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# UnitIlluminance

A unit of measure for illuminance.

```
class UnitIlluminance
```

## Overview

You typically use instances of [`UnitIlluminance`](/documentation/Foundation/UnitIlluminance) to represent specific quantities of illuminance using the [`NSMeasurement`](/documentation/Foundation/NSMeasurement) class.

### Illuminance

Illuminance is the luminous flux incident on a surface. The SI unit for illuminance is the lux (lx), which is derived as one lumen per square meter (1lm / 1m2).

The [`UnitIlluminance`](/documentation/Foundation/UnitIlluminance) class defines its [`baseUnit()`](/documentation/Foundation/Dimension/baseUnit()) as [`lux`](/documentation/Foundation/UnitIlluminance/lux).

|Name|Method                                                                     |Symbol|
|----|---------------------------------------------------------------------------|------|
|Lux |``doc://com.apple.foundation/documentation/Foundation/UnitIlluminance/lux``|lx    |

## Topics

### Accessing the Base Unit

[`+  baseUnit`](/documentation/Foundation/Dimension/baseUnit())

Returns the base unit.

### Accesing Predefined Units

[`lux`](/documentation/Foundation/UnitIlluminance/lux)

The lux unit of illuminance.

## Relationships

### Inherits From

[`Dimension`](/documentation/Foundation/Dimension)

### Conforms To

[`Hashable`](/documentation/Swift/Hashable)

[`NSSecureCoding`](/documentation/Foundation/NSSecureCoding)

[`Sendable`](/documentation/Swift/Sendable)

[`CustomDebugStringConvertible`](/documentation/Swift/CustomDebugStringConvertible)

[`SendableMetatype`](/documentation/Swift/SendableMetatype)

[`CustomStringConvertible`](/documentation/Swift/CustomStringConvertible)

[`Equatable`](/documentation/Swift/Equatable)

[`CVarArg`](/documentation/Swift/CVarArg)

[`NSObjectProtocol`](/documentation/ObjectiveC/NSObjectProtocol)

[`NSCoding`](/documentation/Foundation/NSCoding)

[`NSCopying`](/documentation/Foundation/NSCopying)

---

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