Energy Audit

Digital photography requires electrical energy at each step of the process. This page presents some results of a real-world energy audit of a working digital photography studio, with a focus on computers and digital storage components. It also presents measurements and suggestions related to lighting and heating.

Measurement method
Factor in your electricity costs
Measured results - computer systems
Measured Results - Components
Wireless thermostat control

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Electricity is an invisible background cost to much of digital photography. While there are some energy components with obvious cost, such as use-once AA batteries, most of the energy costs are lumped into one single catch-all power bill. This bill may also include costs for heating, cooling, hot water, lighting and refrigeration. This can obscure the cost of particular components and practices.

By measuring the energy use of individual systems or components, it’s possible to get a clear picture of the cost of the equipment you use and the way you use it. When you factor in the rate you pay for electricity, you can get a good understanding of the true cost of leaving your computer on overnight and other practices.

While measuring the energy consumption can give you an idea of the energy used, that is not the total picture regarding some energy practices. Any equipment with significant energy consumption probably also generates heat. If you live in a warm climate and use Air Conditioning to any significant degree, there might be additional energy costs that are even harder to measure. (Of course, if you live in a cold climate, this excess heat may be welcomed.)

As part of the audit process, we also looked at other energy consumption. Lighting, in particular, was an area of surprising cost, and one where it was possible to make significant improvements easily. Additionally, we found that heating and cooling costs could also be addressed through the use of wireless-enabled thermostats.

Measurement method

The tests reported on this page were made with a P3 brand Kill A Watt meter, as shown in Figure 1. This inexpensive and easy-to-use device shows you the actual energy consumption of any device you plug into it. It will also keep track of the usage over time, and show you total energy consumption over a specific time period. ´┐╝

(Insert Figure 1 - Kill A Watt meter with computer plugged in_

Figure 1 The Kill A Watt meter is an inexpensive device that can tell you the energy usage of any device you can pug into it.

In this audit, various digital imaging tools were measured, both at rest and at work. The principle goals were to determine what the energy costs were to operate the equipment, and to see if there was any place where it made sense to change how that equipment was used.

A few notes about our methodology:

  • For many of the items measured, it was sufficient to get a snapshot of usage at any given time. These were recorded as the watts.
  • Of particular interest was the energy used when a device was in standby mode, as this is a place with the potential of actionable information. This was also measured in watts.
  • If a device in the studio, such as the file server, is typically running in the background, then the device was measured over a period of several days to provide a real-world assessment of energy usage. These figures were measured in kilowatt hours, which is the unit of measure on your power bill. A kilowatt hour is the equivalent of running a 1000-watt device for one hour.

Factor in your electricity costs

Before measuring, you’ll want to know the cost of your own energy. Most electric bills are less than totally straightforward with this information. There are a host of taxes, fees and other service charges on many power bills. In general, your bill will be divided into two kinds of charges: the cost of providing the connection, and the cost per kilowatt hour.

You may need to look at several bills from different times of the year in order to get a good average cost for your kilowatt hours. The price can fluctuate over time, and the price may also be pegged to a sliding scale where it changes depending on how much is used.

In the Krogh studio, the average cost per kilowatt hour is approximately $0.15. This cost can be used to provide some basic numbers to use in evaluation.

  • A 1000 watt device running full time for an entire year costs ($0.15)x(24hours)x(365days)= $1314
  • A 100 watt device running for a year is 1/10 of that, or $131/year
  • A 10 watt device running for a year costs $13/year
  • A 1 watt device running for a year costs $1.30
  • A 100 watt device running for an eight-hour work day costs $31/year

Make your own table

If you find out your own kilowatt hour costs, you can make the same table. This is a very handy tool when comparing electricity costs.

Measured results - computer systems

Now that we have the methods and costs outlined, here are the results of a number of measurements, along with some comments about how to make use of them. Some of these results are listed as a range. Note that the Kill A Watt meter has an accuracy of plus-or-minus 1 watt, so readings below 3 watts are not particularly accurate.

