Wednesday, February 24, 2010

Light Bulbs and Exercise

Light Bulbs

Ordinary Household incandescent bulbs or tungsten bulbs convert the energy or electricity into visible light. This is done by heating a filament until it glows white hot. The filament is small, and placed within a glass bulb that in the past was often evacuated of air giving it a tendency to “pop” when broken. Commonly today these bulbs are filled with argon which protects the filament which radiates at over 1800F from touch or reacting with Oxygen found in the air.

How bright a bulb appears is dependent on the amount of power it uses, or how much power it converts to heat. The number of watts that the bulb uses reflects how much power it uses. Although the number of watts is proportionate to how bright an incandescent bulb will shine it is not a measurement of brightness but of power use. This can be seen when one compares the amount of light a 13 watt fluorescent bulb radiates and discovers its is equivalent to the brightness of a 60 watt incandescent bulb. The reason for this discrepancy in power usage is that the incandescent bulb is far less efficient then a fluorescent bulb and converts considerably more energy into heat that is wasted and not used for light.


Interesting statistic.

One Square Kilometer of Sunlight on the ground has about 1 Gigawatt of power. If one remembers from previous blogs 1 Gigawatt is approximately equivalent to an average nuclear power plant, and often times an average nuclear power plant takes up a footprint of over one square kilometer. So why not huge solar arrays? Simply the technology is not there yet. We will address the technology of solar cells in future blogs, but currently due to the difficulty of converting photons or sunlight into usable energy the average solar cell is only 15-20% efficient. That implies if 1 sq/kl of sunlight contains 1 gigawatt of energy, at 20% efficiency it would take 5 times or 5 sq/kl of solar cells to generate 1 gigawatt of energy. The world record for conversion of light to energy by very expensive solar cells known as photovoltaic is just in excess of 40%. Solar cell research is a huge component of space exploration and is rapidly growing in the commercial sector. Great strides are being made in this field and affordable 40%+ solar cells are in the near future.

More fun Energy Facts:

If a 140lb human runs up a 12 foot flight of stairs in 3 seconds they generate about 1 horse power. This does not mean a man produces 1 horse power since a horse can produce this output for a sustained period of time. A typical person can only produce about .14 horsepower in sustained activity; a professional cyclist can produce up to .66hp-.70hp for over an hour.

Energy Weight and Calories

An average Human produces .14 horsepower during sustainable exercises. An average person’s body is about 25% efficient in converting caloric energy into energy output. That said to fuel our body during sustainable exercise uses 4 times .14 horsepower in energy, or .48 horsepower. Sooo…follow me here… one horsepower is 746 watts, 746 watts x .48 = 426 watts = 426 joules per second…x 3600 seconds in an hour = 1,530,000 joules = 367 Calories (check the charts from earlier blogs)..Ride a bike, swim, exercise vigorously for an hour and you will burn around 367 Calories.

Next week: Kinetic energy – let the fun begin.

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