LED strips — the specifications that decide whether you are happy
Almost every listing leads with the wrong number. Here is what to read instead, and why cheap strips look cheap.
LED strip listings compete on two numbers: length and how many colours the app can produce. Neither predicts whether the light in your room will look good.
The specifications that do are usually further down the page, and some are not listed at all — which is itself informative.
LED density
The number of diodes per metre. Listed as 30, 60, 120, or 144 LEDs/m.
This is the single most visible difference between a strip that looks like lighting and one that looks like a row of dots. At 30/m the individual diodes are distinct — behind a diffuser it reads as a dotted line, and pointed at a wall it produces scalloped bands of light rather than an even wash.
At 60/m the dots merge at normal viewing distances behind any diffuser. At 120/m and above they merge with no diffuser at all.
Under a kitchen cabinet where you see the light but not the strip, 60/m is enough. Anywhere the strip itself is visible, or where it curves, 120/m is the difference between “installed lighting” and “stuck a strip on”.
Colour temperature, and the CRI question
Listings for white strips specify a temperature: 2700K is warm domestic, 4000K is neutral, 6000K+ is the blue-white of an office or a car park.
The number that is almost never listed is CRI — colour rendering index, how accurately the light shows colour. Cheap phosphors produce light that measures as white but renders skin, wood, and food badly; a CRI of 70 makes a kitchen look grey and unappetising, which is a large part of why cheap LED lighting feels cheap.
Anything above CRI 90 is good. The relevant fact is that listings which do not mention CRI are almost never above 80 — a seller with a high-CRI strip puts the number in the title, because it costs more to make.
For anything lighting a work surface or a room people sit in, treat a missing CRI figure as a specification failure rather than an omission.
Power, and the thing that goes wrong at length
A strip draws a fixed wattage per metre — typically 5 to 15 W/m depending on density and brightness. Two consequences people discover after installing:
The supply must exceed the total draw with headroom. A 5-metre run at 12 W/m needs 60 W, and a supply rated at exactly 60 W will run hot and fail early. Around 20% headroom is the working rule.
Voltage drop over distance. Power is injected at one end and the far end of a long run sits at a lower voltage — visibly dimmer, and on white strips noticeably warmer in colour. On 12 V strips this becomes obvious past about 5 metres. Either inject power at both ends, or use a 24 V strip, where the same drop is proportionally smaller.
A listing selling a 10-metre 12 V roll with a single small supply is selling something that will not look the way the photographs do.
The IP rating
IP20 is bare. IP65 is silicone-coated and splash-resistant. IP67 is sealed in a sleeve.
Two things worth knowing. The coating changes the light — a silicone sleeve diffuses slightly, which is often flattering, and yellows over years of UV. And sealed strips cannot be cut and rejoined easily, so you are committing to the run length you order.
For indoor use IP20 is correct and cheaper. Kitchens and bathrooms want IP65. Outdoors wants IP67 and a supply rated for it.
What the app does not fix
RGB strips mix red, green, and blue to produce white, and the result is a poor white — it has spikes in the spectrum where the three diodes sit and gaps between them, so it renders colour badly no matter what the app says.
RGBW and RGBWW strips add a dedicated white diode. If you intend to use the strip as light rather than as colour, this distinction matters more than the number of effects in the app.
Reading a listing quickly
In order:
- LEDs per metre. 60 minimum, 120 if the strip is visible.
- CRI. If it is not stated, assume it is low.
- Voltage. 24 V for runs over about 5 m.
- Supply wattage against strip wattage × length, with headroom.
- RGBW rather than RGB, if you want usable white.
- IP rating matched to where it goes.
Length and effect count — the two things the title leads with — come last.
The short version
Cheap strips are cheap in ways the headline specification hides: too few diodes, low CRI, an undersized supply, and RGB pretending to be white. All four are visible in the listing if you know which lines to read, and all four are the difference between lighting a room and sticking a light in it.