Illumination and visual feeling

Hi everybody,

I am working on a project which tries to control illumination by controling the electrical power consumed by an electrical lamp (a form of dimmer). In a part of this project I need to discuss the relation between the change in the illumination with what the visual system senses. I know that there is a logarithmic relation in sound where dB is used to express the way our auditory system operate and feel but does a similar relation applies to visual system or is there any relation or curve relating the change in the illumination to the effect it has on the visual feeling. Many thanks for your help.

Khashayar

Reply to
khy
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Crossposting to sci.engr.lighting

Reply to
operator jay

Yes, there is a non-linear relationship between apparent brightness (what the human eye/brain system senses) and illuminance (the actual amount of light as measured by a meter.) According to the IES Handbook, 9th Edition the relationship is:

B = a x L^0.33 where B is brightness, L is illuminance and a is a constant. However, there are many other measures of visual perception in addition to brightness, such as the ability to see small objects. Others in this group can discuss these and the brightness/illuminance relationship better than I can.

Reply to
Victor Roberts

There is indeed a curve. It is logarithmic; but the relationships are somewhat more complicated than the one for sound.

A good explanation is in the IESNA Handbook (9th. Edition), Page 3-24 and especially Fig. 3-37. which shows plots of Relative Visual Performance vs. Task Contrast and retinal illuminance. That's probably more than you need for your project, though.

Do a Google on "dimmer curve" and you'll find some practical information; but the curve is sensitive to the type of light source since the dimming characteristics of incandescent and discharge lamps are quite different.

Terry McGowan

Reply to
TKM

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