Theoreretical info does not always prove out in reality. Over simplification is nearly equal to over stupification. Read up on simple things like respiration. C3 plants must photorespire C4 need not. A C3 plants does nearly all its respiration in the dark as a matter of need not choice. The last sentence is even more ludicrous as it is equivalent to saying your bodies blood sugar levels will not flucuate as much over a one week basis if you do not eat over the entire week versus eatting. Besides a bulbs degradation of light quality and quantity is the typical reason to change bulbs, not the wire/element life span.
This is not "theoretical" i Have written this statement based off the factual plant studies that have taken place in "REAL LIFE" and speaking with numerous seasoned and pro growers with experience and all the info i have stated can be backed up if you look further into it and check out how a Class C3 plants function. Let me address the light issue first: Every time you turn on the light the starter kicks in and the more you turn on the light the
more the starter is having to be worked out and the most common reason for HID light failure is the ballast starter dying therefor the less you turn on your ballast the longer your starter will last and you may say "well the heat becomes an issue when left on for a long time" well most people have some sort of exhaust system for their light to expel excess heat and if you don't then you shouldn't have a HID light on in the first place.
And now to answer your "
Respiration" issues: I found this study on respiration done in a study at the U of Colorado at boulder and here is the link as well if you would like to check it out
http://www.colorado.edu/eeb/courses/1230jbasey/abstracts/1.htm : "
while cellular respiration predominates in the dark (although it is a continual process). meaning respiration occurs "during the light hours as well as during the dark hours.
I have also found the following to useful in my study-
"It's been established for many many many years now that cannabis is a C3 plant. It does not need a dark period.
C3 plants gather CO2 only during the light period when they are photosynthesizing. As long as the light is on, C3 plants gather and use CO2 for photosynthesis.
Some growers practice a version of anthropomorphism with their plants. They believe that since people need rest, plants do as well. Concerning cannabis, this is not true.
Every grower can make a personal choice about light cycle. They can save on their electric bill or prolong ballast/bulb life. 18/6 can be less of a "shock" when changing over to 12/12 for flowering than 24/0 or heat issues can be addressed by fewer hours of light, but basic botany has proven long ago that cannabis needs no dark period.
Ed Rosenthal, Mel Frank and Robert Clarke all have covered this extensively over their careers.
www.mellowgold.com/grow/mjbotany-removed/marijuanabotany1.html Marijuana Botany Chapter 1 - Sinsemilla Life Cycle of Cannabis
/www.cannabisculture.com/articles/3127.html Need the dark
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"This is a direct quote from Ed Rosenthal whom most of you know is a marijuana growing guru:
Marijuana plants photosynthesize as long as they receive light as well as water, air, nutrients and suitable temperature. Photosynthesis is the process in which plants use the energy from light (primarily in the blue and red spectrum's) to combine carbon dioxide (CO2) from the air and water (H2O) to make sugar while releasing oxygen to the air.
Plants use sugars continuously to fuel metabolic processes (living) as well as for tissue building. The plant combines nitrogen (N) with the sugar to make amino acids, the building blocks of proteins. They are the substance of plant tissue. When the light is off, the plant's metabolic processes, respiration and growth, continue.
The plant can photosynthesize continuously so it produces the most energy and growth when the light is on, continuously. Continuous light does not stress the plant, which reacts somewhat mechanistically to it.
Plants under an 18-6 light-dark regimen are producing sugar only three quarters of the time. They are thus growing at only 75% of their potential. Leaving the light on continuously will result in bigger plants, faster, which leads to higher yields."
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"The following information is straight from Greg Green's "The Cannabis Grow Bible"
Cannabis is a light demanding plant. Professional growers keep the light on their plants using the 24/0 photoperiod for this reason. Plants that grow under 24/0 flourish and do not need a quantity of darkness in order to rest and perform photosynthesis properly. Plants that are grown in optimal conditions under 24/0 light regime grow vigorusly and the benefits of a 24/0 photoperiod can be seen actively in the results. More nodes are formed, more branches are created, leaf numbers increase, the plant is growing at its finest.
Some growers opt to use 18/6 as their photoperiod. This is 18 hours of light, six hours of darkness light regime. Under these conditions the plant will grow quite naturally but not as vigorously as the 24/0 photoperiod.
The 18/6 photoperiod expels 3/4 the amount of light that a 24/0 photoperiod does. Although this does not mean that a plant produces 1/4 less leaves,branches and nodes under the 18/6 photoperiod, it certainly does show the correlation between light and cannabis growth. As we have said already, cannabis is a light demanding plant. There are no problems associated with 24/0 and although some have attributed cannabis sexual dysfunction (the hermaphrodite conditon) to 18/6 photoperiod these problems are actually the result of heat stress.
A 24/0 photoperiod requires that your grow room temperature be kept well monitored. The 18/6 option is cheaper to run. You use a quarter less electricity and this will have an impact on your electricity bill. Also the 18/6 photoperiod will generally extend the bulb's lifespan. During the 6 hours of darkness the grow room is allowed to cool down for this period but a well maintained good grow room setup should not require a cooling down period.
24/0 and 18/6 both share the same problem though. Once you start the photoperiod you should keep that way especially when the plants near maturity (the preflowering stage). An irregular photoperiod can cause more males than females to develop. It can also cause sexual dysfunction to appear. Whether you choose 24/0 or 18/6 as your vegetative photoperiod try to keep that photoperiod unitl your plants are mature enough to express their sex."
"Most green plants are classified as either C3 or C4 which represents how carbon(C) is used during photosynthesis. 
leaf:cannabis/veggies) gather CO2 only during the light period when they are photosynthesizing. During the dark period these plants only use oxygen for their metabolic life processes. They don't uptake CO2, nor do they use it. As soon and as long as the light is on, C3 plants gather and use CO2 for photosynthesis.