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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. These were available in April 2013 when I started these experiments:
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Natural Daylight |
Full Spectrum |
(What we want) |
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Incandescent |
Dim at blue end |
To be discontinued |
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Halogen |
Less blue |
Gets very hot |
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Old Cool White Fluorescent |
Choppy spectral response |
To be discontinued |
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Old Warm White Fluorescent |
Choppy spectral response |
To be discontinued |
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Daylight CFL |
Bright line spectrum |
Compact Fluorescent |
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Soft White CFL |
Bright line spectrum |
Compact Fluorescent |
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LED Phosphor Daylight |
Gap in spectrum |
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LED Phosphor Soft White |
Gap in spectrum |
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LED Tricolor |
Gaps in spectrum |
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Blue Hg Phosphor CFL |
Specialty party bulb |
Feit, other brands |
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Blue Hg-Ar Phosphor CFL |
Specialty party bulb |
TCP, other brands |
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Blue Filtered Daylight CFL |
Specialty party bulb |
Cheap brands |
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Teal Incandescent |
Specialty party bulb |
Limited availability |
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Blue Feit LED |
Specialty party bulb |
Limited availability |
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Cyan CFL |
Specialty party bulb |
Limited availability |
|
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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:
- 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.
- Military uniforms supplied by different suppliers match under some lights, but not under other
lights.
- 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.
- Artists paint paintings that unintentionally have colored objects in them that change color
when viewed under different lights.
- 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.
- Photographs of colored objects sometimes show the wrong colors when viewed under some of the
new light sources.
- The page author has a forest green umbrella that looks steel blue under certain white LED
lamps.
- 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.
- Some objects that look white in sunlight appear colored under some of these new light
sources.
- 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 under the new lamps.
- The gaps in the spectrum cause eyestrain in people with presbyopia (lack of lens
accommodation).
- Some scientific tests of materials or pigments need spectrally-flat light sources.
- Colorimetry requires a spectrally-flat light source.
- 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:
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LED Phosphor Daylight |
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LED Phosphor Soft White |
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Blue Hg Phosphor CFL |
Specialty party bulb |
Feit, other brands |
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Blue Hg-Ar Phosphor CFL |
Specialty party bulb |
TCP, other brands |
|
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Cyan CFL |
Specialty party bulb |
Limited availability |
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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:
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LED Phosphor Daylight - combined with - Blue Hg Phosphor CFL |
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LED Phosphor Soft White - combined with - Blue Hg Phosphor CFL |
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All three: LED Phosphor Daylight, LED Phosphor Soft White, and Blue Hg Phosphor
CFL |
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All three: LED Phosphor Daylight, LED Phosphor Soft White, and Cyan Hg Phosphor
CFL |
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All three: LED Phosphor Daylight, LED Phosphor Soft White, and Blue LED |
|
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Theoretical Ideal Full Spectrum (What we want) |
The teal incandescent lamp could be used here, but there are two limitations on its use:
- It might not be easily available.
- It will require more frequent replacement than the other sources. If the sources are mounted
in a high location, this might be an inconvenience.
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:
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All three above: LED Phosphor Daylight, LED Phosphor Soft White, and Blue LED |
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TCP Blue Hg-Ar Phosphor CFL |
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Feit Red CFL |
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All five: LED Phos. Daylight, LED Phos. Soft White, Blue LED, Blue CFL, and Red CFL |
|
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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:
- For color identification, use one or more of these combinations (found in the table above):
- LED Phosphor Daylight combined with Blue LED
- LED Phosphor Soft White combined with Blue LED
- LED Phosphor Daylight, LED Phosphor Soft White, and Blue LED
- LED Phosphor Daylight, LED Phosphor Soft White, and Blue LED, Blue CFL, and Red CFL
If more than one combination is needed, use switches to select the combination to use.
- For color matching or creating art, you might want the capability to use many of the following
light sources, with the ability to switch them in and out.
- LED Phosphor Daylight combined with Blue LED
- LED Phosphor Soft White combined with Blue LED
- LED Phosphor Daylight, LED Phosphor Soft White, and Blue LED
- LED Phosphor Daylight, LED Phosphor Soft White, and Blue LED, Blue CFL, and Red CFL
- Halogen
- Daylight CFL
- Soft White CFL
- LED Phosphor Daylight
- LED Phosphor Soft White
- Blacklight CFL (to test for fluorescent effects)
- Outdoor daylight (take the samples outside or open a north-facing skylight)
- Sunlight (take the samples outside or open a south-facing skylight)
- Cool White Old-Style Fluorescent
- Warm White Old-Style Fluorescent
- Mercury Vapor
- High Pressure Sodium Vapor
- HID (High Intensity Discharge)
- LED Tricolor
- Incandescent
- Low Pressure Sodium Vapor
- Induction Plasma
The ones usually needed the most are at the top of the list.
