Introduction to Illumination Concepts

The ratio of reflected light to incident light on a surface.

An angle formed by the surface passing a point and the periphery of an area.

The unit for measuring solid angle.

The illumination of a surface is inversely proportional to the square of its distance from a point light source.

The amount of light falling on a surface per unit area.

A light source that can be considered as a single point for calculating illumination.

The bouncing of light off a surface.

The light falling on a surface.

Tungsten vapor in high-vacuum bulbs collects at the top, causing a dark spot.

Chemicals that reduce tungsten vapor to prevent blackening in incandescent bulbs.

Vacuum lamps are used for low wattage (up to 40 watts) because heat loss from gas is greater than in higher wattage lamps

Halogen vapor reacts with evaporated tungsten to bring it back to filament.

Halogen lamps offer higher luminous efficiency (22-33 lumens/watt) compared to incandescent.

Using gas and voltage to create illumination through ionization.

After ionization begins in gas, current tends to increase, and resistance falls in a gaseous discharge lamp.

Used in gaseous discharge lamps to limit and control current and provide initial ignition voltage

Lumens output is proportionally related to voltage raised to the power of 3.55 (lumens output ∝ V³.⁵⁵).

The diameter of a tungsten lamp filament can be as small as 10 microns, depending on the voltage and wattage.

Lamps filled with inert gas (e.g., argon) alongside a small amount of nitrogen to improve efficiency and reduce arcing, dealing with high operating temperatures.

Calculated as I²R (current squared times resistance), where resistance relates to material property and length.

Given by eK * surface area * (T¹⁴ - T₀⁴), where T₁ is filament temperature, and T₀ is the surrounding medium temperature.

Proportional to voltage squared (Luminous efficiency ∝ V²).

Lamp life is inversely proportional to voltage raised to the power of 13 (life ∝ V⁻¹³).

Lamp life is inversely proportional to voltage raised to the power of 14 (life ∝ V⁻¹⁴).

Contain circuits with rectifiers, a capacitor, and transistors to create a high-frequency AC-to-DC inverter, which powers the lamp tube.

About 10,000 hours (lamp), 50,000 hours (ballast).

Consumes 20-30% less energy than incandescent lamps for the same light output.

60-72 lumens per watt.

More energy to manufacture CFLs, though offset by their longer life & lower energy use.

3-10 times higher than an equivalent incandescent lamp.

Takes several seconds to reach full brightness.

Frequent on/off cycles shorten CFL lifespan.

Sodium vapor lamps operate on alternating current (AC) and need a choke to control current.

Initially, a sodium vapor lamp emits a red-orange glow from neon gas before vaporizing and ionizing sodium to produce yellow light.

Sodium vapor lamps have a low power factor (around 0.3), and a capacitor is needed to improve it to (around) 0.8.

High-pressure mercury vapor lamps have an inner bulb containing mercury and argon, enclosed in another outer glass bulb.

The lamp initially discharges through argon, which allows the mercury vaporization process and emission of bluish-green light to commence.

High-pressure mercury vapor lamps take about 4-5 minutes to reach full brightness.

Sodium vapor lamps have an efficiency of about 40-50 lumens per watt.

High-pressure mercury vapor lamps have an efficiency of about 30-40 lumens per watt.

A lighting scheme where over 90% of light directly illuminates the work surface. It's efficient but creates hard shadows and glare.

60-90% of light is directed downwards (to the work plane) with the rest illuminating the walls and ceiling. Good for rooms with high ceilings, reducing glare with diffusers.

60-90% of light is reflected off the ceiling, while some reaches the working plane, resulting in softer shadows and no glare.

Light is reflected off the ceiling (using inverted/bowl reflectors), producing a soft, diffused light with minimal glare. Perfect for decorative purposes.

Uses lamps with diffusing glass, providing nearly uniform illumination in all directions.

Sharp, distinct shadows.

Excessive brightness that can create discomfort.

Light scattered in many directions, resulting in softer light.