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Light bulbs refer primarily to Incandescent lamps that were introduced in the early 1900′s to replace Gas and Carbon Arc lighting. Incandescent “Bulbs” were used to light homes, commercial businesses, industrial businesses and street lamps. Incandescent bulbs became very inexpensive when produced in high quantities but were inefficient in terms of a short life and produced low lumens per watt. They had to be replaced fairly quickly in commercial and industrial applications and it took a lot of lamps to provide sufficient lighting.

Incandescent bulbs were the mainstay of the lighting industry until the need to improve light quality and efficiency was met with the introduction of the more energy efficient Mercury Vapor bulbs, the first High Intensity Discharge (HID) lamp. Mercury Vapor lamps replaced Incandescent bulbs in street lighting, commercial, and industrial applications because of higher lumens per watt (33-65 LPW) and a 24,000 hour rated life, but Incandescent light bulbs remained the primary residential lighting source because of their soft light and high color rendering index (CRI) of 100. Mercury lamps had a CRI of 25-40 which made it difficult to distinguish colors and had a low visual acuity.

Light bulb design has always been driven by the need for higher efficiency but the introduction of High Intensity Discharge Light Bulbs introduced the concept of task lighting; variable color temperatures and high color rendering HID lamps that were not only efficient but could be used in very specific lighting applications. The following Color Temperature and Color Rendering Index chart may be helpful in explaining what these terms actually mean.

Color Temperature is a measure of the color of the light produced by the lamp. The lower the color temperature, the warmer and more yellow or pink the light will appear. The higher the color temperature the more white and blue/white in appearance. Color temperature is measured in degrees Kelvin (K) as referenced below:

6500°K – Noon-day Sunlight 5000°K – Daylight 4200°K – Cool White Fluorescent 4000°K – Standard Clear Metal Halide 3700°K – Standard Coated Metal Halide 3000°K – Early morning Sunlight; Warm White Fluorescent 2700°K – Standard Incandescent 2200°K – High Pressure Sodium 1800°K – Low Pressure Sodium

Color Rendering Index (CRI) is a measurement of how well colors are perceived under a given light source. Sunlight is the standard for CRI and is rated at 100. The lower the CRI, the poorer colors will appear.

100 – Tungsten Halogen and Incandescent 90-85 – Full Spectrum Metal Halide and T8 and T5 Fluorescent 80-75 – Standard T8 and T5 Fluorescent and Daylight Metal Halide 70 – Coated Metal Halide 65 – Standard Metal Halide 40 – Coated Mercury Vapor 22-25 – Clear Mercury Vapor and High Pressure Sodium 0 – Low Pressure Sodium

The introduction of Metal Halide Light Bulbs and fluorescent Light Bulbs combined the art of lighting variations and the science of efficient light sources.

T12 Fluorescent light bulbs replaced Mercury in commercial applications because of the higher efficiency of 3000 lumens per lamp and 68 LPW, longer life and a greater selection of color temperatures. T12 Fluorescent Bulbs are now being replaced by T8 Fluorescent bulbs that feature 3050 lumens per lamp and 95 LPW, and T5 Fluorescent Bulbs that feature 5000 lumens per lamp and 92 LPW. T8 and T5 bulbs are also available in 3000K, 3100K, 3500K, 4100K, 5000K and 6500K color temperatures and 85-90 CRI. T8 and T5 fluorescent linear lamps are used in residential, commercial and industrial applications and 3000°K, 5000°K and 6500°K are also used as indoor light for plant growth applications.

Compact Fluorescent Bulbs (CFL) feature an E26 medium base and will directly replace Incandescent Light Bulbs; a 100W Incandescent Light bulb is replaced with a 27W CFL Light Bulb at a 73W savings. If every residence in the USA replaced all Incandescent Light Bulbs with CFL Light Bulbs we would dramatically reduce our energy consumption. CFL Light bulbs reduce energy costs, have a longer life and are available in 2700, 3100, 3500, 4100, 5100, and 6500 Kelvin temperatures. CFL lamps are also available with a mogul base for commercial and industrial applications.

High Pressure Sodium (HPS) light bulbs were designed to replace mercury Vapor in street lighting and area lighting applications where energy efficiency and higher lumen output was required and they continue to serve those applications. A 400W HPS lamp produces 125 LPW versus 68 LPW for Mercury Vapor. HPS not only reduced energy costs but a 24,000 hour rated life was equal to Mercury Vapor and as result did not increase normal maintenance costs. 3000°K HPS bulbs are also used for Horticulture flowering and fruiting lighting applications.

Standard Metal Halide Light Bulbs were the direct replacement for Mercury Vapor Light Bulbs and HPS light bulbs in commercial, industrial and sports lighting applications where white light was required.. A standard 400W Metal Halide Bulb produces 90 LPW compared to 68 LPW for Mercury Vapor. A higher color temperature and CRI also increased the visual acuity of each application making it easier to see and read under Metal Halide lighting. The resulting higher lumens reduced the number of fixtures previously used in a Mercury Vapor application and saved energy. One 400W Metal Halide bulb will replace the light output of 40 lineal feet of T12 fluorescent lamps. Metal Halide bulbs are the “White Light” lighting source.

By Brooks Weisblat

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