Another "LED bulbs have mind of their own" post
April 10, 2022 8:48 AM   Subscribe

I have three 17.5 watt dimmable LEDs in a bathroom vanity light fixture on a dimmer switch. Flick them on, they work great. Flick them off, fine. Try to turn them back on again though, and they won't come on for a few minutes. They eventually always do, if you leave the switch on, but it can be a good 5 minutes. Can I fix this? Am I going to burn the house down?

Previous owner installed the fixture and dimmer, and there were LED bulbs in when I moved in, so I assume that is the fixture's intended use. I don't remember what wattage bulbs they had in - I wanted brighter bulbs. They liked "warm romantic lighting" and must never have had to fish a cat hair out of their eye or put on makeup! I don't use the dimmer, it's always at 100%.

As for wattage rating of the fixture, I can't tell without dismounting it, but I expect it is mid-grade Orange Box Store or Blue Box Store (based on their other choices). The dimmer is a Lutron. The only other thing plugged into the bathroom circuit is my toothbrush.

1953 house, modern wiring.

Anybody understand electricity enough to diagnose this? Google isn't helping. Don't really want to burn down the house!
posted by bluesky78987 to Home & Garden (7 answers total)
Best answer: Dimming LED bulbs reliably and well isn't really a solved problem yet. The bulbs and the dimmer switches both can be wonky.

I think you should start by taking each of the bulbs and placing them in a non-dimmable fixture, like a normal table lamp, and see if they work right there. I suspect they will work fine, and if so, you should replace the dimming light switch in your bathroom with a basic on/off switch since you don't use the dimmer anyway.

I say I suspect the bulbs are fine because you are describing them all failing to work right simultaneously; if the bulbs were wonky they wouldn't always all three do the same wonky thing.
posted by fritley at 9:31 AM on April 10, 2022

Best answer: Some dimmers have an adjustable "minimum" level, and this minimum level may be too low for some LED bulbs to turn on. If you are turning it on at the minimum level, when it fails to re-light, then it sounds like your dimmer's minimum is borderline, so that it sometimes works, sometimes doesn't... You can pull off the wallplate and see if there are minimum (and/or maximum) dimmer adjustments. Dimmer adjustment example from Lutron
posted by soylent00FF00 at 11:18 AM on April 10, 2022 [1 favorite]

Best answer: Soylent hex color is on the right track I think. Lutron makes quality led dimmers, but not every dimmer they make is meant for LED use.

Also, the bulbs are 17.5w led, or 17.5w *equivalent*? 17.5w per bulb is a lot of led, and the three together should be meeting an led dimmer minimum no problem (many will say min 10 watts. Newer ones are often less). If they are equivalent, they might be 3w each or less and not pulling enough power to let the dimmer work correctly.

Since they usually come on once and then don't like to come back on, it could be that during the initial on, the capacitors in the direct ac drivers are pulling enough power to make it work, while subsequent flips they are still retaining some power so the inrush current isn't so high and they don't turn on. I would guess the 5 min before they turn on is the capacitors dropping to a point where the dimmer switch recognizes enough current pull and goes on.

So yeah, try them elsewhere, and replace the dimmer if they work fine somewhere else.
posted by jellywerker at 11:31 AM on April 10, 2022 [1 favorite]

Best answer: A lot of LEDs, even dimmable models, seem to need a certain minimum voltage before they'll come on. Is your dimmer a push on/push off type with a knob, or a switch lever where the position of the switch is the dimmer? I had a dimmer in our bathroom that was the switch lever type, and from "off" there was the dimmer range, and then at the top there was a very soft click into "full on". If I absently flicked the switch up, but not past that soft click into "fully on", the LEDs would not turn on. If I ramped it to "full on", the bulbs would light, and then I could dim it down a little before they cut out.

Downstairs, I have LEDs on a knob type, push on/push off dimmer switch. As long as the knob is cranked all the way up, without fail, the lights will come on every single time. But if the knob had been dimmed down some, they usually won't come on until it's cranked all the way up. Similar behavior from two different types of dimmer switches. Perhaps something similar is happening with your lights?

You should be totally fine with the wattage rating. It can be a little confusing with LEDs, as they will often advertise "60W equivalent" or so, but are only using 10W or whatever. So, you're definitely not in danger of exceeding the fixture's power rating, but you do still need to be aware of heat. The standard Edison screw-in type LEDs that replace incandescent bulbs can generate a lot of heat, and so even though you may only have a 10W bulb in a fixture rated for 60W, the bulb may still run into heat failure issues, especially in an enclosed fixture. Some of these screw-in LEDs are rated for use in enclosed fixtures, some are not.
posted by xedrik at 11:33 AM on April 10, 2022

Best answer: If you never use the dimmer just replace it with a regular on/off switch.

17.5W LED is a pretty big draw; that's like a 200W incandescent equivalent. 7.5W would be closer to 60W though. Either way any Edison base bulb fixture is going to handle 25W per socket minimum so you shouldn't worry about overloading the fixture. Non enclosed rated bulbs generally will still work they will just have reduced driver lifespans.
posted by Mitheral at 12:06 PM on April 10, 2022 [2 favorites]

Best answer: Previous owner installed the fixture and dimmer, and there were LED bulbs in when I moved in, so I assume that is the fixture's intended use.

There's your problem right there. Totally not a safe assumption. As others have said LED+dimmer combo is really not a solved problem yet. Lots of people want the flexibility of a dimmer and the long life and lower power draw of an LED and don't do the research and/or expect that in a few years we'll have figured dimmable LED lamps out better.
posted by potrzebie at 1:07 PM on April 10, 2022 [1 favorite]

Response by poster: Thanks everybody. I'm going to get the switch replaced with an "on/off" style. (For those curious, the bulbs are 100 watt equivalent, 17.5W actual, and the dimmer is a regular on/off switch with a little slider along the side, which stays at fully "on". Appreciate the advice and now I won't worry about burning the house down until I can get the dimmer replaced.
posted by bluesky78987 at 8:41 AM on April 12, 2022

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