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Lighting 101 |
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| Lamp Family |
Source
Type |
Efficacy
(lm/W) |
Lamp
Life
(rated hours) |
LLD |
CRI
Sensitive |
Temperature | |
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| Induction Lamps |
Area |
85 |
100,000 |
75% |
80 |
N |
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| Halogen
Incandescent |
Point |
20 |
3,000 |
100% |
100 |
N |
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| Fluorescent |
Linear |
95 |
25,000 |
95% |
86 |
Y |
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| Compact
Fluorescent |
Area |
70 |
12,000 |
86% |
86 |
Y |
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| Pulse
StartMetal Halide |
Point |
100 |
20,000 |
85% |
70 |
N |
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| Ceramic
Metal Halide |
Point |
90 |
20,000 |
85% |
92 |
N |
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| High
Pressure Sodium |
Point |
110 |
24,000 |
90% |
21 |
N |
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| Incandescent |
Point |
85 |
1,000 |
95% |
100 |
N |
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| White
LEDS |
Projection |
45 |
50,000 |
70% |
75 |
Y | | |
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| Color Rendering Index
(CRI) | |
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A Color Rendering Index
provides a means of comparing the effect a light
source has on the color of an object between a
reference source of the same color temperature
(CCT). Lamps that have a high CRI rating provide
better color rendering. |
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| Describes the the apparent color of the
source and the degree of warmth or coolness it
emits. |
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| The expression of effiiency in convering
power (watts) into light (lumens). It is
expressed as lumens per watt. |
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A unit of measure to describe
the color temperature of lamps. Low temperatures
refer to lamps with a large red component which
generally creates a feeling of warmth. High
temperatures refer to lamps will generally
contain more blue and the space will appear
visually cooler. |
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| Refers to the unit of luminous flux. One
lumen is the amount light striking a
one-square-foot area. |
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| The measured luminous output of a brand new
light lamp. |
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The rated life of light sources
is a measurement of the average hours of use for
a lamp. The failure of a lamp occurs when it
will no longer start or keep burning. Over any
specific group of lamps, some will fail sooner
than others, while some may keep burning. The
rated life of lamps is defined in the IESNA
Lighting Handbook, 9th Ed. as "that time when
50% of a large group of lamps are still in
operation." For HID lamps the procedure for
determining rated life uses a "burn cycle" of 11
hours of burning and one hour off. While other
"burn cycles" will produce different results,
this 11on/1off pattern closely resembles the
pattern for outdoor lighting. Typically, outdoor
lighting is switched on at dusk and off at dawn,
so the average burn period is around 12 hours
each day, corresponding to 4,380 hours over each
calendar year (actual hours are slightly less,
around 4,200).
Metal Halide (MH) lamps are
sensitive to position, and the lumen output,
efficacy and rated life are different for
vertical or horizontal lamp positions. A 100W MH
lamps has 15,000 hours life in the vertical
position and 11,250 hours in the horizontal
position. This means the horizontal rated life
is only 75% of the vertical lamp rated life for
these 100W MH lamps.
High Pressure Sodium (HPS)
lamps are not sensitive to burning position.
Tthe rated life is 24,000+ hours, which means
that at 24,000 hours the testing ended with
two-thirds of the lamps still burning.
Using 4,200 hours as a typical
annual burn total, the corresponding maintenance
period for lamps can be estimated. For these
100W MH lamps, the values are 3.6 for vertical
position and 2.7 for horizontal position, and
for HPS 5.7 years. Lamp life for other wattages
of MH sources will be different than for these
100W lamps in this example, with smaller wattage
lamps having equal or shorter life and higher
wattage lamps having longer life, up to 20,000
hrs. HPS lamp life is consistently 24,000+
hours. |
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| Source |
Description |
Rated Life
(hrs) |
Maintenance Period
(4,200
hrs/yr) | |
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| MP |
100W
vertical |
15,000 |
3.6
years |
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100W horizontal |
11,250 |
2.7 years |
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| HPS |
100W (any position) |
24,000 |
5.7 years (or
more) | | |
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The average light output of a
lamp over its rated life. Based on the shape of
its lumen depreciation curve, mean lumens are
measured at 40% of rated lamp life for
fluorescent and metal halide lamps. For mercury,
high-pressure sodium and incandescent lamps,
mean lumen ratings refer to lumens at 50% of
rated lamp life. |
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The amount of light expected
from a particular version of the manufacturer's
lamp under ideal and closely constrained
conditions. |
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| Scotopic/Photopic (S/P)
Ratio | |
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This measurement accounts for
the fact that of the two light sensors in the
retina, rods are more sensitive to blue light
(scotopic vision) and cones to yellow light
(photopic vision). The scotopic/photopic (S/P)
ratio is an attempt to capture the relative
strengths of these two responses. S/P is
calculated as the ratio of scotopic lumens to
photopic lumens for the light source on an ANSI
reference ballast. Cooler sources (higher color
temperatures lamps) tend to have higher values
of the S/P ratio compared to warm sources.
Using 4,200 hours as a typical
annual burn total, the corresponding maintenance
period for lamps can be estimated. For these
100W MH lamps, the values are 3.6 for vertical
position and 2.7 for horizontal position, and
for HPS 5.7 years. Lamp life for other wattages
of MH sources will be different than for these
100W lamps in this example, with smaller wattage
lamps having equal or shorter life and higher
wattage lamps having longer life, up to 20,000
hrs. HPS lamp life is consistently 24,000+
hours.
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