What Is Light Output Ratio?

LEDs are fast taking over the preferred method of lighting up homes, offices, retail spaces, and more. It is no doubt a highly efficient and energy-saving alternative to traditional bulls.

Simultaneously, the technology is not as simplistic as white-hot filament heating up to give off the light!

LEDs are more akin to computers than to light bulbs. That’s why purchasing and setting up an ideal light system in your space requires a little more reading and, in some cases, calculating the best numbers.

Light output ratio (LOR) measures the efficiency of the fixtures or luminaires that house a light bulb. The measurement is a percentage, derived by dividing lumens output from the luminaire by the lumens output from the bulb.

What Is Light Output Ratio?

Simply put, Light Output Ratio, or LOR, is a number that tells us how much light from a bulb or lamp is actually emitted once it is placed inside a fixture or luminaire.

Or, a little less simple, LOR is described as “the ratio of the luminous flux of the luminaire to the lumens of the lamps used” according to standardizing code DIN/EN 13032/2.

It is expressed as a percentage.

For example, you have a bulb with a lumen rating of 1000 Lumens and use it in a fixture with a LOR of 80%.

You would essentially receive 800 Lumens from the fixture once the bulb is installed, while 20% is lost lumens.

In consumer specification lists, it is also sometimes referred to as Luminous Efficacy.

What Does LOR Tell You?

So as a regular user of bulbs in homes, what does LOR mean for you and exactly what does it indicate….

The LOR is a measure of how economical a fixture is by measuring how much light is ‘lost’ or trapped inside a luminaire.

It’s a quite simple enough concept to understand. When you have a bare bulb, it emits light in all directions except towards the base or screw part.

No light is lost, and this is a bulb at its 100% luminosity or the lumen rating that you purchased it for, and can usually read on the box.

The problem arises when you place the bulb into a fixture or fitting, and then observe the net light that is being actually emitted and which you can see, due to the construction of the fixture.

Once you calculate the new output or luminous flux of the luminaire, you can compare it to the intended lumens, and derive the Light Output Ratio.

Good downlight luminaires have a LOR between 80% to 90%. Some building standards set a certain minimum percentage of LOR at 60%, that a fixture can have to avoid wasteful use.

Imagine having bright high lumen bulbs in fixtures that eat up more than 40% of the light! That defeats the purpose of having any energy-saving bulbs in the first place.

Designers use the LOR reading to decide the best kind of fixtures and fittings that will look good, without taking away the efficiency of the bulb inside.

Always keep in mind that despite what some manufacturers might claim, no luminaire will have a LOR of 100%. Some light is still lost inside the fittings and fixtures.

Why Is LOR An Important Measure?

Just like any setup or process, the sum is only as strong as its weakest part.

No matter how high quality your bulbs are, if the wiring, switches, or luminaires aren’t up to par or work as effectively, your bulb’s output will also suffer.

Now that you know a little bit about how light output ratio can radically affect the brightness of your bulbs, you can make a smarter decision about the products around the bulb.

Let’s suppose you’ve been doing some research and decided that for your living room, you would need bulbs of 1500 lumens to have the area bright and well-lit.

Your most logical next step would be to purchase bulbs with approximately 1500 lumens.

What you didn’t realize and account for is the light output ratio of your light fixture, and probably don’t even know how much that number is, in the first place! A low LOR would mean trouble.

As a result, your room is quite dimly lit at the end of your project, and you can’t quite put your finger on the reason.

The bulbs obviously lost light within the fixture, bringing down the room’s actual usable lumens or brightness.

This is where knowing about LOR could have helped you achieve a more realistic end result. Buying higher lumen bulbs would have very simply fixed the problem, and in hindsight, seems very straightforward.

How to Calculate Light Output Ratio?

So it definitely sounds like an important enough specification to know before purchasing the fixture or new bulbs.

But knowing this, how do you measure the LOR, if, for example, it is not mentioned on the spec sheet.

Or if you suspect that your manufacturer has claimed a very wrong figure.

One thing you need to keep in mind is that LOR is usually used for luminaires that use fluorescent lights that emit light both upwards and downwards.

On the other hand, LED luminaires calculate luminous efficacy as lumens per watt. But this is not always the case, LED luminaires can also measure or list LOR depending upon the manufacturer’s preference.

There is not a lot of regulation in the industry for these kinds of readings.

To get a basic idea of LOR, you can measure lumens yourself that are being output, using a lux meter (Amazon).

By determining the lumens being output once the bulb is in the housing and dividing it by the rated lumens of the bulb, you can calculate the LOR of the fixture.

The more accurate way of measuring LOR as a complete picture is possible by Photometry, a study that uses different measurement techniques for LED luminaires.

Professionals can do a thorough job and provide a more distinct measurement of how much light is being wasted upwards and downwards from the fixture.

Final Words

Figure out the LOR for your fixtures and light housings to achieve maximum light output or purchase the correct brightness lamps for the effect you want.

Have you read your LED or luminaires’ specifications page and come across LOR percentages?

Do you plan to measure the lumens output of your fixtures in your office or homes yourself?