Lumen (lm): Actual Measurement of Light

Lumen is the total amount of visible light emitted by a light source in all directions. So "how bright is this fixture?" The real answer to the question is lumen. The higher the lumen of a fixture, the more light it produces. This is the first value you should look for in an LED bulb box.

A few rough references: a candle puts out about 12 lumens, an old 60 W incandescent bulb gives ~700 lumens, a 100 W incandescent bulb gives ~1300–1500 lumens. A modern 60x60 office panel produces light between 3600–4400 lumens.

Watt (W): Power Consumed, Not Light

Watts are the electrical power drawn by the fixture — it represents the energy it consumes, not the light it produces. Since wattage and brightness were roughly parallel in the incandescent bulb era, the question "how many watts?" The question was useful. However, this equality is broken because LED produces much more light by drawing much less power.

Comparing Lumens to Watts

When replacing old incandescent bulbs with LED counterparts, it is necessary to look at lumens rather than watts. The table below shows approximate equivalences:

For example, the Pelsan 9W E27 LED lamp delivers approximately 806 lumens, effectively replacing the classic 60 W incandescent bulb — and drawing one-sixth the power. This is exactly the saving logic of LED.

Lux (lx): Illuminance Falling on the Surface

If lumens is the total light produced by the fixture, lux is how much of that light falls on a particular surface. By definition, 1 lux = 1 lumen / 1 square meter. In other words, while the same fixture provides high lux in a small room, when spread into a large hall, the brightness (lux) per square meter decreases.

Lux is the value required by the standards. TS EN 12464-1 indoor workspace standard determines the minimum illumination level in lux for each space:

Candela (cd): Direction-Dependent Light Intensity

Besides lumen, watt and lux, there is a fourth unit that is frequently confused: candela (cd). If lumen is the total light emitted by a source in all directions, candela is the intensity of that light in a specific direction. The difference comes down to how the fixture distributes light. Consider two spotlights delivering the same 1000 lumens: one that concentrates the light into a narrow cone produces a high candela in that direction (a bright, far-reaching beam); if the other emits light at a wide angle, it gives lower candela in all directions (soft, wide illumination).

In practice, the home and office buyer is mostly concerned with lumens and lux; Candela stands out in applications where light is directed, such as street lighting, LED projector, spot and accent lighting. A product's light angle (°) and candela value are read together: narrow angle and high candela give a distant emphasis; Wide angle and low candela provide soft general illumination.

Lux and Distance: Why Does Light Weaken with Distance?

An important feature of Lux is that it decreases rapidly with distance from the source. The reason for this is the inverse square law: the illuminance created by a point source on the surface decreases inversely proportional to the square of the distance. In other words, when the distance doubles, the brightness decreases to a quarter. With the formula: E = I / d² (E illuminance-lux, I light intensity-candela, d distance-meter).

That's why a high-ceiling warehouse or factory requires much more powerful (high lumen) fixtures than a low-ceiling office to provide the same floor lux. As the ceiling rises, the lumen of the fixture should increase or the number of fixtures should increase; For this type of spaces, you can look at the high ceiling fixtures category. The fast lumen formula (area × lux) roughly captures this effect; However, for high ceilings, a project that takes the ceiling height into account is required.

Lumens/Watt Efficiency: A Measure of Efficiency

The lumen/watt (lm/W) value shows how efficient a fixture is: it is how many lumens it produces per watt it draws. The higher this value, the less energy you get the same light.

• Incandescent bulb: ~12–15 lm/W (most of the energy goes to heat)
• Fluorescent: ~60–90 lm/W
• Modern LED: ~100–150 lm/W and above

A Simple Calculation: How Many Lumens Does My Room Need?

The practical formula for a rough estimate is:

Required lumens = Area (m²) × Target lux

1. Measure the area. Example: An office of 4 m × 5 m = 20 m².
2. Set target lux. 500 lux for office with computer.
3. Multiply. 20 × 500 = 10,000 lumens total need.
4. Divide by luminaire. With 60x60 panel of 4000 lumens: 10,000 ÷ 4000 ≈ 3 luminaires.

