Question 1

How many lumens do I need for my room?

Accepted Answer

The number of lumens you need depends on the room type and activity. Calculate it by multiplying the recommended lux level by your room area in square meters. For example, a general office needs 500 lux, so a 20 m² (215 sq ft) office needs 10,000 lumens total. A living room needs about 200 lux, while a workshop needs 500 lux. Use our Lux to Lumens calculator tab to find the exact number for your space.

Question 2

How do you convert lumens to watts?

Accepted Answer

To convert lumens to watts, divide the lumens by the bulb efficacy (lumens per watt). Different bulb types have different efficacies: LEDs produce about 90 lumens per watt, CFLs about 60 lm/W, halogen about 20 lm/W, and incandescent about 15 lm/W. For example, to produce 800 lumens, an LED uses about 9 watts, a CFL uses 13 watts, while an incandescent uses 60 watts.

Question 3

What LED replaces a 100 watt incandescent bulb?

Accepted Answer

A 100-watt incandescent bulb produces approximately 1,600 lumens. To get the same brightness from an LED, you need a bulb rated at about 15-18 watts. This represents an energy saving of over 80%. Similarly, a 60W incandescent is replaced by a 9W LED, and a 40W incandescent by a 5W LED. Always match lumens (brightness) rather than watts (energy) when choosing replacements.

Question 4

How do you calculate beam spread for a light fixture?

Accepted Answer

Beam spread (diameter) is calculated using the formula: Diameter = 2 × Distance × tan(Beam Angle / 2). For example, a fixture with a 40° beam angle mounted 10 feet above a surface produces a beam diameter of about 7.3 feet, covering approximately 41.6 square feet. Narrow spot lights (10-15°) produce tight focused beams, while wide floods (60-120°) spread light over larger areas.

Question 5

What are foot-candles in lighting?

Accepted Answer

A foot-candle (fc) is a unit of illuminance measuring how much light reaches a surface. One foot-candle equals one lumen per square foot, or approximately 10.764 lux. Foot-candles are commonly used in the United States for lighting design, while lux is the international standard. The IES (Illuminating Engineering Society) publishes recommended foot-candle levels: offices need 50 fc, retail stores 50-75 fc, warehouses 30 fc, and operating rooms 200 fc.

Question 6

How do you convert lux to lumens?

Accepted Answer

To convert lux to lumens, multiply the lux level by the area in square meters: Lumens = Lux × Area (m²). Lux measures illuminance (light hitting a surface) while lumens measure total light output. For example, if you need 500 lux in a 30 m² room, you need 15,000 total lumens. If your area is in square feet, first convert by multiplying by 0.0929 to get square meters.

Question 7

What LED wattage replaces a 400W metal halide fixture?

Accepted Answer

A 400-watt metal halide fixture producing approximately 36,000 lumens can typically be replaced by a 120-150 watt LED fixture. LED replacements for HID fixtures are more efficient because LEDs direct light more precisely with less wasted spill light and have much less lumen depreciation over time. This switch saves roughly 250-280 watts per fixture, which translates to significant energy savings in commercial and industrial applications.

Question 8

What is the IES recommended light level for an office?

Accepted Answer

The IES (Illuminating Engineering Society) recommends 500 lux (approximately 50 foot-candles) for general office spaces. Open plan offices may use 300 lux (30 fc), while task-intensive areas may need up to 750 lux (75 fc). Conference rooms typically require 300 lux. These are maintained light levels, meaning the fixture output should account for light loss over time due to lamp depreciation and dirt accumulation.

Lumens	LED	CFL	Incandescent	Halogen
250 lm	3W	5W	25W	18W
450 lm	5W	8W	40W	29W
800 lm	9W	13W	60W	43W
1,100 lm	13W	18W	75W	53W
1,600 lm	18W	23W	100W	72W
2,600 lm	28W	40W	150W	120W
3,200 lm	35W	50W	200W	150W

Lumens	LED Watts	CFL Watts	Incandescent Watts	Halogen Watts
250 lm	3W	5W	25W	18W
450 lm	5W	8W	40W	29W
800 lm	9W	13W	60W	43W
1,100 lm	13W	18W	75W	53W
1,600 lm	18W	23W	100W	72W
2,600 lm	28W	40W	150W	120W
3,200 lm	35W	50W	200W	150W

HID Type	HID Watts	HID Lumens	LED Replacement Watts
Metal Halide	100W	8,500 lm	30-40W LED
Metal Halide	250W	21,000 lm	70-100W LED
Metal Halide	400W	36,000 lm	120-150W LED
Metal Halide	1000W	100,000 lm	300-400W LED
HPS	150W	15,000 lm	45-65W LED
HPS	250W	28,000 lm	80-120W LED
HPS	400W	50,000 lm	140-175W LED
HPS	1000W	130,000 lm	350-450W LED
Mercury Vapor	175W	7,500 lm	30-50W LED
Mercury Vapor	400W	20,000 lm	80-120W LED

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800 Lumens Equivalent

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Application	Foot-candles	Lux
General Office	50 fc	500 lux
Retail - General	50 fc	500 lux
Retail - Merchandise Display	75 fc	750 lux
Classroom	50 fc	500 lux
Warehouse - General	30 fc	300 lux
Manufacturing - General	30 fc	300 lux
Manufacturing - Detailed	75 fc	750 lux
Assembly - Fine	100 fc	1000 lux
Inspection Area	150 fc	1500 lux
Living Room	20 fc	200 lux
Kitchen - Countertop	50 fc	500 lux
Bedroom	15 fc	150 lux
Bathroom	30 fc	300 lux
Parking Lot	5 fc	50 lux
Hospital - General	30 fc	300 lux
Operating Room	200 fc	2000 lux
Examination Room	50 fc	500 lux

800 Lumens Equivalent

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Foot-candles to Lux Converter

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