How Bright is That Light?

HOW BRIGHT IS THAT LIGHT? Lumens? Lux? Watts? A simple guide to some of the basics in understanding how brightness and light are measured in modern electric lighting. THINKING IN LUMENS TERMS LUMENS The symbol for lumens is: Im The simplest way to consider how much light power a bulb or other electric light will give off is to look at the lumens. The higher the number, the brighter the bulb. LOOK OUT FOR THE LUMENS TOTAL LUMENS FIGURE HT BULB 300 WHEN BUYING LAMPS OR BULBS WHAT? NOT WATTS A watt is a unit of power, but in relation to a light bulb or other electric light, watts are the power consumed, not the amount of light given off. Thinking in watts worked in the past because most light bulbs were incandescent which emitted a fairly uniform amount of light for the power consumed. The symbol for watts is: WATTS OF ELECTRICITY ELECTRIC POWER SUPPLY COMPARING LUMENS AND WATTS To show how many lumens you need to look out for, here's how lumens compare to the watts for a standard incandescent bulb. 100w 75w 60w 40w | 1200 800 700 400 12 10.6 11.6 10 LUMENS PER WATT (Im/w) The amount of light given of by the amount of electrical power going in, lumens per watt is a measure of the efficiency of the light. KEEPING AN EYE ON YOUR LUX So how much area will a light cover? That's a job for lux – the unit of luminous flux (or lumens) spread over an area. 1 lux is equal to 1 lumen per square metre. LAMP EMITS 1,000 LUMENS The symbol for lux is: lx 10 M2 = 1 M2 = 10,000 LUX 1,000 LUX -o OOH AH, CANDELAS Candelas (cd) are used to measure the the amount of light emitted in a specified direction. A common candle emits light with a luminous intensity of roughly one candela. The symbol for candelas is: cd HILCLARE LIGHTING MANUFACTURE LIGHTING DESIGN ENERGY MANAGEMENT www.HILCLARE.COM CANDELAS WATTS ΚΚκκακα Tumens M/u|