Whenever possible, the lamp numbers used in this catalog are the industry standards as recorded with the American National Standards Institute (ANSI). Many lamps listed in this catalog are new or special lamps which carry PICC identification numbers.

This column in our catalog lists the voltage at which the lamp is designed for best overall performance considering amperes, candlepower, and life.

The power consumption (watts) or current rating (amps) at the design voltage is listed in this column of our catalog. All Amperage ratings are to be considered +/- 10% unless otherwise specified. For the application, it should be considered that the initial current applied to a cold filament can be 10 to 12 times greater than the lamps rated current.

This value indicates the total light output of the lamp at the design voltage when measured in an intergrating sphere. The M.S.C.P. can be converted to Lumens by multiplying 12.57 by the M.S.C.P.

Rated design life is the average life in hours obtained under controlled laboratory conditions using 60 hertz AC designed voltage. Service conditions such as shock, vibration, temperature, constant current operation, and DC voltage contribute to shorter average life.

Filaments listed in this catalog are identified below:

Since incandescent lamps may be rerated to suit various design goals, existing standard lamps should be reviewed prior to initiation of a new lamp design. Three basic formulas apply when rerating a lamp, assuming that VA equals application voltage and VD equals design voltage, the following may be applied:

The chart illustrates the correlation between voltage, current, candlepower, and may be used as a guide in the application of vacuum type lamps.

The following is an example of the charts use. A 5 volt lamp operated at 6V (120% of the design voltage) yields the following characteristics:

MSCP=1.893 x 5 v MSCP rating
Life=0.112 x 5 v life rating
Current= 1.105 x 5 v current rating

Note: Calculations of characteristics for lamps operated at more than ±10% of rated volts will result in values which may vary widely from the actual results.

The initial current applied to a cold filament can be 10 to 12 times greater than the lamps rated current. As resistance causes the filament temperature to rise, the inrush current decreases. The steady state value of current is reached when the thermal energy output is equal to the electrical energy input. Inrush current can be reduced by using a low voltage to preheat the filament, and is important when lamps are used in a flashing or pulsing display.

Subminiature vacuum lamps can be used in flashing or pulsating applications without reduction in life so long as the pulsing or flashing mode does not exceed that of the steady state operating specifications.

By varying the filament wire diameter, coil size, and spacing, as well as voltage and current, the rise time of a miniature lamp may be varied from 20 to 200 milliseconds from cold operating temperature.

The rise time of a given lamp may be accelerated by the use of a waveform with a high voltage front, phased in time to reduce it to the design voltage level when the filament reaches the design temperature.

With equivalent RMS values, a tungsten filament lamp will operate equally well with AC or DC voltage.

When the power source is optional and a long, uninterrupted service life is required, AC operation is preferable. The notching effect experienced with DC operation can cause reduction in life of 50% or more. During its normal operating life as an incandescent element, the tungsten filament steadily boils off tungsten atoms at a rate strongly dependent upon the temperature. Non-uniformity of filament material or cross-sectional area, traces of lower melting point materials, mechanical effects of cold working, and similar influences produce anomalies that cause preferential evaporation. Notches are formed at tiny hot spots in the filament, until eventually a shock causes the filament to snap at the weakest notch. Since the size of the notches seems to be independent of the size of the filament, thinner filaments show a more reduced life compared to the larger, higher current rated filaments.

Design voltage will determine the filament length and diameter. In most cases, the higher the voltage, the longer and thinner the filament is. Amperage is determined by wire diameter and operating temperature. Higher voltage lamps present mechanical packaging problems and tend to be more susceptable to mechanical shock and vibration than the lower voltage lamps. In general, shorter filaments with current ratings in excess of 50 milliamps and voltage up to 7 are the least susceptable to mechanical breakage. Unlit filaments are more resistant to shock and vibration because the unenergized tungsten has approximately ten times the tensile strength of its energized counter-part in the early part of life. However, in an older filament, the notching effect negates the aformentioned and a maintaining current should be used to increase the filament ductility and off-set the unlit brittleness.

The Glass used to manufacture most envelopes (bulbs) will begin to outgas when its surface temperature rises above 104°C. Outgassing accelerates as the surface temperature rises and be 132°C, lamp reliability is severely decreased. Usable life is drastically shortened due in great part to the initiation of the so called "water-cycle" described below.

Water vapor, caused by outgassing, is disassociated by the hot filament into hydrogen and oxygen. Oxygen reacts with the hot tungsten to form tungsten oxide which is evaporated and deposited on the interior bulb surface. Meanwhile, the highly reductive hydrogen migrates to the deposited tungsten oxide, reduces it, leaves the deposit as ceombined water vapor and begins its cycle all over again.

Home | What's New | Products |Quality

Request Catalog | Company Information

Send mail to webmaster@harison.com with questions or comments about this web site.
Copyright © 1999 Harison USA
Last modified: May 13, 1999