BUILD A
            F U L L - S P E C T R U M            
LIGHT SOURCE

THE PROBLEM

Energy-efficient lights have poor spectral response

The problem with artificial light sources is that they do not produce a full spectrum of visible light. The sources that produce nearly a full spectrum are being phased out for environmentalist reasons. They are being replaced by new, more energy-efficient light sources. The law now prohibits manufacture of many of the old "inefficient" sources.

A related problem is providing a light source that people with defective color vision can use. This is shown here.

Another related problem is providing a light source that simulates defective color vision. This is shown here.

The new sources that are intended to replace the old sources do not emit light at all visible wavelengths. They have gaps in their spectral responses. Some of the new sources have bright lines at 5 to 9 specific single-line wavelengths, with no output at any other wavelengths. While those wavelengths have been chosen to fool the eye into seeing white, these lamps do not properly render all colors. This causes problems when colors must be identified or matched. In extreme cases, the color of an object can be perceived as a totally different color under a different light.

Unfortunately, the features that make a lamp more efficient also make the light curve choppy or put gaps in the spectrum. Environmentalists don't care that some people need flat-response light sources. They are afraid that our energy use (rather than some natural cause) is warming the planet.

Spectra used to make the approximations shown here were obtained with these methods:
Build a Spectroscope

Simulations of approximate spectra of the various sources are shown here, along with the source name and characteristics:

                                                   

Natural Daylight Full Spectrum (What we want)

                                                   

Incandescent Dim at blue end To be discontinued

                                                   

Halogen Less blue Gets very hot

                                                   

Old Cool White Fluorescent Choppy spectral response To be discontinued

                                                   

Old Warm White Fluorescent Choppy spectral response To be discontinued

                                                   

Daylight CFL Bright line spectrum Compact Fluorescent

                                                   

Soft White CFL Bright line spectrum Compact Fluorescent

                                                   

LED Phosphor Daylight Gap in spectrum  

                                                   

LED Phosphor Soft White Gap in spectrum  

                                                   

LED Tricolor Gaps in spectrum  

                                                   

Blue Hg Phosphor CFL Specialty party bulb Feit, other brands

                                                   

Blue Hg-Ar Phosphor CFL Specialty party bulb TCP, other brands

                                                   

Blue Filtered Daylight CFL Specialty party bulb Cheap brands

                                                   

Teal Incandescent Specialty party bulb Limited availability

                                                   

Blue Feit LED Specialty party bulb Limited availability

                                                   

Cyan CFL Specialty party bulb Limited availability

                                                   

Theoretical Ideal Full Spectrum (What we want)

The problem is finding a light source, or combining available light sources, to produce a reasonably flat response.

WHY DO WE NEED IT?

What looks white is not always white.

Here are some examples of how poor light sources cause troubles:

  1. People assembling electronic components can't read the color codes identifying the various parts and wires under the new lights. They insert the wrong parts or wires, because they can't tell the different color codes apart. Repairmen have the same troubles.
  2. Military uniforms supplied by different suppliers match under some lights, but not under other lights.
  3. Plastic and metal parts of cars (and other products) match under some lights but not under other lights. The cars and other products look cheaply made under the lights where the parts don't match.
  4. Artists paint paintings that unintentionally have colored objects in them that change color when viewed under different lights.
  5. Color photography renders some colors wrong in photos taken under the new light sources. Some light sources produce photos that have no colors except whites, grays, blacks, oranges, browns, and blues. Digital photography is especially affected by the new light sources.
  6. Photographs of colored objects sometimes show the wrong colors when viewed under some of the new light sources.
  7. The page author has a forest green umbrella that looks steel blue under certain white LED lamps.
  8. The page author has conducted The Crayon Trials to show how different lights change the appearance of the colors found in a box of 64 Crayola® crayons. The results are enlightening.
  9. Some objects that look white in sunlight appear colored under some of these new light sources.
  10. Room decor looks very different than intended when the old incandescent lamps are replaced with new energy-saving bulbs. Colors are changed, and colors that formerly looked good together now clash with the new lamps.
  11. The gaps in the spectrum cause eyestrain in people with presbyopia (lack of lens accommodation).
  12. Some scientific tests of materials or pigments need spectrally-flat light sources.
  13. Colorimetry requires a spectrally-flat light source.
  14. Even if a reflection or absorption spectrometer can compensate for variations in the intensity that occur at different wavelengths of the light source measured, it can't compensate for gaps in the spectrum where there are no emissions at all.

