Not all metal halide lamps are create equal.
When they first hit the market, traditional metal halide (MH) lights were considered revolutionary because their high efficiency produced significant energy savings. Pulse start MH lights took the revolution one step further, increasing lamp life and light output through the life of the lamp. But, they used pinched body arc tube designs to generate the light. Formed body arc tubes take the revolution yet another step forward.
Compared to pinched body arc tube lamps, formed body arc tube lamps have improved lamp-to-lamp color consistency, higher lamp efficacy, and faster warm-up. If you use formed body arc tube lamps with pulse start technology, you get all of the benefits mentioned. Let’s see why this is.
Shape = Performance. The part of the lamp that emits the light is the arc tube. In the design of the arc tube, shape is critical to performance. The pinched body arc tube is made from a cylindrical quartz tube with roughly straight walls, while the formed body quartz tube is produced with walls that are curved to follow the profile of the light-producing electric arc. To close the cylindrical tube, manufacturers pinch the ends, which gives the technology its name.
Arc tube geometry is a major factor in controlling thermal characteristics of the lamp. Pinching, or closing the ends of, a large cylindrical tube is very limiting from a lamp design standpoint. But a formed body arc tube allows the lamp designer to optimize the thermal profile of the arc tube to achieve the desired lamp performance characteristics (See Figure).
An MH lamp designer strives to create an arc tube that will heat the metal halides to the highest possible temperature without exceeding the thermal limits of the arc tube materials. Formed body arc tubes with hotter end regions accomplish this better than cylindrical arc tubes do. These formed body arc tubes optimize lamp performance by controlling temperature, which, in turn, increases efficacy and improves color uniformity. The result is a high quantity and quality of light from the lamp.
Benefits of formed body arc tubes. Formed body arc tubes also provide better repeatability of geometry, or lamp-to-lamp performance consistency. In applications where consistency of light output and color are paramount, this kind of lamp gives you a distinct performance edge.
The small end chambers of the formed body arc tube reduce end heat losses and, consequently, increase lamp efficacy. That means a significant energy savings for you—typically 28% over traditional MH technology.
Geometric inconsistencies are reduced even more in the lower wattage (300W and 320W) pulse start lamps recently introduced to the market. This is due to the formed body arc tube’s tipless design. This design is possible because of a manufacturing process that injects the halides and gases through the end of the arc tube, thus eliminating the need for an exhaust tube. The halides distribute evenly along the arc tube wall, resulting in further improvement in color quality.
Cost. With all of the benefits of pulse start MH lamps, especially those that use formed arc tube lamps, why do almost half of new lighting installation systems use traditional MH lamps? Often, the decision-maker chooses to install traditional MH lamps because the initial cost is less than that of a pulse start system. In an owner-tenant relationship, it’s often easier to pass these costs along to the tenant than to invest in further energy savings. However, start up costs can be misleading to owners because while traditional MH systems may be cheaper to install, they actually cost more to maintain than pulse start systems do. When you’re looking at lamp-life and replacement cycles, don’t forget to consider the interruption in operations that relamping may introduce. The energy cost to operate a traditional 400W MH lamp for a year is typically $216. You can achieve the same maintained light level with a 300W formed body pulse start lamp for only $155 per year. Over the 3-year average life of the lamp, that’s a savings of $183 in electricity usage, which is far more than the cost adder of the pulse start system.
One issue in moving to pulse start MH lamps is stocking. If you already stock traditional MH lamps as replacements, you must add another set of items to your database and provide shelf space for them, begging the question, Why are you stocking the older lamps? Make sure your reasons make sense for your operations and your revenue per square foot requirements.
Service contracts offer an advantage for contractors who specify traditional MH lamps. The lower price of the older lamps means the lamp replacement contractor can charge less to do the job, but that results in higher costs of ownership for the end user.
The real benefit of efficient lighting is to the person paying the energy bill. A contractor who has the interests of the customer in mind will provide the facts and let the customer decide whether or not to make the investment in the more advanced technology. If you’re the facility manager, you need to make that decision and review your specifications accordingly.
Harding is the vice president of engineering at Venture Lighting, Cleveland.