FACTORS AFFECTING LIGHT LEVEL STANDARDS

FACTORS AFFECTING LIGHT LEVEL STANDARDS

Light level standards are affected by light quantity and quality desired, fixture efficiency and other
applicable factors.

Quantity of light or the light output and light levels is measured in lumens, lux and footcandles.
Initial Lumens/ Footcandles reflect the amount of light produced by a lamp when it is installed.
Supply voltage variations, lamp’s interaction with the ballast and dirt build up (Luminaire Dirt
Depreciation) reduce the produced amount of light. Lessening of light output over time, while
continuing to consume the same energy amounts (Lamp Lumen Depreciation) also reduces the
light levels of the lamp and waists energy.
Maintained Footcandles show the light level after light loss factors are taken into account over a
period of time. Mean Lumens show the average light output over the lamp’s lifetime. When
addressing lighting standards a provision for the light quantity depreciation over time due to
multiple factors should be made.

Quality of light depends on the brightness, distribution and light color.
Photometric brightness (Luminance) is the amount of light leaving the lamp or reflecting from a
surface. It is measured in footlamberts, candelas/sq. ft. and candelas/ square meter (metric).
Brightness can produce levels of glare if not contained properly. Glare that comes directly from the
light source is a Direct glare. Reflected glare occurs on the task surface. Discomfort glare does
not blind but creates discomfort. Disability glare prevents vision and blinds. Every fixture has a
Visual Comfort Probability (VCP) rating that reflects its level of visual comfort.

Glare can severely interfere with visual comfort. High brightness ratios produce high contrast and
can also create a visual fatigue during “transient adaptation”, which is the adaptation process of the
eye when brightness changes.

Light Color depends on the visible light spectrum and the wavelength composition of the lamp light
(Spectral power distribution), the color of the light the lamp produces (Color temperature
measured in Kelvin), the way the light source makes the color appear to human eyes and how well
subtle variations in color shades are revealed (Color rendering -Color Rendering Index from 0-
100). The higher the CRI is, the better the color rendition appears. An inappropriate color rendition
can deceive the eye and supply it with wrong information.