install lower cost HID fixtures in new construction because architects, specifiers, and end users have either not been aware of the long term cost of metal halide fixtures or simply did not care.
• Thirdly, metal halide manufactures have published misleading information on their lamps performance. HID manufactures refer to "lumen maintenance" as the light output at "mean" lamp life. You would think that "mean" lamp life would be 50% of lamp life but in lamp manufacturers parlance it is actually 40% of lamp life.

HID manufactures have liberally used the term "up to" to describe HID lumen maintenance characteristics. These semantics lead customers to believe they were getting significantly higher lumen maintenance than they could realistically expect. If a facility owner asked for 50 foot-candles of light on the work plane, at best he might get close to it for the first 8,000 hours of operation after which time his facility was perpetually under lit with occasional bright spots where replacement lamps were inserted and dark spots where lamps were past their "mean" lamp life. Since lumen depreciation is gradual, facility owners usually don't notice lamp depreciation until long after their lighting contractor has gone.

Most fluorescent replacements for HID fixtures maintain 93% or more of their lumens for rated lamp life (not just "mean" lamp life), and on the average will use only 50% of the watts used by existing HID fixtures.

High pressure sodium lamps have better lumen maintenance and efficacy than metal halides but their trademark yellow/orange light has a color rendering index (which measures color accuracy on a scale of 1-100) of just 22 (compared to fluorescents of 83-86) and produce light with a color temperature (measuring where on the visible light spectrum the light from the fixture is located) of only 2100K. These two factors produce light with a scotopic value that is less than 1/3 of the scotopic value of a 5000K fluorescent lamp. This means that you need more than three times the HPS footcandles to equal the brightness impressions of modern fluorescents (e.g. 100 footcandles of high pressure sodium light would be equivalent to 32 footcandles of 5000K fluorescent light). North American Energy Group has more HID replacement fixtures than can be listed here. For information or a list of HID replacement alternatives you should consult with us. HID fixtures come in a variety of efficiencies, so replacement fixture results will vary.