Metal Halide Lamp

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It is necessary to have a bright, efficient, long-lived light source with a good Color Rendering Index (CRI) to use for working with photovoltaic  (PV) devices. The lamp becomes the basis for all comparisons between devices and lighting conditions, so it has to be good. We are using a Metal-Halide (MH) lamp as a reference for all our comparisons. MH lamps are not common in the consumer market, so we'll indroduce our reference lamp here. To see how the lamp compares with other sources, see the lights page.

MH lamps require a ballast to function. The match between ballast and bulb must be exact. See the manufacturer's literature to match a bulb with a ballast. The ballast may be solid state or “iron”. We are using an iron core ballast matched specifically to our bulb. The photographs below show the lamp we are using as a test reference. The test stand is made from aluminum extrusion, an old magnifying lamp arm assembly, a custom-made bracket and balance-weight, and a high-voltage (4kV) high-temperature socket made for MH lamps. The ballast runs hot to the touch. This is normal, but unpleasent. We set the ballast on a sheet of aluminum with heat-sink compound to draw away some heat and lower the ballast's running temperature. The aluminum sheet gets noticably warm. The sign on the lamp fixture reminds the operator to not move the lamp fixture while it is in operation, since this will damage the bulb and ruin its calibration.



Specifications on the bulb include:

  1. Philips MH175/RFL

  2. 175 watts

  3. 55 degree beam (flood)

  4. M57/E ballast required (we used

    a Sylvania M175/SUPER5-kit)

  5. 3700K color temperature

  6. 55 CRI

  7. 10,000 initial lumens

The PV modules were evaluated using this lamp. It is a Metal Halide (MH) lamp which belongs to the High Intensity Discharge (HID) class of light sources. MH lamps provide intense beams of good Color Rendering Index (CRI) and color temperature. The amout of heat in the light stream is surprising low, considering its brightness. This allows testing PV modules under simulated daylight conditions without overheating the silicon.

MH lamps are found mostly in commercial and industrial applications. They are expensive ($88 for the ballast and $85 for the bulb, $5 for the socket), but are efficient and have a long operating life. MH lamps excel in high-power applications such as warehouse and stadium lighting. The color temperature tends to be a bit cool in the more efficient lamps, but is usually not remarkable. MH lamps have a number of requirements and some rather serious saftey precautions that should be understood before application. See the manufacturer's literature before working with MH lamps. MH lamps should “burn in” for 100 hours for their output to stableize to a reproducable value.