However, making bulbs smaller isn't a simple process; designers have to consider many aspects of thermal control when altering the size and shape of the bulb and arc tube inside a bulb.
Size and shape help control the life of the bulb: if a bulb is too small, it can drive up the voltage of the lamp, which is a condition that leads to end of life. EYE Lighting, an Ohio-based manufacturer of lamps, luminaries, and lighting products, has recently added a new shape to their line of Cera Arc Ceramic Metal Halide products. The EYE Cera Arc ED23.5 Mogul Base lamps have the same power as versions with a larger diameter, but are designed to replace up to 250 W pulse start metal halide systems in outdoor (street, landscape, parking lot, and security) or indoor (industrial and warehouse) applications.
The smaller diameter of this lamp gives fixture designers more freedom in their designs with the same light output and energy efficiency. This family of lamps also provides better color and temperature performance, a longer life, and better lumen maintenance than competitor projects, explains Peter R. Ness, manager of technology, quality, and product development for EYE Lighting.
Ceramic Metal Halide Arc Tube The Cera Arc family of lamps are made with a ceramic metal halide, which allows for higher performance, offering both higher temperatures and longer life more efficiently than other materials.
The Cera Arc Ceramic Metal Halide lamps are categorized as High Intensity Discharge (HID) lamps. These lamps may be driven by electronic ballasts as well as more traditional core and coil ballasts. Electronic ballast sighting bolt between two electrodes when these lamps operate," he continues. "From a design point of view, the size and shape of the arc tube has a lot of considerations for thermal management."
The Bulb "From a design point of view, the melting properties of the glass are very important," says Ness.
The bulb in this lamp is made of borosilicate glass, the same material that Pyrex dishes are made of, and the same material used on the space shuttle. Borosilicate glass can go from a very low to a very high temperature quickly without breaking because it has a high coefficient of thermal expansion and good thermal shock resistance, but can also be melted during the production process. Bulb size and shape also impact the life of the lamp, says Ness. "If your bulb is too small, you can actually affect the operating voltage of the arc tube. If you make the arc tube operate at too high of a voltage, you'll have a very short life. It might be really bright, but it won't last too long."
The getter is used to keep the inside of the bulb clean, which helps increase the product lifespan by cleaning "atomic size" contamination that might remain in the bulb after it's put together.
The ED23.5 lamp uses two getters - a strip getter and a barium getter. In this case, the barium is evaporated from the getter (hence the black smudges near the bottom of the bulb) and cleans the lamp.
Wire Frames & Stem
Wire frames hold the arc tube in place and attach to the stem. There is also a small piece of glass in the stem that is melted to connect with the outside bulb during the lamp-making process, a challenge when the two pieces are made from different types of glass that must be hermetically sealed together.
The base is made of a nickel-plated material, which helps create lubricity inside the sockets. Lamps like this one are often used outdoors, where weather can corrode fixtures. Nickel is a non-reactive material that helps the base stay "slippery" overtime.
Ceramic Materials & Eyelet
The lamps use a ceramic material at the bottom of the base as insulation to help the lamps withstand the high starting voltage peaks that electronic ballasts can put up. The eyelet, at the very bottom of the lamp, facilitates the electrical connection.