Pem’s Tech Blog

My previous post on energy savings per light bulb really left me wanting more data on how number of times turning a light on/off affects the operating life of the bulb / lamp.  Maybe the additional energy isn’t much, but what about the wear / stress on the bulb’ and its operating life?  So I found another source of info:
http://www.energysavers.gov/your_home/lighting_daylighting/index.cfm/mytopic=12280

It prefaces that the (exact number of hours that switching lights on and off reduces the total operating life depends on the type of light and how many times it is switched on and off), and gives a generalization for two very common types of lights:

Incandescent lights: 85% to 90% of the energy is turned to heat (not light), and the actual bulb is cheap (relative to the cost of energy), so they should be turned off when not needed – especially if you’re just in another room.

Fluorescent lights: relative to incandescent lights: the lamps cost more, lifetime is reduced more per off/on cycle, and startup time uses more energy.  The energysavers.gov link claims that a good estimate may be to turn it off if you’re leaving the room for more than 15 minutes (this number may be smaller if you have a very low cost of energy).  Apparently this can also vary based on both bulb and the ballast.

In some apartment complexes, they will replace the main common area large fluorescent tube lights (and ballast) for free.  For such a situation, this would mean to use the 23 sec number (from the Discovery Channel MythBusters test in my previous post) (energysavers.gov said 5 sec) rather than the 15 min number.

Here’s another source, US Energy Star:
http://www.energystar.gov/index.cfm?c=cfls.pr_cfls

Maybe it’s really the same source, but in any case, here it also says, for compact fluorescent lamps (CFL’s), to maximize the lifetime savings and effectiveness of your CFLs by keeping them on for 15 minutes or more at a time.

It also mentions that CFL’s should avoid extreme temperatures (hot or cold) since that can reduce lifetime, and being in an enclosed fixture with no airflow might cause it to generate heat and reduce its lifetime.

Pem (Admin) :: 2009/10/29 (Thursday, October 29, 2009) :: Energy, Power, Electricity, Batteries :: No Comments »

I Google’s this and ran into a Discovery Channel MythBusters video:
http://vodpod.com/watch/47235-mythbusters-lightbulb-experiment

I noticed that in this video that they used the Kill A Watt P3 device, which I also use.  They used the Kill A Watt P3 to measure average watts over 1 hour for each bulb in steady state: incandescent at 90 W, compact fluorescent at 10 W, halogen 70 W, metal halide 60 W, LED 1 W, fluorescent tube at 10 W.

Then they used a digital-based computer sampling oscilloscope, to measure the watts during turn-on.  There is a slight increase in watts as the filament warms up, but it’s not very long.  Their estimate/calculation said that you only save electric bill money by leaving the light on (versus turning it off when you leave the room), if the time (between when you turn it off then back on) is: incandescent at 0.36 sec, compact fluorescent at 0.015 sec, halogen at 0.51 sec, metal halide at ??? sec, LED at 1.28 sec, fluorescent tube at 23.3 sec.  (They skipped the number for the metal halide bulb).

Thank God, at the end of the video, they at least mentioned the other obvious cost question – how does startup affect the longevity of the bulbs?  They tested this by putting the light bulbs on a 2 minute timer, to have them turn on/off for 6 weeks.  At the end of the 6 weeks, every one of the light bulbs burned out, except the LED light bulb.  6 weeks * 30 times per hour * 24 hours/day * 7 days per week = 30,240 times.  Which they claim correlates to over 5 years of turning lights on/off in a regular household.  I wish they took it further, and compared it to a 15 min cycle, a 5 min cycle, a 30 second cycle, and a 1 sec cycle.

In summary, this very strongly argues that it’s generally better to turn off a light when you leave the room, at least in terms of energy savings.

However, it also argues that it’s not healthy to repeatedly turn the light on/off, in terms of longevity (lifetime of the bulb) (operating life of the light).  So this really left me wanting more data on how number of times turning a light on/off affects the operating life of the bulb.  Especially if we consider home automation, such as a motion sensor or a remote control or a light timer.

Finally, let’s not forget there may be some other factors.  For example, light use might in some way affect security / safety (like if having all your lights off increases chance of a burglary attempt), or eye health / comfort (if the light is too bright, and it hurts or damages your eyes), or distraction (from bright light).  For example, if you stare at a screen most of the day (like I do), then it might be healthier for your eyes to have background / ambient lights on and your monitor’s brightness down (warning: I didn’t research this in much detail yet).

I recall a story from the original “Home Alone” movie where the burglars decide to rob a house because they know the owners are on vacation because their light turns itself on via a timer at the same time every night.  Anyway, household security is important, but it’s not the focus of this current topic.

Pem (Admin) :: 2009/10/29 (Thursday, October 29, 2009) :: Energy, Power, Electricity, Batteries :: No Comments »

Energy cost for a house/apartment is typically done in KWH, aka kilowatts hours, aka kilowatts * hours.  For example, if we have a 60 watt light bulb on for 1 hour, then that’s 60 KWH; which at 11.5 cents per KWH is $0.0069 per hr.  Or, if we have five 60 watt light bulbs on for 24 hours, then that would be 5 bulbs * 60 watts/bulb * 24 hours * 1/1000 watts/kilowatt = 7.2 KWH, which at 12 cents per KWH would cost 7.2 * $0.12 = $0.864 = 86.4 cents per day, which times 30 days/mo would be $25.92 for the month.  If the light bulbs were only on 8 hours/day, then it would be $25.92 * 8/24 = $8.64/mo, for those 5 light bulbs.

Here’s a real example of an apartment electric utility bill for 1460 KWH used in one month:
6.00 : Customer Charge
17.75 : Energy Charge at $0.0355  per KWH, for the first 500 KWH
75.07 : Energy Charge at $0.0782  per KWH, for everything over 500 KWH, in my case this was 960 KWH
53.33 : Fuel Charge   at $0.03653 per KWH, for 1460 KWH
1.52 : sales tax
Total Charges: $153.67, plus additional fees for solid waste, drainage, and street service (for driving a car), made the total $169.60

Notice that usage is bracketed (similar to federal income tax brackets).  In a house/apartment that used 1460 KWH last month, it’s reasonably safe to assume that a small change in KWH usage is not going to put us below the base 500 KWH.

So the important number here is:
(everything over 500 KWH) + (fuel charge) = (cost per KWH)

For my example, this is:
$0.0782 per KWH + $0.03653 per KWH = $0.11473 per KWH

However, let’s also account for the tiny $1.52 sales tax:
153.67 / (153.67 – 1.52) = 1.00999

So the sales tax must be 1%, or around 1%, which means:
$0.11473 per KWH * 1.01 = $0.1158773 per KWH

Pem (Admin) :: 2009/10/29 (Thursday, October 29, 2009) :: Energy, Power, Electricity, Batteries :: No Comments »

So much in our modern world (including computer, devices, robots, etc) is powered by electricity – as energy generated a variety of ways.  For many, this is a hot topic in technology / hardware, finances, and eco-friendly / environment.

I’ve made this new category to share some useful info / notes on the topic.

Pem (Admin) :: 2009/10/29 (Thursday, October 29, 2009) :: Blogging, Energy, Power, Electricity, Batteries :: No Comments »