What is a light trigger? How does light level affect fan operation?

How does the fan know that the light has been switched on?

It uses a light sensor. The sensor compares the brightness of the light falling on its element with a selected sensitivity level. If the brightness reaches a sufficient level, a “light trigger” occurs and the fan starts operating according to its preset scenario.

Lux and percentages: why it is not a “brightness percentage”.

In the VentEurope range, the light sensor is used in fans with the SHT option. In the option insert, you will find four sensor setting options: 50%, 70%, 90%, or off. These numbers represent sensitivity levels, not the percentage of brightness.

The 50%, 70%, and 90% switches indicate the sensor’s sensitivity to light brightness:

• 50% — reacts to moderate ambient lighting. Often sufficient for soft lighting fixtures and mirror lights.
• 70% — reliable activation with standard bathroom lighting when the main ceiling light is turned on.
• 90% — requires bright lighting and will usually ignore low ambient light and decorative lighting.

In real life, a bathroom where it is comfortable to shave or apply makeup is typically around 60–100 Lux. Lux is the unit that measures how much light actually falls on a specific surface.

What determines whether there is enough light for a “trigger”?

1. Source brightness (Lumens). A 1000 Lm lamp is objectively more powerful than a 600 Lm lamp, but what matters is how much of that light actually reaches the sensor.
2. Light direction. The sensor’s sensitivity depends on the angle at which light falls on it. Light that strikes at a sharp angle is detected less effectively. Deep shades, frosted diffusers, or directional spotlights can reduce the amount of light reaching the sensor.
3. Distance. The farther the light source is from the sensor, the lower the brightness level reaching it.
4. Angle of incidence. If the sensor is turned sideways, its sensitivity decreases. If it faces the light source directly, it detects light more effectively.
5. Reflections. White ceilings and light-colored tiles reflect light, while dark surfaces absorb it.
6. Transparency and cleanliness. Deep or frosted shades reduce the light flux, and a dusty sensor window can also lower sensitivity.

A lumen is the total amount of light emitted by a source in all directions.

Real-life examples: why the light trigger is sometimes insufficient.

• Soft ceiling light (around 600 Lm). The sensor receives a moderate brightness level. This is often enough for the 50% sensitivity setting. For 70%, it may be borderline depending on the shade and distance.
• Bright downlight (around 1000 Lm). Reliable activation at the 70% sensitivity level and sometimes even at 90% in a typical bathroom.
• Spotlights not directed at the sensor. The room may be bright, but the sensor remains in shadow if the light is directed toward a wall or mirror rather than the sensor itself.

The main thing to remember.

How it looks in practice:

• 50% — soft lighting. A single ceiling lamp with a frosted shade, night lighting, or mirror illumination. The sensor is not directly facing the light source.
• 70% — normal lighting. The main ceiling light provides even illumination without deep shadows. The sensor can detect the source directly or through reflections.
• 90% — bright mode. Requires strong lighting to activate. Useful when you want to ignore weak daylight or decorative lighting.

Finally, let us answer some frequently asked questions.

Is this related to the lamp’s wattage?

No. Watts represent power consumption. The sensor responds only to the brightness of the light falling on it. Two lamps with the same wattage may produce very different levels of illumination.

Why are the percentages not equal to “50% brightness”?

Because they represent sensitivity levels. At the 50% setting, the sensor more easily detects that the environment is bright. At the 90% setting, it requires much stronger illumination.

Does the size of the sensor matter?

No. What matters is the brightness level reaching the sensor, not its physical size.

Does color temperature affect it?

If the brightness level is the same, warm and cool light will trigger the sensor in the same way because it responds to the visible light spectrum.