We’ve all struggled at one time or another in a room that was just too dim to see what we were doing properly. Whether reading in the living room or chopping veg in the kitchen, the right amount of light is critical to the task.
It used to be you would just up the wattage of the bulb to get more light. A 100-watt bulb would flood you with more light than a 40-watt bulb.
Today, you need to know how many lumens will give you the amount of light you need because watts are no longer a consistent measure. A 12-watt LED bulb can give you 1,200 lumens, while you might need 18 watts to get the same light from a CFL.
So just what is a lumen and how do you use it to determine which bulb to buy? When you want to create a well-lit space, understanding lumens is the first step to getting your room bright enough.
Let’s take a look at lumens and how they fit in your lighting calculations.
Shedding Light on Lighting Terms
Before you start calculating the LED lumens you need, you should probably know and understand a few lighting terms. These help you understand what you’re reading on the box of bulbs you pick up.
When we talk about how bright a light is, we’re referring to the lumens. They’re a measure of how much visible light is emitted by the bulb and are based on how humans see light. That makes them a useful standard for figuring out comfortable and practical levels of light.
A standard 100-watt incandescent bulb sends out about 1,500 lumens. All the other measurements used in lighting are based on lumens. It’s the best number to look for on a box of bulbs since it gives you the best picture of how bright the light will be.
This unit of measurement is more closely tied to the perceived brightness of a light and equals one lumen per square meter. Because it’s tied to area measurements, we use it to help us figure out the proper amount of light for a specific space. You can think of it as the intensity of light within an area.
As light travels, it disperses in an area. The further it travels, the more dispersed it gets. So when lumens are concentrated in a smaller area, the light will appear brighter because the lux are more concentrated.
While our old incandescent light bulbs were measured by watts, it isn’t really a measure of brightness. Rather, watts tell us how much energy is used to reach a certain level of light.
Different types of bulbs have different lumen-per-watt ratios, which is why LED lights can use so much less energy while producing the same amount of light.
The introduction of LED and CFL bulbs means we can get more light out of a bulb while using less energy. This efficiency is measured by the number of lumens produced for each watt consumed. Higher lumens at lower wattages give us the most efficient combination for lighting.
Calculate How Many Lumens You Need
Now that you have an idea of how lumens relate to light brightness, it’s time to do the math to figure out how many lumens - and thus bulbs - will get you the brightness level you want in a particular room. Here are the numbers you need to gather and know to do the calculation.
Because lux is related to area, you need to start by figuring out the area of the space you’re trying to light. Calculating the square meters of your room is a simple piece of math. You simply need to multiply the length of the room by the width.
If your room has some odd shapes, you can break the room up into more even square and rectangles to figure the square meterage.
Room Type and Purpose
Not every room needs the same amount of light. You do a lot of fine tasks that require more light in the bathroom and kitchen. But you don’t need quite so much light to see your food in the dining room or while watching your favourite show in the den.
Here are the ranges of suggested average lux needed by space for a few rooms in your house.
Hallway - 100-300
Living room - 700-1000
Bedroom - 400-600
Dining room - 500-700
Kitchen general - 1000-1500
Kitchen task - 1500
Bathroom - 1000-1500
Your Lumens Calculation
Now that we know the size of the room and roughly how many lux you should need, we can figure out how many lumens you need to reach your target brightness level.
The basic formula is to multiply the square meterage of the room by the lux requirement. As an example, a 10 square meter living room that needs 100-200 lux would need 1,000-2,000 lumens. However, a 10 square meter kitchen at 300-400 lux would need 3,000-4,000 lumens.
Ready to Brighten Your World?
With incandescent light bulbs, the wattage gave us an idea of how bright the light would be. New light sources like CFL, LED, and halogen produce different amounts of light per watt, which makes lumens a more reliable way to figure out how many bulbs we need in a space. Knowing the room size and how bright you want it allows you to do the calculation.