The l phoneme (as in 'long' ɪɒŋ, 'hill' hɪl) is a lateral approximant. This is a consonant in which the passage of air through the mouth does not go in the usual way along the centre of the tongue; instead, there is complete closure between the centre of the tongue and the part of the roof of the mouth where contact is to be made (the alveolar ridge in the case of l). Because of this complete closure along the centre, the only way for the air to escape is along the sides of the tongue. The lateral approximant is therefore somewhat different from other approximants, in which there is usually much less contact between the articulators. If you make a long I sound you may be able to feel that the sides of your tongue are pulled in and down while the centre is raised, but it is not easy to become consciously aware of this; what is more revealing (if you can do it) is to produce a long sequence of alternations between d and I without any intervening vowel. If you produce dldldldldl without moving the middle of the tongue, you will be able to feel the movement of the sides of the tongue that is necessary for the production of a lateral. It is also possible to see this movement in a mirror if you open your lips wide as you produce it. Finally, it is also helpful to see if you can feel the movement of air past the sides of the tongue; this is not really possible in a voiced sound (the obstruction caused by the vibrating vocal folds reduces the airflow), but if you try to make a very loud whispered I, you should be able to feel the air rushing along the sides of your tongue.

We find I initially, medially and finally, and its distribution is therefore not particularly limited. In BBC pronunciation, the consonant has one unusual characteristic: the realization of I found before vowels sounds quite different from that found in other contexts. For example, the realization of I in the word 'lea' li: is quite different from that in 'eel' i:l.The sound in 'eel' is what we call a "dark I"; it has a quality rather similar to an [u] vowel, with the back of the tongue raised. The phonetic symbol for this sound is Ɨ. The sound in 'lea' is what is called a "clear I"; it resembles an [i] vowel, with the front of the tongue raised (we do not normally use a special phonetic symbol, different from I, to indicate this sound). The "dark I" is also found when it precedes a consonant, as in 'eels' i:lz. We can therefore predict which realization of I (clear or dark) will occur in a particular context: clear I will never occur before consonants or before a pause, but only before vowels; dark I never occurs before vowels. We can say, using terminology, that clear I and dark I are allophones of the phoneme I in complementary distribution. Most English speakers do not consciously know about the difference between clear and dark I, yet they are quick to detect the difference when they hear English speakers with different accents, or when they hear foreign learners who have not learned the correct pronunciation. You might be able to observe that most American and lowland Scottish speakers use a "dark I" in all positions, and don't have a "clear I" in their pronunciation, while most Welsh and Irish speakers have "clear I" in all positions.

Another allophone of I is found when it follows p, k at the beginning of a stressed syllable. The I is then devoiced (i.e. produced without the voicing found in most realizations of this phoneme) and pronounced as a fricative. The situation is similar to the aspiration found when a vowel follows p, t, k in a stressed syllable: the first part of the vowel is devoiced.