How to Use a Light Meter to Set Appropriate Light Levels

how to use a light meter for rightsizing lighting

Lighting in your home is among the top five energy users, alongside your fridge, HVAC, water heater, and clothes dryer. Most people know by now to swap out lights for more efficient LED models (or CFLs, if LEDs aren’t available, but CFLs are less efficient, contain mercury, and don’t last as long as LEDs). However, most people don’t think about the fact that the most efficient lighting may be no lighting at all. In many cases, areas of your home or business may be overlit, making it not only uncomfortable on your eyes, but also a complete waste of energy.

The process of rightsizing your lighting has been referred to as “delamping”. Effectively, if you have too much light in an area for the tasks that are done in that area, you can remove one or more of the bulbs and drop energy use substantially (and more importantly, infrastructurally, so that occupant behavior is less important…this is huge for small businesses where employees are busy, and for parents of children who like to leave lights on).

Check out this article on proper light levels, just to give yourself some background on the topic. Then, let’s get on to reducing your energy consumption by removing lights where appropriate!

Now, let’s review the proper way to measure the lighting levels in your home:

To do this you’ll need a light meter (if you don’t have one, you can bookmark this page and use that link to purchase a light meter). Here are the steps to assessing the lighting levels in your home:

1. Measure the ambient light in your desired room. Be sure that you have all the lights in the room turned off. Now take your light meter and get a baseline measurement for the room. You’ll use this baseline number when determining how much synthetic light is being contributed by the light bulbs in the room.

How to use a light meter

2. Turn on the lights you’d usually use while occupying the room. Give your lights a minute to reach full illumination, especially if you have CFLs which require a minute to power up fully. Now, take your light meter and measure the light level of the room again, you should get a reading that is higher than your initial baseline measurement.

how to use a light meter to measure ambient lighting

3. Take the difference between your ambient and illuminated lighting levels and compare it to the guide above. By subtracting the ambient light level from your illuminated level you’ll get what’s called a differential or delta. Which is the amount of light being created by the light bulbs in your room. Or, the amount of light illuminating the room at night, when there is no ambient light. For example, if you measure the ambient light in room and the reading comes out to 100 lux, and after you turn on the lights you get a reading of 300 lux, the differential (or delta) would be 200 lux. If the differential (or delta) reading for the room is higher than is necessary for the tasks being performed in that room, odds are this can be remedied by simply removing some light bulbs. Conversely, if the differential is too low, you may need to add light bulbs to your fixtures or put a lamp in your room to reach the desired lighting level.

Next Step: Delamping

Now that you’ve determined the right amounts of light needed in a particular area, it’s time to start saving money. The process of rightsizing a lighting fixture is often referred to as delamping. It’s about what it sounds like…except more elegant, and scientific. A very common place in the home that delamping helps to save energy is in the bathroom, where vanity lighting fixtures are historically stupid bright. I took a reading on this bathroom with my light meter and found the lighting to contribute over 400 lux….way more than is needed even for high performance tasks that require precision.

Delamping Before: 400+ lux, 360 watts
Delamping (before): 400+ lux, 360 watts

In addition to it being too bright, it’s costing the occupant through high energy bills. This fixture had six 60 watt vanity bulbs in it, totalling 360 watts. Completely absurd. I delamped this fixture by simply unscrewing every other bulb, and replaced the remaining incandescent bulbs with high efficiency LEDs that use 1.7 watts each. Here’s the result:

Delamping after: 200+ lux, 5.1 watts
Delamping (after): 200+ lux, 5.1 watts

Boom. Just like that, 355 watts less power, and a barely noticeable difference in light output. ROI? Huge.

If you’re looking for more ways to save money around your home, check out our green home improvement projects: Green Living Ideas, after all, is a top 20 home improvement website! Also, see here for ways to reduce your energy on your:

  1. dryer (and also, tips for effective indoor line drying)
  2. refrigerator (how to clean your condenser coils)
  3. air conditioner maintenance tips for energy efficiency
  4. water heater

Photos courtesy of Small World Labs and Pono Home

About the Author

Scott Cooney (twitter: scottcooney) is an adjunct professor of Sustainability in the MBA program at the University of Hawai'i, green business startup coach, author of Build a Green Small Business: Profitable Ways to Become an Ecopreneur (McGraw-Hill), and developer of the sustainability board game GBO Hawai'i. Scott has started, grown and sold two mission-driven businesses, failed miserably at a third, and is currently in his fourth. Scott's current company has three divisions: a sustainability blog network that includes the world's biggest clean energy website and reached over 5 million readers in December 2013 alone; Pono Home, a turnkey and franchiseable green home consulting service that won entrance into the clean tech incubator known as Energy Excelerator; and Cost of Solar, a solar lead generation service to connect interested homeowners and solar contractors. In his spare time, Scott surfs, plays ultimate frisbee and enjoys a good, long bike ride. Find Scott on