Brightness of products

Published on 8 August 2022 at 12:02

Indirect illumination is mostly used for ambient illumination to create mood. The light source is mostly invisible and illuminates surfaces. The illumination of the surface from the top or side highlights the structure in a decent way. Because we reflect light on a surface the perceived brightness diminishes with the reflection behaviour of this surface.  In comparison a direct illumination is when you directly see the last surface of the light system, usually a diffuse plastic element. This element covers the surface, give a haptic end user experience, hides the technology and fixation elements that could be perceived as brightness spots. Direct visible light lines and areas are usually brighter than indirect ones because the light system is more efficient. For this the ambient illumination is mostly used to be seen in darker environment conditions while the direct illumination can be seen during daylight. With high power LED or LED stripes the ambient illumination can become functional as well to create warnings or display the product state.

Perceived brightness as Luminance values

How high do you need to go so the light is seen during different conditions. Here is a practical guide for the luminance/brightness that you should have so the light can be seen well. Luminance in cd/m² can be measured and compared to the following values.

Ambient illumination

In darkness: product illumination 0,1-10 [cd/m²] 

In twilight: product illumination 10-50 [cd/m²]

Daylight

Cloudy day: product illumination 200-400 [cd/m²]

Normal daylight:  product illumination 400-600 [cd/m²]

Daylight with sunshine: product illumination 600-1200 [cd/m²]

If the light in your product should be seen under strong summer sunshine the luminance has to go higher than 3500cd/m²

The higher the brightness the more useful is the application for functional purposes and warning. But with very high brightness the product needs more LED, more LED power and in case its used in darkness is probably too bright to watch for the user. Be aware of the use case and specify what you need. 

Video shows how the perceived brightness changes under sunshine vs room illumination. Center picture shows ambient light in piano to highlight the wood relief surface. And the right picture shows a direct light line integrated in a front panel and the light system to create this light line.


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