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The spectra of fluorescent lamps
 

Cool white deluxe spectrum graph


The graph of the spectrum from a typical "Cool-white Deluxe" fluorescent lamp shows the wavelengths in nanometers along the horizontal axis and the energy emission in Watts per ten nanometer-band as the vertical axis. The example shown is from Sylvania, but the spectra of the same lamp type from its other manufacturers are virtually identical.

 

The five rectangular bars that stick out above the smooth curve of the broadband spectrum average the mercury emission lines as columns ten nanometers wide because the graph would otherwise become to tall.  They are really very narrow spikes, a great many times taller and thinner than on this graph, and they are virtually the same for most types of fluorescent tubes, such as "Daylight" or "Cool White Deluxe", etc..  The major difference between those types is in the shape of the broadband curve which can be shifted somewhat by using different phosphor mixtures to obtain different color temperatures, but the main emission lines are not much affected by these manipulations.

 

Compact fluorescent lamps (CFLs) exhibit greater variations in the relative proportions of these spikes than the fluorescent tubes, but most of the spectra I saw include the strong spike at 435.8 nanometer.  You can find a collection of spectra from some of  the different CFL models at http://ledmuseum.candlepower.us/led/ledleft.htm  (Scroll down to the sub-heading “MISCELLANEOUS LIGHT AND NON-LIGHT-EMITTERS”, slightly more than ¾ down in the navigation panel at left; click there on the link to “Spectra of fluorescent lite bulbs”; for comparison, the spectra of sunlight and of some incandescent bulbs are shown at the link to “Spectra of other light sources” under the same sub-heading.  These spectra have been measured from individual samples submitted by readers of that site and are not necessarily representative of that model’s entire production or of the manufacturer’s specifications intended for it.  They are also not necessarily representative of the full variety available in CFLs.) (accessed Jan. 01, 2010))

The spectra shown there range from having the tallest mercury emission line at 435.8 nanometers, as tall or even taller than in the fluorescent tube spectra, in models such as “Dollar Store” Sunbrite “warm white” 3000oK 18W and Trisonic “soft white” 6500oK 30W, to third tallest in such CFL models as Osram 2700oK 9W, TCP 2700oK 23W, Philips 4100oK  and 5000oK 13W, Commercial Electric 14W, and N:Vision “Daylight” 5500oK 9W.  However, the presence of even taller spikes in longer wavelengths does not render the emission lines at 435.8 nm harmless since any excess exposure to this wavelength has been shown again and again to cause significantly more retinal damage to normal adult eyes than similar exposures to any other part of the visible spectrum.  (See the list of damage-weighted "blue-light-hazard" values in Table 1 below.)

 

Children's eyes are still more transparent to all blue and shorter wavelengths, including even some of the even more energetic near-ultraviolet light which adults cannot see, by definition.  In their case, the retinal damage potential is shown in the "Aphakic eye" columns in the above-linked Table of damage-weighted retinal irradiances.

Many fluorescent tubes emit only small amounts of energy in the ultraviolet range below 400 nanometer, as in the above graph and the Table below, but others have stronger emissions in that region that are not fully filtered by their glass wall or their plastic diffuser.

 

 


Table 1.: Damage weighted irradiance from the "Deluxe Cool White" fluorescent lamp
which the American Academy of Pediatrics specifies for intensive care nurseries.

Wave-length in nano-meters Irradiance in Watts per 10 nm, scaled from graph Blue-light hazard function for normal eye Blue-light damage-weighted irradiance Aphakic eye photic hazard function Aphakic eye damage- weighted irradiance

 

 

 

 

 

 

315

0.122

--

--

6.00

0.7320

355

0.122

--

--

5.22

0.6368

365

0.955

--

--

4.29

4.0970

375

0.321

--

--

3.56

1.1428

385

0.416

--

--

2.31

0.9610

395

0.581

invisible ultraviolet 

1.58

0.9180

400

--

0.10

--

1.43

 

405

2.432

0.20

0.4864

1.30

3.1616

410

--

0.40

--

1.25

 

415

0.959

0.80

0.7672

1.20

1.1508

420

--

0.90

--

1.15

 

425

1.137

0.95

1.0802

1.11

1.2621

430

--

0.98

--

1.07

 

435

6.120

1.00

6.1200

1.03

6.3036

440

--

1.00

--

1.00

 

445

1.338

0.97

1.2979

0.97

1.2979

450

--

0.94

--

0.94

 

455

1.440

0.90

1.2960

0.90

1.2960

460

--

0.80

--

0.80

 

465

1.527

0.70

1.0689

0.70

1.0689

470

--

0.62

--

0.62

 

475

1.650

0.55

0.9075

0.55

0.9075

480

--

0.45

--

0.45

 

485

1.727

0.40

0.6908

0.40

0.6908

490

--

0.22

--

0.22

 

495

1.839

0.16

0.2942

0.16

0.2942

500

--

0.10

--

0.10

 

505

1.935

--

0.2419

 

0.2419

515

1.990

--

0.0995

 

0.0995

525

2.118

--

0.0678

 

0.0678

535

2.233

--

0.0447

 

0.0447

545

4.307

--

0.0560

 

0.0560

555

2.476

--

0.0198

 

0.0198

565

2.598

--

0.0130

 

0.0130

575

3.179

--

0.0095

 

0.0095

585

2.905

--

0.0058

 

0.0058

595

2.991

--

0.0030

 

0.0030

600

--

0.01

--

0.01

 

605

3.073

--

0.0031

 

0.0031

615

3.029

--

0.0030

 

0.0030

625

2.952

--

0.0030

 

0.0030

635

2.808

--

0.0028

 

0.0028

645

2.664

--

0.0027

 

0.0027

655

2.355

--

0.0024

 

0.0024

665

2.074

--

0.0021

 

0.0021

675

1.548

--

0.0015

 

0.0015

685

1.021

--

0.0010

 

0.0010

695

0.188

--

0.0002

 

0.0002

700

--

0.001

--

0.001

 

 

 

 

 

 

 

Total

71.130 Watt

 

14.6 Watt

 

26.5 Watt

% of output

100%

 

20.51%

 

37.26%

 

 

 

 

 

 

 

Column 1 in this Table lists the wavelengths in nanometers (nm) in which the “Cool White Deluxe” lamp emits its radiation.

Column 2 shows the energy of that emission in Watts for each wavelength interval of ten nm. Please note the emission spike at 435 nm.

The third column gives the U.S. Occupational Safety Guidelines' action spectrum for the "blue-light hazard function" which the National Institute for Occupational Safety and Health (NIOSH) first published in 1980. It shows the maximum vulnerability range from 435 to 440 nm where the emission from the lamp is strongest [SLINEY DH, WOLBORSHT ML. Safety standards and measurement techniques for high intensity light sources. Vision Res 1980: 20: 1133-41 (see page 1137)] .

The fourth column multiplies the irradiance from the lamp in column 2 with the value of that “blue-light hazard function” in column 3 to obtain the "damage-weighted irradiance" from that wavelength band that reaches the retina in a normal adult eye. The lens of that eye is usually yellowed and so filters out much of the most damaging blue and violet radiation.

Column 5 lists the corresponding photic hazard function for aphakic eyes, that is, eyes like those of children whose lens is not yet yellowed and therefore lets through the even more damaging radiation at shorter and therefore more energetic wavelengths.

The last column lists the damage-weighted irradiance from those fluorescent nursery lamps on the retinae of unprotected eyes like those of children.

Continue to a discussion of damage-weighted irradiance and its effects on the retinae of premature babies when their still developing eyes are at their most vulnerable stage.