Technical Guide | Lumen (Luminous Flux)

What is Lumen (lm)?

Lumen, often denoted by the symbol "lm," is the unit for measuring the amount of visible light emitted by a source, such as a light bulb. In simpler terms, it quantifies the brightness of a light. It's not about the energy the light bulb uses (that's watts) but rather how bright the light appears to our eyes.

Historically, people used watts to gauge a bulb's brightness, mainly when incandescent bulbs were the norm. However, with the rise of energy-efficient lighting like LEDs, the focus shifted to lumens.

Influence of the luminaire on luminous flux

Luminous flux, measured in lumens, tells us how much visible light a source emits. However, the actual brightness we perceive in a room doesn't solely depend on the light source (like a bulb) alone. The fixture or luminaire in which the bulb is installed can significantly influence this output.

Material absorption (diffusion):

Materials used in a luminaire, such as reflectors, opal filters, lenses, or any surfaces, can absorb some amount of light. This absorption means that not all the light emitted by the light source reaches the room. The type and quality of materials can determine how much light gets absorbed. For instance, a shiny, mirror-like reflector will reflect more light into the room than a matte or dark-colored one.

Orientation of light:

The design of the luminaire can dictate the direction the light takes. Some fixtures produce a narrow, focused beam (like spotlights), while others give off a more diffused, spread-out light. The directionality can affect how the space is illuminated and can create specific lighting effects.

Lumen in practice

The lumen value gives a direct indication of the brightness of a light source. A higher lumen value means the light source is brighter, while a lower value indicates dimmer light. When selecting lighting for different parts of a home or any space, understanding the lumens required can guide your choice:

600/800 lm for integrated spotlights

These are suitable for areas that require intense, focused lighting. Kitchens, where detailed tasks like chopping are performed, or larger, higher spaces can benefit from such high-lumen outputs. The spotlight design ensures the light is directed where it's most needed.

300/600 lm for general lighting

This range is ideal for general or ambient lighting. Suspended luminaires, often seen in dining areas or living rooms, fit this category. They provide enough brightness for everyday activities without being overpowering.

150/200 lm for accent lighting

These are apt for accent or occasional lighting. Think of table lamps or bedside lamps, where the goal is more about ambiance or a subtle light source rather than full illumination.

Dimming and Lumen

Dimming refers to the adjustment or reduction of a light source's brightness. As you dim a light bulb, you effectively decrease its lumen output. Conversely, increasing the brightness on a dimmable light source raises its lumen count. It's essential to understand this relationship, especially when choosing lighting for spaces where mood or ambiance is crucial.

In a living room, you might want bright lighting (high lumens) for reading, but later in the evening, prefer a softer, dimmed ambiance for watching movies. A bulb or light fixture with integrated LED with adjustable lumen output (through dimming) offers this flexibility.

Learn more about dimming

Kelvin and Lumen

Lumen measures the brightness of a light, while Kelvin determines its color temperature (warm yellow to cool blue). While they function independently, the perceived brightness can be influenced by color temperature. For example, cooler lights (higher Kelvins) often seem brighter than warmer ones, even with the same lumen output. When choosing lights, both brightness (lumens) and color temperature (Kelvin) play roles in setting the desired ambiance and functionality.

Learn more about color temperatures

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