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on January 19, 2016

Pulse Start vs. Probe Start Metal Halide Lamps: What's The Difference?

You may have heard the terminology "pulse start" and "probe start" in relation to metal halide light bulbs, but what does that even mean? And when you're faced with that epic dilemma: “Which metal halide lamp do I choose?” and you're not a certified lighting professional, what's a person to do?

Gather round, young grasshoppers, let me explain.

Probe Start Lamps

These are the traditional metal halide lamps. They're characterized by their 3 electrodes in the arc tube (1 starting probe electrode, and 2 operating electrodes). To start, a discharge is created across a tiny gap between the starting probe electrode and one of the operating electrodes, electrons leap across the arc tube to the other operating electrode. Thus, the lamp "probe starts," and a bimetal switch removes the starting probe electrode from the circuit.

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Pulse Start Lamps

Consider the pulse start lamp the probe start's hip younger brother. These lamps don't have a starting probe electrode, but instead have a high-voltage ignitor that works along with the ballast to start the lamp using high voltage...you guessed it...pulses!

Check out this diagram comparing the two lamps (from LRC.RPI.edu):

Pulse start innovations

A wee bit of trouble: The probe starting method reduces the lamp's performance over time, because with each start, tungsten sputters from those frisky electrons, blackening the tube. Therefore, several states have phased out certain probe start metal halides.

The pulse start has made many improvements to the metal halide lamp, even allowing the Department of Energy's efficiency standards to rise:

  • Without the probe electrode, there's less sputtering, hence less blackening, hence a longer lamp life. It has improved lumen maintenance by up to 33%.
  • Because this lamp is sans probe electrode, it doesn't need as much pinch (seal) at the end of the arc, reducing heat loss.
  • The lamp has a faster starting and re-strike time, and can start at temperatures as low as -40 degrees Celsius.
  • With a long lamp life of up to 26,000 hours, these light bulbs can even rival LEDs for efficiency!
  • When replacing probe starts on a one-for-one basis, pulse starts can save up to 20% of energy used (remember: most pulse starts require compatible pulse start ballasts).
  • The higher light output of a pulse start lamp allows fewer lights for the same amount of lumens.

Plus, there are a couple of new innovations that make pulse start metal halide light bulbs even more user-friendly:

  • Miniaturization: Pulse starts now come in wattages as low as 15W (which could replace a 12-volt 50W MR16 light bulb, and save up to 32 watts per light bulb!)
  • Rendering of Red: New pulse start technology has improved the way the lamp portrays the color red. This makes it more applicable in retail displays.