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Westinghouse Caution Yellow mercury lamp in operation (view 1) Caution Yellow mercury lamps were a thing before the advent and widespread use of high-pressure sodium lamps. Those lamps were made with a color filter (an external lacquer in the case of the present Westinghouse H33-1-GL/Y, shown [url=https://trad-lighting.net/gallery/displayimage.php?pid=1120]here[/url] on display) so as to produce a saturated yellow light color that was used for the illumination of dangerous road sections. The picture above shows the lamp in operation (see top view [url=https://trad-lighting.net/gallery/displayimage.php?pid=1165]there[/url]), its light color is produced by a combination of mercury's green (546 nm) and yellow (577 & 579 nm) lines and the red fluorescence of the magnesium fluorogermanate phosphor peaking around 655 nm. Such light was well suited for traffic lighting back in the 1960s as its yellow color contrasts very strongly with that of other mercury lamps (especially clear ones), which helped raise drivers' awareness, and its red content enabled a good identification of emergency vehicles. Keywords: Lamps

Westinghouse Caution Yellow mercury lamp in operation (view 1)


Caution Yellow mercury lamps were a thing before the advent and widespread use of high-pressure sodium lamps. Those lamps were made with a color filter (an external lacquer in the case of the present Westinghouse H33-1-GL/Y, shown here on display) so as to produce a saturated yellow light color that was used for the illumination of dangerous road sections. The picture above shows the lamp in operation (see top view there), its light color is produced by a combination of mercury's green (546 nm) and yellow (577 & 579 nm) lines and the red fluorescence of the magnesium fluorogermanate phosphor peaking around 655 nm. Such light was well suited for traffic lighting back in the 1960s as its yellow color contrasts very strongly with that of other mercury lamps (especially clear ones), which helped raise drivers' awareness, and its red content enabled a good identification of emergency vehicles.
DSCF0281m.jpg DSCF0289m.jpg Westinghouse_H33-1-GL21Y_1m.jpg Westinghouse_H33-1-GL21Y_2m.jpg DSCF0262m.jpg
Lamp/Fixture Information
Manufacturer:Westinghouse
Model Reference:H33-1-GL/Y
Lamp
Lamp Type:Mercury high pressure fluorescent (caution yellow)
Filament/Radiator Type:Thermal discharge in argon and mercury vapor, and fluorescence
Base:E39
Shape/Finish:Bulged tubular fluorescent, color coated
Service Life:24 kh
Burning Position:Universal
Electrical
Wattage:400 W
Voltage:140 V
Current:3.2 A
Optical
Lumen Output:11,000 lm (initial)
Lumen Efficacy:27.5 lm/W (initial)
Colour Temperature:3260 K (yellow)
Colour Rendering Index:41 Ra8
Physical/Production
Factory Location:Bath, NH, USA
Fabrication Date:June 1969
Application/Use:Street lighting (illumination of dangerous sections)
File information
Filename:Westinghouse_H33-1-GL21Y_1m.jpg
Album name:Max / Misc lamps and lighting
Keywords:Lamps
Filesize:914 KiB
Date added:30 Mar 2026
Dimensions:1014 x 1500 pixels
Displayed:52 times
Software:Adobe Photoshop 25.7 (Windows)
URL:https://trad-lighting.net/gallery/displayimage.php?pid=1166
Favourites:Add to Favourites

Comment 1 to 9 of 9
Page: 1

Ria   [Mon 30 Mar 2026 at 12:18]
Fascinating history as always Max, I don't think we ever had anything like this over here.
Eric   [Mon 30 Mar 2026 at 14:11]
Great to see a lit photo of this lamp! Mercury Vapour Lamp
Tuopeek   [Mon 30 Mar 2026 at 16:13]
Mercury discharge lamps don't suggest yellow to me Very Happy but I guess it works. I have wondered if the fluorescent coating was selected to enhance yellow but I think you are inferring it's just the usual red mercury fluorescent underneath .
Max   [Mon 30 Mar 2026 at 17:42]
That really depends on the lamp and the manufacturer. In the present case the phosphor is indeed the regular red-emitting magnesium fluorogermanate that was also used in standard color-corrected mercury lamps (\C type in the North America). Some yellow mercury lamps were briefly sold without phosphor coating, but those were more greenish, thus less suitable for streetlighting since emergency vehicles appeared brownish under their red-deficient light. Some manufacturers employed an orange-emitting fluorescent material (e.g. calcium strontium magnesium orthophosphate for Tesla in Czechoslovakia), which caused the same issue as for the clear yellow lamps. As a result, those were used primarily in industrial settings to improve visual acuity under dusty conditions, especially where low-pressure sodium lamps where uncommon (North America, Eastern Bloc, Soviet Union, etc).

Eric - That's not a recent shot... this picture is nearly two decades old!

Ria - Those lamps where certainly not used in Western Europe as low-pressure sodium lamps where much more effective and economical (an SO-I 140W produces more light than the present 400 W H33-1-GL/Y!).
Eric   [Mon 30 Mar 2026 at 19:30]
@Max - Your pic is way better than my pic of said lamp... Laughing
Max   [Wed 01 Apr 2026 at 06:22]
That's not wrong lol.
AgentHalogen_87   [Wed 01 Apr 2026 at 17:10]
That's a very cool lamp! It makes perfect sense, but seems backwards to me, as I grew up with everywhere being lit by sodium, and high important areas like pedestrian crossings were highlighted by white light
wide-lite 1000   [Thu 02 Apr 2026 at 02:48]
WOW ! I've never seen one of these lit ! Mind Blown
Max   [Sat 04 Apr 2026 at 08:28]
Very few have Cool

Comment 1 to 9 of 9
Page: 1