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Lighting Fundamentals

How to: Understand Lighting for People and Plants.

Inda-Gro logoHuman and Plants use distinctly different wavelengths within the sunlight spectrum. Studies have proven that plants receive some benefit with a small amount of light of the human wave spectrum but the vast majority of plant needs come from the Ultraviolet (down to 380 nanometers) and Infrared (up to 720 nm) range of the light spectrum. Plants absorb more Red, Deep Red, Blue and Deep Blue than we humans use for our vision.


par-graph.jpg

How Plants Absorb Light:

For plant lighting, higher lamp efficiencies, within the proper spectrums, means less operating costs by lowered wattages, lower heat generation by the lamp/ballast, maximum canopy penetration, long lamp life and minimum lumen depreciation will all contribute to succesful grows.





human-eye-response.graph.jpgHow People See Light: 

For human vison we design lighting levels with two distinct kinds of lumen output. The first is called Photopic or Design Lumens, which represents the relative sensitivity of the eye under intense lighting such as daytime cloudless outdoor sun conditions. Photopic lumen output is registered by the cones in the human eye and is measured in Lumen, Lux and Foot Candles.

The second type of lumens are called Scotopic, which represent the sensitivity of the eye under typical interior or night lighting conditions and cannot be measured directly with a standard light meter. Scotopic lumen output is registered by the rods of the human eye and also controls pupil size directly effecting visual acuity for given task levels.

plant light absorption


Measuring Light, Energy and Efficiencies

Below we show how different light sources Design Lumen readings compare when read by a standard light meter and measured in Conventional Photopic Lumen values.

For lighting design that wishes to maximize energy efficiencies by specifying light sources with both high Scotopic and Photopic Lumens, a Correction Factor (S&P Ratio) must be applied to the Photopic Lumen per Watt readings.

When applying this correction factor you will notice drastically different usable light outputs as measured in Pupil Lumen per Watt. Higher Pupil Lumens per Watt will significantly reduce the amount of energy necessary to satisfy maximum visual acuity within the optimal yellow-green regions of the spectrum. In other words; the higher the Pupil Lumen/Watt the less energy will be required of the lamp for the eye to accurately see what it's observing.

To illustrate this you can see by the charts below that the LPS (Ugly Yellow Street Lighting) lamp is more efficient from a conventional efficacy (Lm/W) perspective. However the LPS has a very low S/P ratio and poorpupil lumens per watt when compared to induction. Now the CRI and the VEL would indicate poor visual acuity. What this means is that while there may be a high lumen per watt when using LPS, the ability to accurately gauge the color of what we are observing is extremely poor.

Measuring Energy Efficiency Design Lumens

LAMP TYPE

Conventional Lumens
per Watt

Correction Factor
(S&P Ratio)

Pupil Lumens
per Watt

Induction Lamp (5000K)

85 1.96 166.6
Metal Halide 815 1.49 126
Warm White Fluorescent (2900K) 65 0.98 64
Low-Pressure Sodium 165 0.38 63
High Pressure Sodium (50W) 65 0.76 49
LED (5000K) 20 2 40
Delux Mercury Vapor 40 0.86 34
Tungsten Halogen 22 1.32 29
Standard Incandescent 15 1.26

1

  

Induction Lamps: Why They Appear Brighter:

Below we show how Photopic and Scotopic Values vary between different lamp types and how bright they will then appear to the eye. This is known as Apparent Brightness and is not measured in the conventional Lumens, Lux or Footcandle readings.

There are a number of terms engineers use that reference Apparent Brightness; Visually Effective Lumens (VEL), Spectrally Effective Lumens (SEL) or Pupil Lumens as this measurement, but whatever phrase you use, they all refer to the same thing:

Apparent Brightness
Type

Wattage

Photopic
Value
Scotpic
Value
VEL
Induction 100 Watt 9,625 19,250  16,527
"" 200 Watt 20,500 41,000  35,201
"" 250 Watt 27,200
54,400 46,706 
"" 400 Watt 54,090 108,180 92,883
High Pressure Sodium 150 Watt 11,250 8,550 9,082
"" 250 Watt 22,100 16,796 17,841
"" 400 Watt 36,000 27,360 29,063
"" 1000 Watt 90,000 68,400 72,630
Metal Halide (Pulse Start) 150 Watt 8,000 11,920 10,919
"" 250 Watt 15,000 22,350 20,473
"" 400 Watt 28,000 41,720 38,216
"" 1000 Watt 93,000 138,570 126,940










 

Standard Units of Measurement for Vision:

When taking into account the standard photometric measurements of light for human vision the system of units we measure would be the LUMEN which measures the total amount of light emitted from a light source.

This light is then distributed over an area and the illuminated area is measured in LUX. LUX is measurement of intensity as percieved by the human eye. It is a way of measuring how many LUMENS fall within a square meter of an illuminated surface.

The difference between the LUX and the LUMEN is that a LUX measures the area over which the LUMEN is distributed. These levels are inversely proportional to the area being lit. The larger the area the lower the intesity of the LUX levels. For example a reading of 1000 LUMENS would correlate to 1000 LUX at a 1 meter area however the LUX illumination levels would fall to 100 LUX over a 10 meter area.

In the United States you'll often hear light measurements in FOOTCANDLES. This term is used alot in construction related projects and by engineers who deal with US Standards of measurement. LUX and FOOTCANDLES are different units of the same quantity in that FOOTCANDLE will measure the amount of LUMEN PER SQUARE FOOT whereas LUX measures the LUMENS PER SQUARE METER. Other then in the United States you will not usually hear light measured in FOOTCANDLES.

Since all light is emitted in wavelengths, and we know that the human eye can see certain wavelengths better then others, with the peak being measured @ 555 nanometers, we can now determine a given lamps source LUMENS PER WATT.

The LPW measurement adjusts for the spectral wavelengths the lamp produces. So when determining a task level of illumination for human eyesight, we can decide which lamp will best suit the task for the least amount of wattage, with factored depreciation, and how important the color, as measured in the CRI, to best match the task.

Operational Comparisions
Activity Inda-Gro 
Induction
LPS HPS MH T8 LED
Lifespan (hrs.)

60-100K

16-18K

 18-24K

8-10K

6-10K  

30-50K 

Power Consumption

 LOW

 HIGH

 HIGH

 LOW

 LOW

 LOW

Maintenance Cost

VERY LOW 

HIGH 

HIGH 

HIGH 

HIGH 

LOW 

 Average Mercury Content

5mg

6-45mg

 12-50mg

10-100mg

10-43mg

N/A

CRI

85

N/A

21

64

62

75

Color Temperature

2700-6500K

1800K

2700K

3000 - 4000K

3000 - 5000K 

2700 - 6500K

S/P Ratio*

1.96

0.38

0.76

1.49

1.62

1.85

Mean Lumen
per Watt

65-90L/W 

 183-200L/W

 150L/W

 65-115L/W

 80-100L/W

50-100L/W 

Lumen Maintenance 

70% 

80-85% 

 55-65%

 55-60%

 50-75%

45-60% 

 Ignition time

Instant

6-8 minutes 

5-8 minutes

5-10 minutes 

instant

instant 

 Hot Re-strike

 YES

 NO

 NO

NO 

YES 

YES 

 Flicker

 NO

 YES

  YES

  YES

  YES

NO

The         more

you

learn 

 the

 less

you 

need!




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