Mac Pro tower computer

This is an older Quad-core Intel machine. It has four internal hard drives, a 30-inch Apple monitor and a Wacom Cintiq attached. It was measured in three basic states: working hard, awake but not working hard, and asleep. Here are the results:

  • Working hard: up to 500 watts
  • Awake, monitors lit up, hard drives spinning but no significant processor activity: 390 watts
  • Sleeping: 15 watts
  • Power off: 1-5 watts

Conclusions: This is the workhorse of the studio, and it is typically left in sleep mode overnight. As long as the computer actually sleeps overnight, the yearly cost for leaving the computer on is under $10.

iMac file server

I use a 20-inch Intel iMac as my studio’s file server. It is connected to a Drobo four-bay hard drive enclosure, as well as a no-name four-bay hard drive JBOD. This machine is always awake and available over the network. In addition to the computer itself, there are two ventilation fans in the housing the computer lives in. Due to heat build up, these fans are constantly running for about six months a year.

This machine gets use at all hours of the day and night. Not only does it get used to serve up archived files, but it is also the location that all studio computers backup to. Since this happens in the middle of the night every night, this machine must be on all the time.

  • Awake but at rest: 100 watts
  • 65cfm fans (2 @ 20 watts): 40 watts

Conclusions: I was pleased by the low power draw of this unit when at rest. It would be a real inconvenience to have to sleep the unit. I was surprised by the power draw of the cooling fans, and will consider replacing them with lower power versions (especially since these are getting old and sometimes make noise when running). The yearly power cost for keeping this machine running is under $200, factoring in the run-time of the fans.

17-inch MacBook Pro

This is a 2009 Intel Core 2 Duo 2.8GHz machine with a 7200 RPM Seagate 750GB drive. These first measurements were done with a full charge, since that should show power draw exclusive of the power that would be required to charge the battery.

  • Running, low processor draw, backlight at lowest setting: 30 watts
  • With finder calculating folder sizes, one processor at 100%: 50 watts
  • Backlight on highest: add 8 watts
  • Asleep, battery charged: 1 Watt

Conclusions: As you can see, the processor is a significant power draw, and the power draw when sleeping is very low.

Power Mac G4 print server

This computer only exists to run the printers in the studio. It is a much older machine running with three internal hard drives, a 15-inch flat-panel monitor, and a powered USB hub. Typically, this machine is left on and awake, so that it can be seen over a network and is ready to receive any files that are sent to print.

  • Working hard: 170 watts
  • Awake but at rest (monitor sleeping): 140 watts
  • Asleep: 20 watts
  • Power off: 10 watts

Conclusions: This computer costs approximately $200 a year just to maintain a ready state for printing. Since printing happens only once a week or so, it makes sense to sleep this machine when not in use, and wake it up when I need to make a print. This also makes sense because I will always be at the machine whenever I actually make the print, so waking it up prior to file transfer is little additional hardship.

I was surprised that the computer itself drew 6 or 7 watts even when it was turned off, but this is an older model, and energy efficiency standards have definitely increased in recent years. Savings: $180/year

Measured Results - Components


This is the original four-bay USB Drobo unit. It is equipped with 500GB 7200 RPM Hitachi hard drives.

  • Working hard : 45-55 watts
  • Standby mode: 4 watts

WiebeTech four-bay RTX RAID

4 x 500GB 7200 RPM Hitachi drives

  • Working hard: 40 watts
  • Standby: 6 watts

Drives in “toaster”

WD 2TB Green 3.5-inch drive

  • Powered up: 7-9 watts
  • Working hard: 10.8 watts

Seagate 400GB 7200 RPM 3.5-inch drive

  • Powered Up: 12 Watts
  • Working hard: 15-16 watts
  • Seagate 500GB 5400 RPM 2.5-inch drive
  • Powered up: 3.5 watts
  • Working hard: 5 watts


  • D-Link Gigabyte switch: 4.5 watts
  • D-link wireless access point: 4.5 watts

Cable TV converter box (not a DVR):

12 watts

Sony stereo receiver

  • Playing, soft to loud: 30-45 watts
  • Off: 0.4 watts


After measuring the power draw of computer equipment, we turned our attention to lighting. In this case, we were not looking at photographic lighting, but instead at general studio and workspace illumination. We did this because this type of lighting is typically switched on for long periods of time, and because there is more choice for energy efficient alternatives.