Designing a fixture
Any of the following can be used to provide a fixture to hold the lamps:
- A wall-mount fixture with many sockets, rewired for multiple circuits
- A chandelier or two, with many sockets, multiple circuits, used with a white ceiling
- Track lights with multiple circuits
- Multiple-bulb floor lamps rewired for multiple circuits
- Theatrical vanity mirror light strips with multiple circuits
- Multiple gooseneck desk lamps
- Individual rosette lamp sockets with individual switched circuits
- Anything else you might already have handy
Wiring the circuits for the lamps
The following lamp fixture wiring methods can be used:
- A portable fixture can be built with multiple lamp sockets and a pendant control box for
switching the various kinds of lamps (top diagram).
- Permanent wiring can be used with gang boxes for multiple toggle switches and multiple
porcelain rosette sockets on round boxes for the individual lamps (bottom diagram). Note that
the safety ground wiring (required) is not shown.
- Permanent wiring can also be used with gang boxes for multiple toggle switches and multiple
track lighting sets for the individual lamp circuits (bottom diagram). Again, the safety ground
wiring is not shown.
- Translucent diffusers can be used to blend the light from the bulbs. But diffusers must be
checked, to be sure they do not block or darken some colors. Also check what happens to the
diffuser when exposed to ultraviolet light. Some plastics become brittle or turn yellow.
- Cove lighting with a known true white ceiling can diffuse the light.
The following lamp fixture wiring methods can be used:
- A portable fixture can use a pendant control box for switching the various kinds of lamps
(top diagram above, and at right).
- A portable fixture can be built with individual pull-chain switches to turn on and off
the various kinds of lamps (top diagram above, without the cable).
- A portable fixture can be built with a rotary switch to select the various kinds of lamps.
Separate switches are needed for the blue CFL, the Soft White LED, and the blacklight CFL, so
they can be combined with other sources.
- Permanent wiring can be used with gang boxes for multiple toggle switches.
- The page author's switch box is shown at right.
The Author's Setup
Here is the page author's flat-spectrum setup.
Below it is the modification for full-spectrum use.
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.
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 |
| DISPLAY | PHOTO | SPECTRUM |
CFL | WARM |
COOL | BLUE | |
| All lights off |
 |
|
OFF | OFF |
OFF | OFF | |
| Blue on |
 |
|
OFF | OFF |
OFF | ON | |
Flat-spectrum
(All but CFL) |
 |
|
OFF | ON |
ON | ON | |
| CFL on |
 |
|
ON | OFF |
OFF | OFF | |
| All lights on |
 |
|
ON | ON |
ON | ON | |
| |
| FULL-SPECTRUM |
| DISPLAY | PHOTO | SPECTRUM |
CFL | WARM |
COOL | BLUE | |
| All lights off |
 |
|
OFF | OFF |
OFF | OFF | |
Flat-spectrum
(All but CFL) |
 |
|
OFF | ON |
ON | ON | |
Full-spectrum
(All lights on) |
 |
|
ON | ON |
ON | ON | |
| |
| FLATTENED FULL-SPECTRUM |
| DISPLAY | PHOTO | SPECTRUM |
CFL | WARM |
COOL | BLUE | EXT |
Flat-spectrum
(All bar on) |
 |
|
ON | ON |
ON | ON | OFF |
Full-spectrum
(All lights on) |
 |
|
ON | ON |
ON | ON | ON |
Epilogue
The following are minor problems that occurred with this project:
- 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.
- Research shows that the eye also has a dip in its response in the same place. This
might account for the anomaly.
- 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.
- The returns clerk at the store I bought the bulb at said someone else returned a
bulb with the same defect earlier that day.
- The replacement bulb, although having a different trademark on it, is identical to
the failed bulb. No more bulbs have failed.
- 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.
- 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.
- 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.
- 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 Feit Soft White and Daylight 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.
- 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.
- By September 2017, all of the products used in these lights were discontinued or no longer
carried by stores in my area. New versions of the white LEDs can be found, but none of the
colored ones are still on the market. This is what I hate about mass marketing. We never had
products disappear with incandescent bulbs.
LINKS
