As you might have noticed when you go to an evening baseball game, metal halide (MH) lamps do not achieve their full light output immediately after starting. This is why stadiums typically turn them on in advance of nightfall when it’s not quite dark enough to actually require their light. According to the Lighting Research Institute at Rensselaer Polytechnic Institute:
“[Metal halide (MH) lamps] require a period of time-1 to 15 minutes-to reach 90% of their full light output. This period is called the warm-up (or run-up) time. After a lamp has been on for a period of time and then extinguished, it cannot be immediately turned back on. Before the lamp can be turned back on, the arc tube must have a chance to cool down or the lamp will not restart. This period of time is called the restrike time. Restrike times for traditional probe-start MH lamps can take 15 minutes or longer, but restrike times for pulse-start MH lamps are generally much shorter. According to manufacturer’s literature, restrike times for pulse-start MH lamps can be more than twice as fast as for probe-start MH lamps.”
The warm-up period referred to is what you’re used to seeing at a large stadium or recreational fields when their metal halide lamps first get turned on. The bulb has a very dim glow that gradually intensifies as it runs for longer periods of time. The reason for this is in the mechanical construction of the light itself. Metal halide is an arc lamp. It functions similarly to other high intensity discharge (HID) lights like mercury vapor, high pressure sodium, and fluorescent bulbs. Special salts inside the tube (a mixture of mercury and metal halides) are vaporized into plasma during the operation of the bulb. The bulb has to heat up to a tremendous temperature (several thousand degrees celsius) to operate. As the light heats up, the internal salts evaporate and the quality of the light output changes. This takes time to get to full power (thus the warm-up period).
While the metal halide lights are ubiquitous at stadiums across the country, they are getting replaced more and more by LED lighting technology. Metal halide does provide high quality lighting, but there are some definite drawbacks to its use; for instance, the inability to switch the lights back on after they have been turned off. They also consume a large amount of energy, and require a warm-up period. With an LED lighting, these issues are eliminated - and a lot of sports venues are making the switch already.
Completing a retrofit on such a large scale is a big project, but it will pay for itself in a short period of time through reduction in consumption and maintenance costs, as well as rebates that may apply. There are also various ways to finance an LED retrofit (read here to learn more). For those municipalities managing recreational fields, or for organizations that own sporting venues, it’s well worth the time to explore an LED retrofit. While metal halide bulbs might have been the right answer decades ago, the way forward is with LED technology.