People often make the mistake of using the word "bright" or "brighter" to convey two different meanings.
For example, residents of a neighborhood that just switched over to LED from traditional street lights may complain about the lights being too bright. These lights have more than likely been sized properly to be compliant with the local ordinances.
So why is this happening all over the country?
The answer may be that the residents are confusing their Kelvins for Lumens.
The difference between Lumens and Kelvin is that Lumens is used to measure the brightness output of a certain light fixture while Kelvin is a unit used to measure color temperature, and most people outside of the lighting profession often mistake the two.
Lumens: A unit measuring Brightness Levels
Lumens is a unit of measurement used to measure the amount of light (brightness) coming from a certain source. The higher the lumen rating, the brighter the light. This unit of measurement has been gaining prominence over the past 20 years due to shifts toward LED light sources.
LED lights are more directional in nature and are equipped with multiple diodes aiming at the emission of light in a specific direction instead of all directions like traditional lighting sources. Directional lights are more concentrated in nature and as a result, produce a higher lumen output.
Before LEDs had gotten so popular, people would indicate brightness just by simply using wattage instead of the actual brightness levels. This was a lazy way to go about it as even back then, different light sources would not emit the same amount of brightness per watt.
However, LED's insane efficiency made it a necessity to shift the language of the industry to use a measurement that actually represents the brightness levels instead of the amount of electrical energy used on the particular fixture in question.
There is even a practice out there where companies and industry insiders use "Watt Equivalent" for LED instead of simply using Lumens. Their thinking is that the general consumer is so used to wattage numbers that switching to Lumens is too much of a leap.
However, things are improving and it's about time. Nowadays, it's common to see industry professionals and even homeowners specify their lighting needs in terms of lumens as opposed to watts.
Kelvin: A unit that measures the Color Temperature of the light source
Unlike Lumens which measure brightness levels, Kelvin is a unit of measurement used to indicate the color temperature of light fixtures. It ranges from Warm temperatures starting at 2700 Kelvin (or 2700K) to much cooler temperatures up to 6500 Kelvin. As a point of reference, daylight is around 6500 Kelvin, while your old residential light bulb is on the warmer side of the spectrum at 2700K.
Kelvin Rating can be much higher than 6500K but for the purpose of light fixtures, they rarely go past this figure and might even be considered to be non-compliant in most jurisdictions.
By default, LED light bulbs should have a Kelvin rating of around 5000K as LED tends to be much cooler. However, LED technology has advanced so much in the past decade that manufacturers have been able to create LED technology with much warmer light output. It's not uncommon today to walk in at home depot and be able to purchase a 2700K led light bulb.
This is a key to the mass adoption of LEDs as the go-to light source for most applications. While LED was more energy efficient, and cheaper in the long term, it was limited in decorative applications as the light was simply too cool. While seasoned designers can still notice the difference between a 2700K incandescent & LED bulb, the average consumer would not.
The availability of LED fixtures with multiple Kelvin options removed the only "excuse" most people would have against LEDs and as a result LED sales and adoption skyrocketed as most national and local authorities are pushing for LED adoption since it's much better for the environment as a whole.
Lumens vs Kelvin: What causes the confusion?
As we've laid it out for you so far, Lumen and kelvin are two different measures of light and are used to describe different aspects of a light source. Lumen measures the amount of visible light emitted by a source, while kelvin measures the color temperature of that light. Because these two measures are often used together, it can be easy to confuse them.
When an untrained person refers to a light source as "too bright", they can be rightly referring to the actual level of brightness of said light fixture and they would be technically correct. However, the average person also tends to refer to a light being "too bright" or "not bright enough" when they've noticed a change of color temperature to what they are used to or are expecting.
Differentiating between color temperature change and brightness levels is simply not an easy task for the untrained eye. This is an issue that will only get resolved over time as the general public becomes more aware and better exposed to different color temperatures in their everyday lives.
Shopping for LED lights is one example of how the general public is starting to understand the difference between lumen and kelvin. 20 years ago, when a homeowner was shopping for a replacement light bulb, they would simply run down to their local hardware store and get a standard replacement bulb without having to make any decisions on specs.
Wattage was the only spec that would matter to them and if we're being honest this was only sought out by the savviest homeowners or Do-it-Yourselfers.
However, if a homeowner goes to a Lowe's or Home Depot today, they will be presented with LED light bulbs with different color temperatures with possibly different price points. Curious shoppers will naturally ask themselves which of these bulbs is better for them and, more importantly, why one costs slightly more than the other.
This process has put people in a position to understand the difference between lumen and kelvin and has raised the overall understanding of lighting technology by the general public.