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  1. Good lighting is essential for effective vision
    1. Essential factors:
      1. Sufficiency: 15 -20 foot candles is accepted as a basic min for satisfactory vision.
      2. Distribution: uniform having same intensity over whole field of work.
      3. Absence of glare: glare is excessive contrast.
      4. Absence of sharp shadows.
      5. Steadiness
      6. Colour of light
      7. Surroundings: ceilings & roofs should have a reflection factor of 80%, walls 50-60%, furniture 30-40%, floor not >15 – 20 %.
    2. Basic minimum for satisfactory vision: 15-20 foot candles.
    3. DF (day light factor): instantaneous illumination indoors  X  100, Simultaneous illumination outdoors
    4. Measured by modified photo electric meter – Daylight factor meter.
  2. Biologic effects of light: degradation of bilirubin, rhythms of body temp, phy activity, stimulation of melanin synthesis, activation of precursors of vit D, adrenocortical secretion & food consumption.
  3. Recommended illumination

Visual task

Illumination (lux)

Casual reading


General office work


Fine assembly


Very severe task


Watch making


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