In short: Dia Light is L'Oreal Professionnel's ammonia-free, acidic demi-permanent gloss. Mix it 1:1.5 with DIActivateur developer (6, 9 or 15 vol), apply to dry hair and process for up to 20 minutes. It adds tone and high shine with zero lift — ideal for toning blondes, refreshing colour and blending the first greys.
Written for salon professionals. Reviewed against current L'Oreal Professionnel guidance.
What is Dia Light?
Dia Light is L'Oreal Professionnel's ammonia-free, acidic demi-permanent colour — a gel-crème that deposits tone and a glass-like shine without lifting the natural base. Built on Gentle Acid Technology, its pH sits close to the hair's own, so it works with the cuticle rather than forcing it open. The result is a translucent, luminous finish that's especially kind to colour-treated or sensitised hair.
Because it deposits only — zero lift — Dia Light is a toning and glossing colour, not a lightener or a heavy grey-coverage product. That's exactly why colourists reach for it:
- Toning and personalising blondes after a lightening service
- Refreshing faded mid-lengths and ends
- Adding shine and a gloss top-up between permanent colours
- Softly blending the first greys
- Neutralising or enhancing tone on previously coloured hair
How does Dia Light's acid technology work?
Conventional permanent colour is alkaline and swells the hair to deposit and lift pigment. Dia Light is the opposite: its acidic pH and cationic polymers smooth and seal the cuticle as colour is deposited. No ammonia, no lift — just tone and a high-gloss, vinyl-like finish. In practice that means a gentle service that maintains hair integrity, making it a safe choice on porous, pre-lightened or repeatedly coloured hair.
What's the Dia Light mixing ratio?
Dia Light mixes at a 1:1.5 ratio with its dedicated DIActivateur developer — one tube (50ml) of colour to 75ml of DIActivateur. Mix to a smooth, homogeneous cream in a bowl, bottle or shaker, and apply to dry, unwashed hair.
Which DIActivateur developer should you use?
Dia Light uses low-volume DIActivateur developers, chosen by what you're toning:
| Developer | Strength | Best for |
|---|---|---|
| DIActivateur 6 vol | 1.8% | Blondes, tone-on-tone deposit, soft results |
| DIActivateur 9 vol | 2.7% | Brunettes and standard depositing |
| DIActivateur 15 vol | 4.5% | Reds and fashion shades for maximum vibrancy |
Whatever the volume, the mix stays 1:1.5 and there's no lift — the developer simply drives even deposit.
How do you apply Dia Light?
- Apply the mix to dry, unwashed hair.
- Process for up to 20 minutes at room temperature (toning blondes can be much faster — see Milkshakes below).
- Emulsify: add a little warm water and massage gently before rinsing.
- Rinse thoroughly and finish with a colour-safe shampoo.
Always carry out an allergy alert/sensitivity test 48 hours before each service.
What are Dia Light Milkshakes?
The Milkshake shades are Dia Light's cool, very pale toners at levels 9 and 10 — made for toning and glossing pre-lightened blondes. They work fast, often in just 2–10 minutes, to knock back unwanted warmth and leave a soft, expensive-looking finish. They're the go-to for that post-balayage toner and for refreshing a blonde between appointments.
Does Dia Light cover grey?
Dia Light blends and tones grey rather than fully covering it. It can soften and gloss the first greys (roughly up to 30%), but it won't give opaque white coverage. For fuller grey coverage, step up to Dia Richesse / Dia Color (ammonia-free demi, up to 70% grey) or a permanent system such as INOA or Majirel for up to 100%.
Dia Light vs Majirel vs INOA: what's the difference?
| Dia Light | Majirel | INOA | |
|---|---|---|---|
| Type | Acidic demi-permanent | Permanent | Permanent (ammonia-free) |
| Ammonia | No | Yes | No |
| Lift | None | Up to 3 levels | Up to 3 levels |
| Grey coverage | Tones/blends (up to ~30%) | Up to 100% | Up to 100% |
| Best for | Toning, glossing, refreshing | Fashion colour, full coverage | Sensitive scalps, full coverage |
Quick reference
- Type: ammonia-free acidic demi-permanent gloss
- Lift: none (deposit only)
- Mixing ratio: 1:1.5 (50ml colour : 75ml DIActivateur)
- Developers: DIActivateur 6 / 9 / 15 vol
- Processing: up to 20 minutes (Milkshakes 2–10 min)
- Grey: tones/blends; for coverage use Dia Richesse/Color or a permanent
Frequently asked questions
Is Dia Light permanent?
No — it's a demi-permanent colour that deposits tone and fades gradually, with no harsh regrowth line.
Does Dia Light lift?
No. Dia Light has zero lift; it only deposits tone and shine. To lighten, pre-lighten first or use a permanent lifting colour.
What is the Dia Light mixing ratio?
1:1.5 — one 50ml tube of colour to 75ml of DIActivateur developer.
Which developer do you use with Dia Light?
DIActivateur 6 vol for blondes, 9 vol for brunettes, and 15 vol for reds and fashion shades.
How long does Dia Light take to process?
Up to 20 minutes; the cool Milkshake toners on blondes can be as quick as 2–10 minutes.
Does Dia Light cover grey?
It tones and blends the first greys (around up to 30%) but doesn't give full coverage. For that, use Dia Richesse/Dia Color or a permanent colour like INOA or Majirel.
What are Dia Light Milkshakes?
Cool level 9 and 10 toning shades designed to gloss and neutralise pre-lightened blondes quickly.
Is Dia Light ammonia-free?
Yes — it's an acidic, ammonia-free formula, gentle enough for colour-treated and sensitised hair.
Stocking up
Dia Light is one of the most versatile colours on the trolley — a fast, gentle gloss-and-tone that keeps blonde clients coming back and adds shine to every refresh. Browse the full Dia Light range, the Milkshake toners and DIActivateur developers in our colour section, with trade pricing and fast delivery as standard.
Professional use only. Always follow the manufacturer's instructions and complete the recommended allergy alert test before every application.
Written by Charlotte Read, Content Writer at Hairco & Beauty. Charlotte has over six years' experience in professional hair and beauty, and our guides are informed by colleagues with 100+ years of combined salon experience and by insight from the trade customers we supply. More about our content.