HOW TO MAKE A FLAT-SPECTRUM SOURCE

Fortunately, the needed lamps are available

The following light sources can be combined to remove the spectral gaps:

                                                   

LED Phosphor Daylight    

                                                   

LED Phosphor Soft White    

                                                   

Blue Hg Phosphor CFL Specialty party bulb Feit, other brands

                                                   

Blue Hg-Ar Phosphor CFL Specialty party bulb TCP, other brands

                                                   

Cyan CFL Specialty party bulb Limited availability

                                                   

Blue Feit LED Specialty party bulb Limited availability

Check the spectra of the LED and CFL colored lamps that you use. Different brands, and different products by the same brand, can have totally different spectra.

The following combinations produce light at most visible locations:

                                                   

LED Phosphor Daylight - combined with - Blue Hg Phosphor CFL

                                                   

LED Phosphor Soft White - combined with - Blue Hg Phosphor CFL

                                                   

All three: LED Phosphor Daylight, LED Phosphor Soft White, and Blue Hg Phosphor CFL

                                                   

All three: LED Phosphor Daylight, LED Phosphor Soft White, and Cyan Hg Phosphor CFL

                                                   

All three: LED Phosphor Daylight, LED Phosphor Soft White, and Blue LED

                                                   

Theoretical Ideal Full Spectrum (What we want)

The teal incandescent lamp could be used here, but there are two limitations on its use:

HOW TO MAKE AN EXTENDED FULL-SPECTRUM SOURCE

Fortunately, the needed lamps are available for this too

The following light sources can be added to fill in the missing ends of the spectrum:

                                                   

All three above: LED Phosphor Daylight, LED Phosphor Soft White, and Blue LED

                                                   

TCP Blue Hg-Ar Phosphor CFL

                                                   

Feit Red CFL

                                                   

All five: LED Phos. Daylight, LED Phos. Soft White, Blue LED, Blue CFL, and Red CFL

                                                   

Theoretical Ideal Full Spectrum (What we want)

If this setup has a problem, it is that the overall color balance is slightly purple. The red and blue lamps slightly overpower the greens in the white lamps. Adjust it by changing the lumen output of the white LEDs selected or covering parts of lamps.

BUILDING A LAMP ARRAY

Selecting the color circuits needed

The complexity of the system you make depends on your needs. For identifying colors only one combination of lighted lamps may be needed. For color matching or the creation of art, many different circuits may be used. Here are some suggestions of what to use:

Designing a fixture

Any of the following can be used to provide a fixture to hold the lamps:

Wiring the circuits for the lamps

lamp circuits The following lamp fixture wiring methods can be used:

lamp switches The following lamp fixture wiring methods can be used:

The Author's Setup

Here is the page author's flat-spectrum setup.
Below it is the modification for full-spectrum use.

