Why don't arc lamps use phospors to convert the unwanted wavelengths into light - Page 1
Forum section: electronics / beginners

author: Deactivated-1
author_rank: Frequent Contributor
timestamp: May 31, 2023, 11:03:02 pm
content: Wouldn't adding a phosphor coating inside the outer envelope increase the luminous efficiency of the bulb? for example a metal halide or a mercury vapor bulb?

author: TimFox
author_rank: Super Contributor
timestamp: May 31, 2023, 11:25:45 pm
content: The light hitting the phosphor must be at a shorter wavelength than that emitted by the phosphor.Fluorescent lights excite the phosphor with UV, but LEDs use blue.

author: Manul
author_rank: Super Contributor
timestamp: May 31, 2023, 11:32:22 pm
content: I suppose phosphor coating would convert some unwanted UV into visible light, but it would also absorb some of the visible light produced by the lamp. So in the end efficiency would probably be worse. Just my 2 cents.

author: Buriedcode
author_rank: Super Contributor
timestamp: June 01, 2023, 03:10:35 am
content: Quote from: ELS122 on May 31, 2023, 11:42:45 pmIt's already done. Plenty of single colour LEDs are in-fact phosphor coated blue these days. I recently bought a cheapo character LCD and the backlight is a single LED that is extremely bright even at 4mA. Turns out its a lime-green phosphor coating because its spectrum has several wide peaks.

author: coppercone2
author_rank: Super Contributor
timestamp: June 01, 2023, 03:47:11 am
content: you can split it in a expensive prism coupled by a parabolic reflector thing and then seperate out the UV light and phosphor it maybe

author: tooki
author_rank: Super Contributor
timestamp: June 01, 2023, 08:58:48 am
content: Quote from: ELS122 on June 01, 2023, 03:34:08 amAll else held equal, a blue LED is more efficient. That’s why warm white LEDs are less efficient than cool white ones: the warm ones convert a greater share of the blue light to longer wavelengths.But ultimately, it depends on the LED itself. I would assume that the ones intended for lighting and backlights are optimized for efficiency. Those can be phosphor converted to white, or they can be blue, intended for use with a separate phosphor converter. (Look up “remote phosphor” LED lighting.)A small indicator LED might not be as optimized.

author: tszaboo
author_rank: Super Contributor
timestamp: June 01, 2023, 09:25:47 am
content: Probably because the last time arc lamp technology was updated predates the widespread usage of phosphor.You also don't see too many updates to kerosene lamp or pigeon mail.

author: Jwillis
author_rank: Super Contributor
timestamp: June 01, 2023, 12:44:42 pm
content: Quote from: tszaboo on June 01, 2023, 09:25:47 amPhosphor coating has been around since the 30's . And phosphor coated mercury vapour lamps have been around since the 60's at least.Biggest issue with phosphor coating on high temp lamp is the phosphorous losses efficiency at high temperatures.Kind of moot now since mercury lamps are being or have been phased out because of the mercury content.

author: Siwastaja
author_rank: Super Contributor
timestamp: June 01, 2023, 01:03:51 pm
content: Quote from: ELS122 on May 31, 2023, 11:42:45 pmNo, becauseluminous efficiency, by definition, applies a weighing curve which matches human vision. Deep blue as used in white LEDs seems much dimmer to the eye than, say, green and yellow wavelengths, per actual photon energy.If you look atefficiency(expressed in %; energy out per energy in), then phosphors will simply decrease it. But luminous efficiency is lm/W and weighed by human vision. This is also why deep blue / deep red LEDs and obviously infrared LEDs are not rated in lumens at all, the numbers would be small or in case of IR LEDs, zero.

author: DavidKo
author_rank: Frequent Contributor
timestamp: June 05, 2023, 08:08:56 am
content: Quote from: ELS122 on May 31, 2023, 11:42:45 pmWhat you mean by that? White LED always uses phosphor conversion. Most of high power yellow LEDs uses phosphor conversion too (I'm not sure with red). All this things are already on the market.Arc lamps are out of the market and had been replaced by halogen lamps, Xenon gas discharge lamps, Hg tubes etc. Arc lamp is pain due to the maintenance and issues they have (EMC will be real challenge, arc stability, ozone generation etc.).

author: Gyro
author_rank: Super Contributor
timestamp: June 05, 2023, 08:57:06 am
content: Quote from: DavidKo on June 05, 2023, 08:08:56 amThe last time I saw open (carbon) arc lamps was at a circus about 50 years ago.Xenon, Metal Halide, High pressure HG etc. (the ones the OP was actually referring to)arearc lamps, with the arc enclosed in a high temperature quartz tube within an outer glass envelope or other protection.As Jwillis pointed out, Phosphor coating has been widely used on the inside of the outer envelopes of High pressure Hg bulbs for many decades in order to improve their colour rendering...https://duckduckgo.com/?q=philips+mercury+bulb&atb=v328-1&iar=images&iax=images&ia=images. Metal Halide, Xenon, and UHP Hg don't need this because they already have very good colour spectrums.Low pressure Hg are of course standard florescent tubes, which have pretty much always (after the 1920s) used phosphor coatings.

author: tszaboo
author_rank: Super Contributor
timestamp: June 05, 2023, 11:13:28 am
content: Quote from: Jwillis on June 01, 2023, 12:44:42 pmIt doesn't mean it's a cheap production step to implement. Or that all the technical issues are resolved and that it's ready for mass production. Maybe the setup costs are high, or require expertise that is not available widely.

author: Gyro
author_rank: Super Contributor
timestamp: June 05, 2023, 02:14:28 pm
content: Quote from: ELS122 on June 05, 2023, 10:47:35 amNope, definitely a phosphor, it adds some red end into the spectrum.