All mighty equation!
The equation is about indoor environmental quality (IEQ) composing from indoor air quality (IAQ), indoor thermal quality (ITQ – also known as thermal comfort), indoor lighting quality (ILQ – also known as visual comfort) and indoor sound quality (ISQ – also known as acoustic comfort). Read more about IAQ and ITQ (links below).
ILQ is the indoor lighting quality!
Visual comfort or Light has a significant impact on health and well-being including many bodily functions, i.e. physiology bodily functions, etc. Variations of lighting (intensity, light levels, distribution, ambient lighting and color of light) can stimulate people´s alertness and mood.
There are certain treshold values for visual comfort parameters, for example, the illuminance of the bedroom should be at least 100 lux, the office 300 lux and conference rooms 500 lux, etc. Illuminance is measured using a grid (with a certain length of the area, distance points and the number of grid points).
Typically it is measured as baseline and post-installation (with no daylight, typically after sunset). Adjacent electric lighting is switched off and potential temporary obstructions are removed.
ISQ is the indoor sound quality!
Sound is a pressure fluctuation in the air. In general, the greater the amplitude of the pressure fluctuation, the “louder” the sound will be perceived by people. Loudness is a subjective measure describing and sound pressure level is an objective measure, describing acoustic comfort. The sound can maybe a combination of background noise and single or several other sources.
The threshold values for acoustical parameters include noise criteria (typically between 30-50 dB), reverberation time (below 0.1-0.8 m/s) and speech transmission index. It all depends on the type of space, for example between two offices 38 dB, between the toilet and other sensitive spaces 38 dB and public space 40 dB, etc.
There are various types of equipment and different limitations to the testing of the sound. All is described in respective standards.