The International System of Units (SI), commonly known as the metric system, is the international standard for measurement. The SI plays an essential role in international commerce and is commonly used in scientific and technological research and development. This cache is part of the SI geoart that allows you to learn about the SI units. Visit the introduction cache to learn more about this geoart.
Luminous intensity: candela (cd)
The candela is the SI base unit of luminous intensity. It measures the luminous power per unit solid angle emitted by a point light source in a particular direction.
A common wax candle emits light with a luminous intensity of roughly one candela.
Luminous flux: lumen (lm)
The lumen is the SI derived unit of luminous flux. It measures the total quantity of visible light emitted by a source in all directions. It represents the “amount” of visible light present.
1 lm = 1 cd ⋅ sr
If our wax candle can uniformly radiates visible light in all directions, it has a total luminous flux of 1 cd × 4π sr = 12.57 lumens.
Illuminance: lux (lx)
The lux is the SI derived unit of illuminance. It measures luminous flux per area. It represents the intensity of illumination on a surface.
1 lx = 1 lm / 1 m2
If we place our wax candle 0.3 metres away, we’ll see an illuminance of about 10 lux.
On a sunny day, the illuminance on earth surface is between 10000 and 25000 lux, when measured away from direct sunlight. However, during a solar eclipse, some of the sunlight is blocked by the moon, resulting in reduced illuminance on the earth surface. This can be measured with a LUX meter.
This Geocache
When you’re shopping for lightbulbs, compare lumens to be sure you’re getting the amount of light, or level of brightness, you want. How many lumens do you need to replace a 75 watt incandescent bulb? Subtract 101 from this number to get ABC.
The same light bulb illuminates an area at 2.12 lux. How large is the surface area in square metres? Round to an integer to get DEF.
Final coordinates: N 39° 08.ABC W 077° 08.DEF
You can validate your puzzle solution with certitude.
Cache container is a baby-nano with tiny log sheet. A pair of tweezers is mandatory for log retrieval. To conserve space, please omit the date and write the first two letters of your username only.
Some hides are located along a road without sidewalk. For your safety, please walk on the grass out of the car lanes, and avoid going at night without wearing a safety vest.
Lists of Caches in SI geoart
- introduction
- second and hertz
- metre
- kilogram
- m/s and km/h
- mole
- radian and steradian
- m/s² and newton
- m² and pascal
- joule and watt
- ampere and coulomb
- volt and farad
- ohm
- kelvin
- candela, lumen, and lux
- bushel
- foreword & afterword
- prize distribution