SCR halogen lamp flickers? - Page 1
Forum section: electronics / beginners

author: smile
author_rank: Regular Contributor
timestamp: March 05, 2022, 09:41:53 pm
content: Hello, I got SCR from chinahttps://www.aliexpress.com/item/4001118971797.html?spm=a2g0o.productlist.0.0.415b337fyREnaq&algo_pvid=32eebc90-53fb-4129-871f-9ff46701c9a5&algo_exp_id=32eebc90-53fb-4129-871f-9ff46701c9a5-32&pdp_ext_f=%7B%22sku_id%22%3A%2210000014541279555%22%7D&pdp_pi=-1%3B1.99%3B-1%3B66%40salePrice%3BEUR%3Bsearch-mainSearchhalogen lamp 50W flickers, is there easy way to solve this.The flicker is seen on mobile phone camera, and a specializes tester shows 37% flicker.

author: Zero999
author_rank: Super Contributor
timestamp: March 06, 2022, 12:47:48 pm
content: It's a phase controlled dimmer. The flicker is inevitable.

author: BrokenYugo
author_rank: Super Contributor
timestamp: March 06, 2022, 06:57:13 pm
content: That's how a solid state dimmer works, it clips out some of the sine wave to add periods of deadtime, reducing the RMS voltage, naturally this adds flicker, which is only smoothed by the heat capacity of the filament.Halogen seems more prone to flicker/shimmer if dimmed than a regular tungsten bulb, something to to do with the filament design I guess.

author: james_s
author_rank: Super Contributor
timestamp: March 07, 2022, 04:31:50 am
content: Many halogen bulbs incorporate a diode to drop the voltage, I believe this is done in order to get a more compact filament. The lamps with a diode tend to flicker anyway, I haven't tried one on a dimmer but it's possible it could cause additional effects.

author: Circlotron
author_rank: Super Contributor
timestamp: March 07, 2022, 05:59:30 am
content: Halogen lamps don't always like to be dimmed. They need to run not below a minimum temperature for the halogen cycle to work otherwise they can fail.https://en.wikipedia.org/wiki/Halogen_lamp#Effect_of_voltage_on_performance

author: Siwastaja
author_rank: Super Contributor
timestamp: March 07, 2022, 08:43:28 am
content: Incandescent bulbs do flicker even when not dimmed, simply because of the sinusoidal mains voltage, made even worse by the U^2/R power relationship.Thermal "inertia" of the filament smoothes the flicker, but not completely. Flicker is small enough so that practically everyone, even those sensitive to flicker, are fine in incandescent light. But if you shoot animation / stop motion / etc. (where you expect every frame to have the same exposure), or do scientific measurement expecting to get repeatable photographs, then this flicker with maybe 10-30% of amplitude in intensity, plus a color shift during the cycle, is a showstopper. The simplest solution is to use long enough exposure time. If unable to do that, rectifying the AC power and feeding the bulbs with DC is really the only option. High-frequency (maybe a kHz) PWM is acceptable. This allows you to build a feedback loop based on measured power, or even better, light intensity.

author: Terry Bites
author_rank: Super Contributor
timestamp: March 07, 2022, 11:57:08 am
content: If you dim this type of lamp bellow its normal operating temperature you will probably disrupt the "halogen cycle" and the bulb will die prematurely.Soon it will be hard to buy halogen bulbs a the world wide phase out continues.

author: Siwastaja
author_rank: Super Contributor
timestamp: March 07, 2022, 01:14:32 pm
content: The lifetime gain from the dimming itself outweighs the disrupting of the "halogen cycle" by a great margin, I think.Dimming increases the likelihood of glass discoloration by the tungsten particles, though. This is made worse by the fact that a typical halogen bulb has more (thicker) filament, and much much smaller glass envelope. Undimmed halogen bulbs are not always free of this effect, either, so the halogen cycle is not perfect. Dimming just makes it work worse.It would be interesting to know what OP is doing. Incandescent bulbs serve some niche areas quite well. Especially, if you need very high quality (high CRI) light for photography or scientific purposes, or just enjoy the light quality, a short-lived halogen bulb ("projector" type) which runs at 3400K color temperature looks literally quite "cool" compared to what we usually think incandescent bulbs look like, providing enough blue component to be usable, yet CRI of 100. The efficiency is surprisingly good, as well. The real downside is the 50-100 hour service life of these bulbs. Better stockpile a lot! (I have used normal 12V 2000-hour or 4000-hour halogen bulbs overvoltaged at 14-15V for the same purpose, because these are/were very cheaply available).

author: james_s
author_rank: Super Contributor
timestamp: March 07, 2022, 05:35:18 pm
content: Quote from: Siwastaja on March 07, 2022, 01:14:32 pmTo a point, yes. I'm not sure where the balance point is but I do know it was fairly common with those halogen torchier lamps that were popular around 20 years ago for people to leave them on dimmed way down and by morning the bulb would be all black. Often it would clear up after a while if you run it at full brightness but sometimes they would just burn out. It was common for halogen lamps used in copier and laser printer fuser rollers to turn black too.