Switches off Switches off

The page author used an old store display fixture he got at a store-closing sale for a dollar. It is hung on the front of what used to be a cove lighting system. The cove lighting is no longer used because the Obama administration banned the lamps that fit it.

lamp switches The switchbox is designed to switch four kinds of lamps. The author later changed the function of one of the switches to gain full-spectrum operation:

FLAT SPECTRUM FULL-SPECTRUM FLATTENED-SPECTRUM POSITIONS SWITCHES
Daylight CFL Red CFL & Blue CFL LED "Full Spectrum" 1 & 8 CFL
LED Soft White LED Soft White LED Soft White 3 & 5 WARM
LED Daylight LED Daylight LED Daylight 4 & 6 COOL
Blue LED Blue LED Blue LED 2 & 7 BLUE
none none Red CFL & Blue CFL External EXT

Photos of what the lamps look like when on, with approximate spectral distribution:

FLAT-SPECTRUM
DISPLAYPHOTOSPECTRUM  CFL WARM COOLBLUE 
All lights off Switches off

                                                   

OFFOFF OFFOFF 
Blue on Blue on

                                                   

OFFOFF OFFON 
Flat-spectrum
(All but CFL)
Flat-spectrum

                                                   

OFFON ONON 
CFL on CFL on

                                                   

ONOFF OFFOFF 
All lights on All lamps on

                                                   

ONON ONON 
 
FULL-SPECTRUM
DISPLAYPHOTOSPECTRUM  CFL WARM COOLBLUE 
All lights off Switches off

                                                   

OFFOFF OFFOFF 
Flat-spectrum
(All but CFL)
Flat-spectrum

                                                   

OFFON ONON 
Full-spectrum
(All lights on)
Full-spectrum

                                                   

ONON ONON 
 
FLATTENED FULL-SPECTRUM
DISPLAYPHOTOSPECTRUM  CFL WARM COOLBLUE EXT 
Flat-spectrum
(All bar on)
Full-spectrum

                                                   

ONON ONONOFF
Full-spectrum
(All lights on)
Full-spectrum

                                                   

ONON ONONON


Epilogue

The following are minor problems that occurred with this project:

  1. Subsequent tests with the spectroscope show that the blue lamps do not fully fill in the gap in the spectrum. Cyan CFL lamps were substituted. They filled the gap a little better, but it is still there.
  2. Research shows that the eye also has a dip in its response in the same place. This might account for the anomaly.
  3. About 2.5 months after the light was placed in operation, one of the Daylight LED bulbs failed. It started blinking on and off, with the on and off periods being about 5 minutes each.
  4. The returns clerk at the store I bought the bulb at said someone else returned a bulb with the same defect earlier that day.
  5. The replacement bulb, although having a different trademark on it, is identical to the failed bulb. No more bulbs have failed.
  6. About 5 months after the light was placed in operation, Feit Electric started making a blue LED that also produces cyan light at a brightness close to that of the cyan CFLs. These were installed in place of the cyan CFLs. They fill in the gap much better, with very little duplication of wavelengths, and do not give off the spectral green spike of mercury vapor the cyan CFLs gave off.
  7. About 8 months after the light was placed in operation, the page author discovered red CFLs made by Feit Electric and blue CFLs made by TCP that can extend the ends of the spectrum, so the lamp can give off all visible wavelengths. They give off only tiny amounts of the green spike of the mercury line. He replaced the Daylight CFLs with these lamps.
  8. About a year after the lights were put into operation, the Feit red CFLs and TCP blue CFLs, along with an extra Feit Blue LED were put into an auxillary three-lamp fixture on a separate switch. Sylvania "Ultra full spectrum" daylight LEDs were put in the sockets originally containing the daylight CFLs. For normal use, all of the lights on the light bar are used. The extra fixture is used with the entire bar for a fully flat spectrum. This is called Flattened Full Spectrum in the tables above.
  9. With the frequency of companies introducing and discontinuing products in this kind of product line, the question of being able to replace these lamps when they fail has risen. It might be a good idea to stock up on replacements. The two Feit LEDs and the Sylvania full-spectrum LED used have already disappeared from the market. New versions of the Feit lamps have appeared, but Sylvania stopped making the full-spectrum series.
  10. Other colored LED lamps have appeared on the market. The ones made by Polaroid and illumin8 do not give off the cyan light needed to fill the gap. They are not substitutes for the Feit blue LED.




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