Alliance for Lighting Information

Rayleigh Scatter Index (RSI) Data for Sources

by David M. Keith

Rayleigh Scatter Index (RSI) is a metric for comparing the probability of atmospheric scatter of radiation under clear sky conditions.

The RSI evaluation at each wavelength can be summed over the entire spectrum or used as SPDs of the radiation "reflected" by the sky. In all cases the resulting values are only suitable for comparisons and the absolute values should not be considered as having merit in themselves, because the constant used in these RSI calculations is chosen strictly for convenience and has no other numerical basis. However, using the analysis basis of "all other things being equal", by starting with "equal amounts" and treating them all the same, the values do have merit for comparisons.

The following tables shows the evaluations for different sources' SPDs - all scaled to the same 100 photopic lumens - as photopic lumens (Pho), as scotopic lumens (Sco) and as meltopic units (Mel) and then the RSI summation overall (RSIrad), followed by the results of the "reflected SPDs" evaluated again with photopic (RSIpho) or scotopic (RSIsco) or meltopic (RSImel) sensitivity functions. The sources are also described in colormetric terms by CCT, and more details are available here.

Name			CCT	Watts	Pho	Sco	Mel	RSIrad	RSIpho	RSIsco	RSImel

Skylight			11385	0.55	100	297	0.18	5.5	5.7	26	1.9
Daylight (D65)		6502	0.49	100	246	0.14	3.8	5.5	21	1.4
LED cool white		6273	0.31	100	209	0.12	2.1	5.4	17	1.2
Fluorescent 6500K		6088	0.32	100	218	0.12	2.5	5.4	18	1.2
LED			5899	0.30	100	191	0.11	2.1	5.3	16	1.2
Sunlight			5517	0.49	100	228	0.12	3.4	5.4	19	1.2
Fluorescent		5193	0.30	100	184	0.10	2.2	5.3	15	1.0
Metal halide		4917	0.35	100	181	0.09	3.1	5.2	14	1.0
LED			4863	0.29	100	173	0.09	1.8	5.2	14	0.9
LED neutral		4466	0.32	100	173	0.09	1.9	5.2	14	0.9
Fluorescent		4452	0.29	100	178	0.08	2.0	5.3	14	0.8
Fluorescent		4415	0.25	100	134	0.07	1.8	5.0	11	0.7
Metal halide		4319	0.32	100	177	0.09	2.5	5.2	14	0.8
Fluorescent		4279	0.36	100	164	0.07	2.3	5.2	12	0.7
Metal halide		4181	0.39	100	184	0.09	2.8	5.2	15	1.0
Metal halide		4160	0.32	100	160	0.08	2.7	5.1	12	0.7
Metal halide		4086	0.39	100	181	0.09	2.6	5.2	14	0.9
Metal halide		4061	0.30	100	150	0.07	2.4	5.1	12	0.7
Fluorescent		4009	0.29	100	159	0.08	1.9	5.1	12	0.8
Metal halide		4002	0.31	100	163	0.08	2.3	5.1	13	0.7
Fluorescent 4100K		3813	0.30	100	162	0.08	2.0	5.1	13	0.8
Metal halide		3776	0.30	100	148	0.07	2.3	5.0	11	0.7
Mercury Vapor coated	3758	0.50	100	118	0.05	3.3	5.0	9	0.6
Ceramic Metal Halide	3618	0.36	100	147	0.07	2.6	5.0	11	0.7
Ceramic Metal Halide	3610	0.36	100	147	0.07	2.7	5.0	11	0.7
Fluorescent		3560	0.28	100	137	0.06	1.9	5.0	10	0.6
Fluorescent 3500K		3326	0.29	100	145	0.07	1.8	5.0	11	0.6
Metal Halide		3068	0.34	100	138	0.06	2.0	4.9	10	0.6
Fluorescent		3056	0.29	100	126	0.05	1.8	4.9	9	0.5
Ceramic Metal Halide	3049	0.33	100	130	0.06	2.0	4.9	9	0.5
Ceramic Metal Halide	3031	0.32	100	130	0.05	2.0	4.9	9	0.5
Fluorescent 3000K		2919	0.28	100	126	0.05	1.7	4.9	9	0.5
Compact Fluor.		2886	0.28	100	114	0.04	1.7	4.9	8	0.4
Ceramic Metal Halide	2874	0.29	100	122	0.05	1.8	4.9	9	0.5
Incandescent CIE_A	2856	0.61	100	141	0.06	2.3	4.9	10	0.5
Incan. Tung. Halogen	2830	0.59	100	138	0.06	2.2	4.9	10	0.5
Incan. Tung. Halogen	2788	0.62	100	138	0.06	2.3	4.9	10	0.5
Incan. Tung. Halogen	2775	0.62	100	137	0.06	2.3	4.9	10	0.5
Incandescent		2709	0.63	100	133	0.05	2.3	4.9	10	0.5
Incan. Neodymium		2604	0.73	100	146	0.06	2.6	4.9	11	0.6
High Pressure Sodium	2174	0.25	100	68	0.03	1.2	4.5	5	0.2
High Pressure Sodium	2116	0.25	100	67	0.03	1.2	4.4	5	0.2
High Pressure Sodium	2108	0.28	100	69	0.03	1.2	4.5	5	0.2
High Pressure Sodium	2061	0.26	100	64	0.03	1.2	4.4	4	0.2
High Pressure Sodium	2060	0.25	100	63	0.03	1.2	4.4	4	0.2
High Pressure Sodium	2056	0.26	100	63	0.03	1.2	4.4	4	0.2
High Pressure Sodium	2005	0.25	100	55	0.02	1.1	4.4	4	0.2
High Pressure Sodium	2001	0.26	100	64	0.03	1.2	4.4	4	0.2
High Pressure Sodium	1998	0.25	100	55	0.02	1.1	4.4	4	0.2
Low Pressure Sodium	1832	0.19	100	25	0.01	0.8	4.2	1	0.0
Low Pressure Sodium	1807	0.19	100	24	0.01	0.8	4.2	1	0.0

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