What is light decay?

Light decay refers to the gradual reduction in brightness or intensity of light as it travels over a distance or as the light source ages. This phenomenon is commonly observed in both natural and artificial lighting. The concept can be understood in different contexts:

1. Distance-Based Light Decay (Inverse Square Law)

• Physical Principle: In the context of physics, light decay often follows the inverse square law, which states that as light travels away from a source, its intensity decreases by the square of the distance from the source. For example, if you double the distance between a light source and the surface it illuminates, the light intensity will be reduced to a quarter of its original value.
• Impact on Lighting: This means that the farther the light source is from an object or surface, the less effective the light will be in illuminating it. This is important for planning lighting in spaces like rooms, outdoor areas, or photography setups.

2. Light Decay in LEDs and Light Bulbs

• Aging of Light Sources: Light decay can also refer to the decrease in brightness over time as a light bulb or LED ages. Over the course of its lifespan, a light bulb will gradually lose its ability to emit the same intensity of light it did when it was new.
• LEDs: For LEDs, this is typically called lumen depreciation, where LEDs lose their brightness slowly over thousands of hours. Even though LEDs last longer than incandescent bulbs, they do experience some degree of light decay.
• Incandescent and Fluorescent Bulbs: Incandescent bulbs tend to burn out gradually, while fluorescent lights lose brightness more rapidly, especially if they are frequently turned on and off.

3. Light Decay in Photography and Cinematography

• In photography, light decay refers to the diminishing of light as it moves from the light source to the subject. This is a consideration in lighting setups, where light modifiers and reflectors are used to manage light intensity and distribute it more evenly.

4. Atmospheric Light Decay

• Natural Decay: In nature, light decay can also occur due to atmospheric conditions. For example, light from the sun or streetlights will lose some intensity as it passes through fog, dust, or other particles in the air. This type of decay is more noticeable in outdoor environments.

Conclusion:

Light decay is a natural occurrence that can affect the efficiency of lighting, both in terms of distance and the aging of light sources. Whether you're dealing with the positioning of lights in a room or the longevity of your light bulbs, understanding light decay can help you better plan your lighting setup to ensure optimal performance and ambiance.