Simple math

It’s easier to estimate the power draw of conventional lighting than many other electrical devices. All lighting has a wattage rating, and you can determine power consumption by simple math. Using the table at the top of this page, it costs $31/year for a 100 watt bulb to run each workday for eight hours. If you count up the total wattage of your work-day lighting, you will find the yearly lighting cost.

Replacement bulbs

Once your lighting costs are known, the decision to replace the existing lighting with more energy efficient bulbs is much easier to make. Here are some considerations about lighting types.

  • Incandescent: Incandescent bulbs have been described as space heaters that also happen to give off a little light. They have the advantage of coming in many form factors and being dimmable, and generally producing a good quality of light, but they can be very expensive to run. They also have a relatively short lifespan.
  • Traditional Fluorescent: These long thin bulbs have been the lighting of choice in institutional environments due to the low cost, high output, low heat output and long life. They don’t fit in some environments due to the large form factor.
  • Compact Fluorescent (CFL): These bulbs are roughly four times as efficient as incandescent. A 60 watt incandescent may be replaced by a 15 watt CFL. They don’t come in as many form factors, but that is changing. They are typically not dimmable, and even the ones that do dim don’t do it well. And many people don’t like the quality of light coming from these bulbs.
  • Light Emitting Diode (LED): These are the newest class of task lighting, and improvements are taking place rapidly. They are even more efficient than CFL, with 60 watt replacements using as little as 5 watts. They are often dimmable, although not to the same degree as incandescent bulbs. And the quality of light can be very good, although the color of cheaper bulbs is often too warm or too cool, and may vary greatly between bulbs. They are also the most expensive type of general task lighting.


In this analysis, there were a number of changes that were made.

  • Any general task lighting that did not need dimming was replaced with CFL.
  • In several cases it made sense to replace incandescent bulbs with LED, due to a payback timeframe that was under one year. In this case a number of 60 watt bulbs that burned for about 10 hours a day were replaced with 5 watt LEDs. While the bulbs were expensive to buy ($20 each), the energy savings in the first year should more than offset the cost. Since the bulbs have a five-year warranty, there should be significant savings over the life of the bulbs. The math is outlined below.

Cost per 60 watt bulb at 10/hours day, 5 days a week: $24

Cost per 5 watt bulb at 10/hours day, 5 days a week: $4

Bulb cost: $20

Net cost for first year: $0

Net savings over five-year warranted life: $80

Wireless thermostat control

While we were researching energy, it made sense to take a look at heating and cooling. Although we don’t have comparison figures here, we found that some inexpensive new technology enabled a significant reduction in heating and cooling draw, due to smart controls.

It’s not uncommon for photographers to have access to dedicated spaces for either shooting or editing images. These spaces may have dedicated thermostat controls. Remote wireless control of these thermostats may be able to reduce the heating and cooling costs for these spaces.

Thermostats that are programmable for time-of-day adjustments have been common for decades. These work well for spaces that have very predictable cycles of usage. If the usage of the space is not standardized, however, these devices may apply heating or cooling at unneeded times. Wireless controlled thermostats can overcome this shortcoming, particularly if the thermostat can be controlled with a smart phone or other internet-connected device. Until recently, this capability only existed in expensive home automation systems.

Equipment tested

This study is based on the use of the 3M Wi-Fi Remote Programmable Thermostat, as shown in Figure 2. This unit is available at Home Depot stores and the Home Depot website for about $100. It can connect with an ordinary wireless router. It’s possible to run multiple devices on the same wireless network, and control them from computers, smartphones, and iPads.

´┐╝Figure 2 This 3M Filtrete thermostat offers programmable heating and cooling control, as well as wireless connectivity. It can be controlled by a computer, tablet or smart phone.


The use of a wireless thermostat did more than simply reduce energy usage for the studio. It encouraged an entirely different attitude about the heating and cooling of the space. Prior to the installation of the thermostat, it was necessary to proactively heat and cool the studio, so that it would be ready for use. Once the remote thermostat was installed, it became much easier to preheat or precool the studio only when it was about to be used.

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Last Updated September 22, 2015