Lumens to Watts – how to choose the right light bulbs, brightness and colour

Lumens to Watts – how to choose the right light bulbs, brightness and colour

What Wattage is right?
For decades, we’ve been buying light bulbs according to wattage. But in recent years choosing light bulbs has become far more confusing – you knew roughly what you were getting with a 40, 60 or 100 wattage filament bulb.Nowadays, energy saving bulbs produce far more light, less heat, whilst consuming less energy (Watts). They come in varying technologies, such as Compact Fluorescent (CFL), Halogen and LED and they last much longer – up to 25 years for LEDs! Defining the brightness, or light output of bulbs is changing from wattage equivalents to lumens. Lumens is an accurate way of measuring the light output of bulbs – brightness is what we perceive, luminance is what we measure. However, this can be a little confusing! Most of us have a preconception of how bright a 100-watt incandescent bulb is even though this can vary tremendously between soft white and clear glass bulbs. On average, an incandescent bulb produces around 14 lumens per watt, compared to 63 lumens for energy saving compact fluorescents (CFL) and 74 for LED bulbs. Some of the most energy to light efficient LED bulbs are now reaching over 120 lumens in Energy Star tests.

As energy efficient, low-watt light bulbs like CFLs and LEDs have become readily available, watts have become an unreliable metric for selecting bulbs. Instead of focusing on wattage, which measures power or energy use, manufacturers are indicating the brightness of their energy efficient bulbs according to lumens, which measure light output. So while we may be accustomed to shopping for bulbs according to wattage, lumens are actually a more accurate measurement of how bright your light will be.

How many lumens are in a watt? Because lumens measure brightness and watts measure energy output, there is no simple method for converting wattage to lumens.

With energy efficient lighting like LEDs and CFLs, how many lumens are in a 60W bulb or 100W bulb depends on the lumen output of the bulb, not its energy use. Don’t despair! Measuring and labelling light output instead of energy use actually makes it easier for you to find the right energy efficient bulb for your space. Use this chart to determine how many lumens you’ll need from your next light bulb. For example, if you typically purchase 60W incandescent bulbs, which produce about 830 lumens, consider purchasing a lower energy alternative like a 45W halogen bulb, 13W CFL, or even a 11W LED bulb to achieve the same brightness.

Data sources: American Association of Physics Teachers 1996 and Energy Star 2016

What else can affect brightness perception?
The colour of light can also affect how bright a light appears, even if the lumens are the same. Bulbs that are nearer to daylight (bluer or cooler in colour) sometimes appear brighter than yellower coloured lights.

Choosing the colour temperature of bulbs
Choosing the right colour is dependent on the atmosphere you’re trying to create within your room, or what the space you are lighting is used for. Light colour is measured using a temperature scale called Kelvin (K). Incandescent bulbs are around 2700-3000K and produce a yellower warm/soft light, great for creating a relaxed ambiance. For whiter light – more akin to daylight – good for kitchens and workspaces, bulbs labelled between 3500-4100K would be best. Reading lights tend to be marked 5000-6500K these appear much bluer and perceived as brighter.

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