Electric light bulb

New light bulbs – CFLs (Compact Florescent Lamp) and LEDs (Light Emitting Diode), use much less electricity. Watts were a good way to measure electrical load but not a good way to measure light output. Better units are “lumens” and “color temperature”.

Lumens are a measure of light output as the human eye perceives the brightness and has nothing to do with the source or efficiency. Since we have been measuring light output over a hundred years by wattage, we are all familiar with the light output of various wattages. Compare lumens to the old wattage standards. The actual wattage of the new bulbs will be much lower, so higher efficiency and savings.

Incandescent watts lumens new bulb actual wattage
25 250 4/9
40 450 9/13
60 800 13/15
75 1,110 18/25
100 1,600 23/30
125 2,000 23/40
150 2,600 40/45

From the chart above, the 100 watt incandescent light bulb puts out about 1,600 lumens. The new CFL (compact fluorescent light) will put out the same amount of light (lumens) but only draws 23 to 30 watts of power. The new LED (light emitting diode) will be even more efficient producing the same lumens with even less wattage.

At some point in the future when there are no more incandescent bulbs being sold, the wattage comparison will be removed from the packaging. The information needed to get the correct bulb will be lumens, color temperature, and if the bulb can be dimmed.

LEDs – reducing the world’s energy consumption, some 25 percent of which now goes to lighting, while illuminating remote villages with solar-powered LEDs.

power consumption of light bulbs

Energy Star is a joint program of the Environmental Protection Agency and the US Department of Energy to help consumers pick the most energy efficient products on the market. Any device that consumes electricity and bears the “Energy Star” label has been tested and has a ranking so the consumer can make a choice that will save that consumer money. Results are already adding up. Americans with the help of Energy Star in 2010 alone were able to avoid greenhouse gas emissions equivalent to 33 million cars while saving 18 billion dollars on energy bills. Light bulbs are a big part of that program. Look for the “Energy Star” label on the packaging for maximum savings. –Les Lowman Apr2012

Color Temperature – The old incandescent light bulbs had no choice of color – warm color. The new CFLs (compact fluorescent lamps) and LED (light emitting diode) bulbs when first introduced had a very white light that was good for seeing but a little stark and cold for aesthetics.

As the new bulbs became more popular consumers were looking for light bulbs that would work in various places like bathrooms and kitchens. They didn’t want that cold stark white that was good for the work shop or high light tasks. Manufactures put in much research to find ways to provide a range of colors. There is a number for that – called “color temperature”.

Color – In pigments (paint) the primary colors are red, blue and yellow. White is a lack any color and black is all the primary colors at once. In light, the primary colors are red, blue and green. Black is the absence of light and white is the combination of all three, just the opposite of pigments.

Sunlight contains large amounts of all the primary colors which gives very white light and has a color temperature of about 5500K (Kelvin). A candle has a color temperature of about 1900K. This color only, not brightness.

Color temperatures as relevant to lighting – Because the old incandescent light bulbs make light by making a filament hot, the first color to come off is red. As the tungsten filament gets hotter it goes to orange, then almost white but not quite. Flash bulbs make white light but not for long. The color then is a compromise between color and longevity of the filament. This is the design voltage of the filament. A higher voltage on the filament would give whiter (higher color temperature) light but shorter filament life. An old trick in industry was to use 130 volt bulbs in standard 120 volt circuits and get longer life (less replacements) at a cost of lower light and more yellow or lower color temperature.

CFLs ionize a gas in a glass tube. The inside of the tube is coated with special powders that “fluoresce” in the presence of the ionized gas. Major strides have been made in recent years to not only make these powders more efficient but also control color temperature. The same has happened with LEDs. The method of controlling color temperature is very complex, suffice to know it can be done.

When buying light bulbs, select a bulb that will give the amount of light or brightness (lumens) and select a color temperature that is suited for the lighted area. Color temperatures start at about 2700K which are considered “soft” and go well in areas where skin tones are a concern. They go up to 5000K which is very white for fine work such as sewing or a work shop but are not suitable in a bathroom.

Because these numbers are new to consumers, most stores have displays that show various bulbs and respective colors in little miniature house rooms. Get used to “lumens” (brightness) and “color temperature (warm/harsh) rather than “watts” when it comes to lighting.

A kilowatt hour is 1000 watts for one hour. That’s the way the electric company bills consumers. In the near future, most of the electric bill will be for heat/air-conditioning, hot water and appliances that make heat. Very little of it will be for lighting. –Les Lowman May2012

That’s engineering

  • greenhouse effect – the warming of the Earth’s surface by solar radiation trapped by a build-up of carbon dioxide and other atmospheric gases.
  • Fluorescence – This type of glow occurs when some form of radiation, such as light, causes an object to glow. For example, fluorescent papers and poster boards glow in the daylight. They may seem to glow even brighter under black light (ultraviolet), but in either case, as soon as the light is removed, the glow stops. Fluorescent things do not glow in the dark all by themselves – they require some other form of energy such as ultraviolet light to “excite” them.
  • Phosphorescence – Phosphorescence is just like fluorescence, except that the glow continues even after the light used to excite it is removed. “Glow in the dark” toys phosphoresce brightly in total darkness after being “charged” or excited by ordinary white or ultraviolet light.

Engineering ideas

  • lumens, watts, LED, CFL, energy efficiency, greenhouse gas, emissions, ionization, fluoresce, brightness, color temperature,

Do It
Challenges for you to work on…

  • Black light secret message – With the Black Light Secret Message experiment, you’ll see that certain highlighters aren’t just brightly-colored – they’re actually fluorescent and glow underneath a black light.

Learn more…

  • Energy Star
  • Environmental Protection Agency
  • US Department of Energy