Light Comparison Table - Second Sun

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When reviewing lighting, it is necessary to understand that amount of light (as indicated by a light meter) is far from the only factor to consider. Using a series of different 100 watt fixtures, and assuming an indoor lighting scenario of 30 to 60 foot candles the following can be concluded:

100 Watt Light Source	Photopic Lumens (1)	Correction Factor (2)	Pupil Lumens	Effective Usable Pupil Lumens (3)	Mean Effective Pupil Lumens (20K hours on) (4)
Second Sun LED	14,400	2.00	28,800	28,000	27,936
High-Pressure Sodium (HPS)	10,100	0.57	5,757	4,606	4,145
Metal Halide (MH)	8,500	1.49	12,665	10,132	6,586
4100k T5 Fluorescent (T5 4x4)	9,000	1.62	14,580	10,206	9,185
5000k T8 Fluorescent (T8 6x4)	7,000	1.58	11,060	7,742	6,968

(1) PHOTOPIC LUMENS (What light meters read)

This is what most people considered to be visible light for many years, but that is far from true. The light registered by the cones in the eye (mostly disregarding color) is know as photopic lumens. This is only a true measure of perceived light in the situation where light is very strong (such as sunlight).

SCOTOPIC LUMENS (What was considered irrelevent for years)

In extremely low light levels where the pupil is fully open, the rods of the eye determine visibility. The levels associated with this light are known as scotopic lumens.

(2) CORRECTION FACTOR

In real indoor lighting situations, both rods and cones function to determine visibility. This mix of the two levels is known as mesopic lumens or commonly referred to today as pupil lumens. Many studies have been performed to come up with correction factors that normalize light meter (Photopic Lumen) readings to Pupil Lumens for typical indoor lighting situations.

(3) EFFECTIVE USABLE PUPIL LUMENS

In addition, most light sources are 360 degree output. Lumens are measured on the bulb, not the fixture. Since all light bounced back into the bulb is lost, and any reflected light is somewhat attenuated (reduced), most fixtures do not have the same effective usable lumens as output lumens. At Second Sun, we use the already directional lumen output positioned as needed to produce maximum usable lumens (we do not use reflectors in our manufacturing and warehouse lighting).

(4) MEAN EFFECTIVE PUPIL LUMENS

The last factor to consider is mean lumens. All lights have some light loss over time. Some are extreme. You must consider the mean lumen output and not the initial lumen output as is indicated in all specification sheets.