Lumen Requirement by Location: Quick Table

By applying the "Area × target lux" formula to common locations, you can roughly foresee how many lumens are required. The following table gives approximate total lumen requirements for typical room sizes:

Do not expect the total lumen in the table from a single fixture; Dividing the need into multiple fixtures gives more uniform (homogeneous) illumination and reduces shadows. For example, the need for a 7,500 lumen office is distributed much more evenly with three 2,500 lumen fixtures. In areas such as kitchens and bathrooms, it is also necessary to add local lighting for the counter and in front of the mirror.

What Values Should You Look at in the Box?

When buying an LED bulb or fixture, a few values on the box are enough to make the right choice. Don't get hung up on Watts; The real information is in the other lines:

From two products with the same lumen value, choosing the one that suits your Kelvin needs, has a high lm/W and a sufficient Ra will provide both the right light and a low bill. The light angle is often overlooked: a narrow-angle spotlight is ideal for emphasis, while a wide-angle fixture is required to illuminate a large room.

Is Lumen Alone Enough? Other Quality Measures

Lumen answers the question "how much light", but it does not tell the quality of the light on its own. Two fixtures with the same lumen can give a very different lighting experience. To make the right choice, the following criteria should also be considered in addition to the lumen:

• Color rendering (Ra / CRI): How accurately colors appear. Ra≥80 is preferred in interior spaces, and Ra≥90 is preferred in display and textiles. At low Ra, colors appear faded and inaccurate.
• Color temperature (Kelvin): The hue of the light. Yellow Light (2700–3000K) is suitable for home and recreational areas, Daylight (4000–4500K) for offices and kitchens, White Light (5000–6500K) for technical and industrial areas.
• Glare (UGR): The degree to which light strains the eyes. UGR≤19 is targeted in the office; High UGR causes discomfort in front of the screen.
• Light distribution (angle): Narrow angle emphasis, wide angle general illumination. If the same lumen is spent at the wrong angle, it will not reach the floor.

So "highest lumen" does not always mean "best fixture". Aim; It is to deliver the right lumen to the floor at the right color temperature, with sufficient Ra and low glare. To choose the Kelvin value that determines the tone of the light in detail, you can check our color temperature guide.

How Many Lumens Was the Old Bulb? Quick Response

For years, we chose the bulb by watt; When switching to LED, it is necessary to convert the measurement to lumen. The table below gives the approximate lumen equivalent of older incandescent bulbs; When buying LED, you can achieve the same brightness by looking at this lumen value:

As can be seen, the LED gives the same light with approximately one-sixth the power; The difference is reflected directly on the invoice.

Impact on Invoice: Converting Watts into Money

We said that watts indicate consumption, not brightness; So how is this reflected in the invoice? The calculation is simple: consumption (kWh) = power (kW) × operating time (hours). The annual cost is this consumption multiplied by the electricity tariff. Let's compare an incandescent and LED fixture that works 8 hours a day:

Two fixtures emitting the same light produce a difference of approximately 248 kWh per year — for just one spot. Considering dozens of luminaires in a business, switching to LEDs with high lm/W pays for itself in a short time. This is the monetary equivalent of the advice "look at lumens, not watts".

Light Decreasing Over Time: Lumen Protection (L70 / L80)

LED fixtures lose light slowly over time, rather than flashing suddenly. Therefore, life is defined by when the luminous flux drops to a certain rate rather than "how many hours it burns". Frequently used expressions are L70 and L80: L70 is the number of hours in which the luminaire is reduced to 70 percent of its original light (for example, 50,000 hours); L80 is the 80 percent level.

That's why a "maintenance factor" is used in a project: when the fixture is new, the targeted lux is kept slightly high so that the required minimum lux on the floor is maintained even after years when the light decreases. When choosing a quality LED, looking not only at the initial lumen but also at the L70/L80 life value given by the manufacturer guarantees correct illumination in the long term.

Seeing Three Units Together

In summary, these three units complete a chain: the luminaire produces lumens, draws watts of energy, and ultimately creates lux on the surface. Correct lighting; The aim is to achieve the target lux by providing sufficient lumen with the minimum wattage. For the color temperature that determines the tone of light (yellow/daylight/white), see Kelvin guide; For product families, you can review lighting category.

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