Principles of Physiologically Adequate Lighting & Measurement

Posted on Sep 4, 2024 in Other subjects

Principles of Physiologically Adequate Lighting & Measurement

Visible Light

Visible light spectrum: 500/600-700/800 nm

Types of Inadequate Lighting

Insufficient Light

Not enough light for the visual task.

Glare

Too much light for the need. Occurs when a bright light source or reflection interferes with object visibility.

Causes of Reflected Glare:
  • Light reflected from polished, shiny, or glossy surfaces
  • Glass on picture frames or windows at night
  • Monitors/screens
Causes of Direct Glare:
  • Very bright light from poorly positioned light fixtures
  • Sunlight

Improper Contrast

Two types:

  1. Uneven Light Levels: Very different light levels from one area to another. If the surrounding area is brighter than the work area, attention is drawn away from the task.
  2. Low Color Contrast: Too little contrast between print and paper, making reading difficult.

Other Issues:

  • Poorly distributed light
  • Flicker

Consequences of Inadequate Lighting

  • Safety Hazard: Misjudgment of the position, shape, or speed of an object can lead to accidents and injury.
  • Reduced Work Quality and Productivity: Affects the quality of work, specifically in situations where precision is required.
  • Health Hazard: Too much or too little light strains eyes and may cause eye discomfort (burning, etc.) and headaches.

Factors Influencing Light Requirements

  • Type of Task: The more detailed the task, the greater the light requirement (e.g., process control room – 300 lux, corridor – 50 lux, studying room – 750 lux).
  • Surface Properties: Whether surfaces reflect or absorb light (e.g., display screens can cause glare).
  • General Work Area: To reach proper light levels and uniform distribution, many light fixtures are designed to reflect light off walls, ceilings, and objects.
  • Individual Vision: Visual acuity varies between individuals.
  • Light Color: All sources of light have a particular color which can make text and diagrams difficult to read.

Measuring Light in Lux

The amount of light falling on a surface is measured in units called lux.

Recommended Lux Levels:

  • Adequate general lighting is usually between 500 and 1000 lux when measured 76 cm (30 inches) above the floor.
  • Public spaces with dark surroundings: 20-50 lux
  • Working spaces where visual tasks are only occasionally performed: 100-200 lux
  • Performance of visual tasks of high contrast or large scale: 200-500 lux
  • Performance of visual tasks of medium contrast or small size: 500-1000 lux
  • Performance of very prolonged and exacting visual tasks: 5000-10000 lux

Measuring and Evaluating Light

  • Measure the average illumination throughout the workplace.
  • Compare measurements to the recommended levels.
  • Look for shadows, especially over work areas and on stairways.
  • Ask workers if they suffer from eye strain or squint to see.
  • Workers should sit in their normal working positions during measurement to give accurate results.

Correcting Insufficient Light

  • Replace bulbs on a regular schedule. Old bulbs give less light than new ones.
  • Clean light fixtures regularly. Dirt reduces the amount of light emitted.
  • Add more light fixtures in appropriate places.
  • Paint walls and ceilings light colors to reflect light.
  • Use more reflected light and local lighting to eliminate shadows.
  • Do not position workstations with light fixtures directly behind the worker.

Daytime Illumination Measurement

  • Depends on various factors:
  • Time of day and year
  • Weather
  • Size and number of windows and their facing direction
  • Colors of the walls, ceiling, furniture, curtains, etc.
  • Barriers in front of the windows

Assessment:

In the winter months at midday ±2h with a diffusely overcast sky (≤5000 lx outdoor), two people wearing black simultaneously measure the intensity of illumination inside and outside.

Artificial Illumination Measurement

  • Take many readings inside and calculate the average.
  • Assess evenness as a relation of illumination min./illumination max.
  • Compare results with standard requirements (e.g., lecture hall – 400-500 lux).

Consequences of Inadequate Lighting (Summary)

  • Myopia
  • Neurotic complaints
  • Ocular complaints
  • Decreased work quality/quantity
  • Increased injury rate