Lighting

Lighting is vital for a colony. A colony will have a limited number of windows, so artificial lighting may be required at all times. Plants in greenhouses will probably need to be lit artificially to supplement natural light. Rovers must have headlamps for driving at night or during dust storms.

Types of lighting

Incandescent

Most light bulbs on Earth were incandescent until recently. Due to their relatively low efficiency, incandescent lights are being phased out all over the world. In most commercial installation incandescent light bulbs have been replaced by fluorescents, that are themselves being replaced by LEDs.

Incandescence is a term usually reserved for a solid that emits light as it is heated. In an incandescent light-bulb a metal filament (Usually tungsten, but carbon has also been used in the past,) is heated to around 3000C. A glass or quartz bulb is fitted around the filament and the air evacuated or replaced by an inert gas, because the filament would otherwise oxidize and burn.

Halogen

Halogen light are a variation on incandescent lights, where the filament can last longer due to chemical interactions between the tungsten element and the halogen gas in the bulb.

Fluorescent

Fluorescent lights use a phosphorous coating inside the lamp tube to transform the ultraviolet light emitted by an ionised plasma in the tube into visible light.

Light Emitting Diode (LED)

LED are energy efficient, and produce little heat compared to incandescent, fluorescent, and halogen lights. They use the light emitted from a semi conductor in visible wavelengths and combine red green and blue components to produce white light.

LEDs in 2019 can produce about 220 lumens per watt, while incandescent light bulbs produce only about 14 lumens per watt and fluorescents 80 lumens per watt.

Human response to light

Humans have two types of vision, color and low-light. Once the vision has adjusted to low light, the average human is able to function well in the light of the full moon, but without the ability to see in color.

Health

The proper wavelengths of light are needed by humans to produce Vitamin D. On Earth, about 15 minutes under the noon sun, 3 times a week, is enough to produce the required vitamin D. On Mars, the exposure time would need to be longer. Most type of glass screen ultraviolet light, so exposure under glass would not produce vitamin D. Using ultraviolet light from artificial sources would product the same effect as the sun.

Certain lights, emulating natural sunlight, are used to treat Seasonal Affective Disorder.

Uses

Illumination

The primary use of lighting is illumination of a settlement. A well-lit environment is vital for the morale and safety of the residents. See table below for standard lighting levels.

Agriculture

Many plants require more sunlight than is available on the Martian surface. Dust storms can also obscure the sun for months at a time. Artificial lighting is needed to at least augment the natural light.

Interior grow rooms use artificial light for plant production. This technology was developed for the production of Cannabis in closed environments but is applicable to all indoor grown plants. The most common power used for these installations is 300-600 W/m2 of lighting, or about one quarter to one half the power of full sunlight.

Food production is a factor of the amount of illumination received by the plant. A useful equation for a surface greenhouse is:

Edible food=0.77 x PAR x T-6.1 (reference needed) where:

Edible food= Amount of edible plant mass produced (g/m2/day)

PAR= lighting level of photosynthetically active radiation. On Mars for natural lighting it is 20.8 (mol/m2/day).

T= transmittance of greenhouse surface.

For a greenhouse with a transmittance of 0,8, food production might be (.77 x 20.8 x .8)-6.1 = 6.7 g/m2/day

For 260 days of production per year the yield would be 1.7 kg/m2 per year, or about 17 t/ha.

This can be compared to the crop yields obtained on Earth, that vary between 20 and 100 t/ha for high yield crops. So although Mars surface greenhouses can work, the yield might be relatively low and supplemental lighting required for higher crop yields.

Lighting levels

Common outdoor light levels

Condition	Illumination		Power intensity
	ftcd	lux	W/m2 (W/ft2)
Sunlight	10000	107 527	1300 (120)
Full daylight	1000	10 752	130 (12)
Overcast day	100	1 075	13-18 (1,3-1,8)
Very dark day	10	107
Twilight	1	10,8
Deep twilight	0,1	1,1
Full Moon	0,01	0,11
Quarter moon	0,001	0,011
Starlight	0,0001	0,0011
Overcast night	0,00001	0,00011

The table below provides recommended light levels from the IESNA Lighting Handbook and LPD levels from the IECC 2015

ROOM TYPE	LIGHT LEVEL (FOOT CANDLES)	LIGHT LEVEL (LUX)	IECC 2015 LIGHTING POWER DENSITY Watts/m2 (WATTS PER SF)
Bedroom - Dormitory	20-30 FC	200-300 lux	4 (0.38)
Cafeteria - Eating	20-30 FC	200-300 lux	7 (0.65)
Classroom - General	30-50 FC	300-500 lux	13 (1.24)
Conference Room	30-50 FC	300-500 lux	13 (1.23)
Corridor	5-10 FC	50-100 lux	7 (0.66)
Exhibit Space	30-50 FC	300-500 lux	16 (1.45)
Gymnasium - Exercise / Workout	20-30 FC	200-300 lux	7,8 (0.72)
Gymnasium - Sports / Games	30-50 FC	300-500 lux	13 (1.20)
Kitchen / Food Prep	30-75 FC	300-750 lux	13 (1.21)
Laboratory (Classroom)	50-75 FC	500-750 lux	16 (1.43)
Laboratory (Professional)	75-120 FC	750-1200 lux	19 (1.81)
Library - Stacks	20-50 FC	200-500 lux	18 (1.71)
Library - Reading / Studying	30-50 FC	300-500 lux	11 (1.06)
Loading Dock	10-30 FC	100-300 lux	5 (0.47)
Lobby - Office/General	20-30 FC	200-300 lux	10 (0.90)
Locker Room	10-30 FC	100-300 lux	8 (0.75)
Lounge / Breakroom	10-30 FC	100-300 lux	8 (0.73)
Mechanical / Electrical Room	20-50 FC	200-500 lux	10 (0.95)
Office - Open	30-50 FC	300-500 lux	11 (0.98)
Office - Private / Closed	30-50 FC	300-500 lux	12 (1.11)
Parking - Interior	5-10 FC	50-100 lux	2 (0.19)
Restroom / Toilet	10-30 FC	100-300 lux	11 (0.98)
Retail Sales	20-50 FC	200-500 lux	17 (1.59)
Stairway	5-10 FC	50-100 lux	8 (0.69)
Storage Room - General	5-20 FC	50-200 lux	7 (0.63)
Workshop	30-75 FC	300-750 lux	17 (1.59)