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What Are Lumens And Why Are They So Important?
Lumens. Having a good understanding of what they are and what they measure is crucial for anyone seeking to install a lighting system which is both appropriate for and effective in a given space. But, despite the undeniable importance of lumens, they remain something of a mystery to many people.
What’s the consequence of this? Ultimately, by keeping ourselves ‘in the dark’ about the practical impacts of lumens, we risk selecting light fittings and fixtures which have a negative effect on how we experience an environment, be it a shopping centre, private residence, office, coffee shop, hotel, school or otherwise.
It’s worth noting, though, that any knowledge of lumens must be used alongside an understanding of several other important design considerations. To specify lights which add real value to a space, it’s vital to specify lumen output in relation to variables such as colour rendering index (CRI), correlated colour temperature (CCT) and luminance amongst others…all of which we will explore in greater detail in separate articles.
What Are Lumens?
The definition of lumens, as it is given in the Merriam-Webster Dictionary, states that they are “a unit of luminous flux equal to the light emitted in a unit solid angle by a uniform point source of one candle intensity.”
Now, with explanations such as this being most peoples’ first and only introduction to the idea of lumens, it’s perhaps clear why there is such a high level of uncertainty surrounding what they are and why they matter!
In simpler, less technical terms, lumens (denoted by ‘lm’) are nothing more than the measure of the total amount of visible light that is emitted from a given light source. This means that the higher the lumen rating of a lamp is, the brighter it will appear to the human eye.
The key thing to take away here is that lumens represent the amount of luminous flux emitted from a lamp…the more lumens, the brighter the light!
What About Watts?
Wattage (denoted by ‘W’) is the SI unit used to measure the output of incandescent lightbulbs. It refers, not to the amount of light emitted by a light source, but to the amount of electrical energy that is required to power it. However, as became clear with the development of LEDs, Wattage isn’t a direct representation of a lamp’s light output.
For example, thanks to huge technological advancements, a low-wattage LED can deliver the same light levels as a high-wattage incandescent alternative. Why is this so? Because LEDs are more efficient than incandescent bulbs, meaning that more of the electrical energy they consume is converted to light energy and less ends up being wasted as unwanted heat energy.
Watts are still a useful measure, then, but only when the wattage of a light source is considered in relation to its lumen output.
Useful (And Useless) Lumens
The idea of lumens being both useful and useless (or wasted) takes on particular relevance when we think about spotlights, task lighting and other ‘directional’ lamps. Why? Because the lumen output of a light source is calculated by measuring the amount of light that is emitted in all directions…not just that which is emitted in the direction it’s pointing. This means that light sources such as fluorescent tubes and incandescent lamps may not deliver all of their brightness directly onto the target area or product.
This is why experts introduced the ‘useful lumens rating’. This is a measure of the light that is emitted in a 90° cone from the direction in which the bulb is pointing. By focusing solely on the useful lumens, we’re able to determine how bright a light source will actually appear in practice rather than in theory.
What Lumen Output Is Best?
That depends entirely on the space in question – its location, its size, the amount of daylight it receives, its function, its interior décor, its users…the list goes on. Yes, as is recognised by CIBSE in official publications, different environments require lighting systems with different lumen outputs in order to ensure that the best ambience for a particular environment is achieved. In fact, in a previous blog post, we shared our insights on the psychological impact of light and on how lighting temperatures and intensities are some of the most influential factors in determining how we experience a space.
Hotels, for example, need to think about the type of accommodation they offer (budget vs. luxury) and about the varying needs of their guests (sleeping, dining, reading, socialising and so on). That is, people require dramatically different light levels when drinking with friends in a bar compared with when they are reading a magazine.
Additionally, research carried out in New Zealand highlighted that the ambient lighting requirements of a space differ depending on the values particular to its target audience. This study showed that:
- Retailers that sell essential goods, fast-food outlets and convenience stores perform best when using lights that deliver between 500-800 lumens per m² (measured in lux) at floor-level. This is because such levels enable customers to easily navigate the space, quickly select the products they need and then leave having achieved their original objective.
- Mid-range retailers, restaurants and cafes are proven to perform better with slightly lower lux levels of between 300-500 at floor-level. This is because less intense lighting creates a more atmospheric environment, ultimately giving customers the impression that the brand with which they are engaging is of a higher quality.
- Luxury retailers and high-end hotels should choose lighting systems with even lower lumen outputs. To encourage guests to feel as though they are in an intimate environment, the ideal range is between 300-500 lumens per m² at floor-level. Then, to enhance the impact of this low-level ambient lighting further, key areas or products can be highlighted using accent lighting. This effectively creates drama within a space by juxtaposing brighter areas with those that are less so.
Hopefully, after reading this blog post, you feel more confident in your understanding of what lumens are and why they’re so important when designing effective lighting solutions.
If you’d like to learn more about lumens, about LED technology more generally or about how the strategic management of both of these elements can ‘make or break’ any type of space, then our team of experts will be happy to advise you.
Using our experience, we can provide individualised guidance based on the specific physical characteristics of your space and the commercial objectives you are hoping to achieve.