Visual comfort system is most common evaluation in the USA/Canada. This is expressed as percentage of people considering an installation comfortable as viewed from one end. Glare tables list various proportions and layout of room for glare free lighting. Figure of merit is based on a source of 1000 lm.from a luminaire. If VCP ≈ 70% then the system is said to be glare free. British method employs Zone of luminaire with a classification for quality of light expressed as Glare index. Luminance limit system is adopted in Australia. Standard code for Luminaire base lamp. dep. on room dimensions, mounting height and a Empirical shielding angle
Luminance curve system is employed in Europe.
Luminance limits for luminaires critical angles, γ are 45º < γ < 85º. Quality class is expressed from A to E type is based on Luminaire orientation.
Type 1. Luminous sides when Luminous side plane> 30 mm
General light is predominantly light coming downwards. Typically reflectance of 0.5 for walls /ceiling and 0.25 for furniture. How is Glare evaluated?
1. Determine luminance of the source between 45º - 85º
2. Determine the quality class and illuminance required.
3. Select the curve – class / level.
4. Determine. Max. Angle to be considered from length & height and plane of eye level & plane of luminaires. (Refer to Fig 1)
5. Horizontal limit based on” a / h”, part of the line (or curve) to be ignored.
6. Compare luminance of one luminaire with selected part of the limiting curve.